Harr: Urinalysis and Body Fluids
Which of the following crystals is the cause of gout? A. Uric acid or monosodium urate B. Calcium pyrophosphate or apatite C. Calcium oxalate D. Cholesterol
A Although all of the crystals mentioned can cause crystal-induced arthritis, uric acid and sodium urate crystals cause gout and are seen in about 90% of gout patients.
When collecting CSF, a difference between opening and closing fluid pressure greater than 100 mm H2O indicates: A. Low CSF volume B. Subarachnoid hemorrhage C. Meningitis D. Hydrocephalus
A Normal CSF volume in adults is 100-160 mL. When volume is low, an abnormally high difference is observed between the opening and closing pressure. The difference is normally 10-30 mm H20, after removal of 15-20 mL. Low opening pressure is caused by reduced volume or block above the puncture site. High opening pressure may result from high CSF volume, CNS hemorrhage, or malignancy.
Which test best correlates with the severity of HDN? A. Rh antibody titer of the mother B. Lecithin/sphingomyelin (L/S) ratio C. Amniotic fluid bilirubin D. Urinary estradiol
C Amniotic fluid bilirubin is the best index of the severity of HDN and is measured by scanning or diode array spectrophotometry across the 550-365 nm range. When hemoglobin produces a positive slope at 410 nm, the bilirubin should be extracted with chloroform prior to scanning. Extraction methods give the best correlation with RBC destruction.
Which of the following is an inappropriate procedure for performing routine CSF analysis? A. A differential is done only if the total WBC count is greater than 10/μL B. A differential should be done on a stained CSF concentrate C. A minimum of 30 WBCs should be differentiated D. A Wright's-stained slide should be examined rather than a chamber differential
A A relative (percent) increase in PMNs may be significant even when the WBC count does not exceed the upper limit of normal. For this reason, a WBC differential using a concentrated CSF sample is always performed on neonates and when the WBC count is > 5/μL. Cytocentrifugation should be used to concentrate the cells followed by staining with Wright's stain.
Which of the following statements about amniotic fluid bilirubin measured by scanning spectrophotometry is true? A. The 410-nm peak is due to hemoglobin and the 450-nm peak is due to bilirubin B. Baseline correction is not required if a scanning spectrophotometer is used C. Chloroform extraction is necessary only when meconium is present D. In normal amniotic fluid, bilirubin increases with gestational age
A Amniotic fluid bilirubin reflects the extent of fetal RBC destruction in cases of hemolytic disease of the newborn (HDN). It is measured by scanning the fluid from 350 to 600 nm, then drawing a baseline using the points at 365 nm and 550 nm. The delta absorbance (ΔA) of hemoglobin at 410 nm and bilirubin at 450 nm are determined by subtracting the absorbance of the baseline from the respective peaks. Samples that are not grossly hemolyzed can be corrected for oxyhemoglobin by subtracting 5% of the ΔA at 410 nm from the ΔA at 450 nm. When hemolysis is severe or meconium is present, the bilirubin must be extracted in chloroform before measuring absorbance. Bilirubin normally decreases with increasing gestational age because fetal urine contributes more to amniotic fluid volume as the fetus matures. The bilirubin concentration must be correlated with gestational age in order to correctly evaluate the severity of HDN.
Which assay result is often approximately 25% below the expected level in pregnancies associated with Down syndrome? A. Serum unconjugated estriol B. L/S ratio C. Amniotic fluid bilirubin D. Urinary chorionic gonadotropin
A Estriol is produced by the placenta as well as the fetal and maternal adrenal glands and liver. Free estriol produced by the placenta is rapidly conjugated by the maternal liver. Maternal serum unconjugated (free) estriol is almost all derived from the fetus and is a direct reflection of current fetal placental function. Serum unconjugated estriol (uE3) measured during the second trimester is used along with serum AFP, hCG, and dimeric inhibin A as part of the quad marker screening test for Down syndrome. AFP and uE3 are decreased by approximately 25%, inhibin A is increased by a factor of approximately 1.8, and hCG is increased by a factor of approximately 2.5 in Down syndrome pregnancies. When all four assays are combined with adjustments for maternal age, gestational age, race, maternal weight, and diabetes, the detection rate is approximately 70-80% and the false-positive rate 7%.
Which statement regarding CSF is true? A. Normal values for mononuclear cells are higher for infants than adults B. Absolute neutrophilia is not significant if the total WBC count is less than 25/μL C. The first aliquot of CSF should be sent to the microbiology laboratory D. Neutrophils compose the majority of WBCs in normal CSF
A Lymphocytes account for 40%-80% of WBCs in adults; monocytes and macrophages for 20%-50%. Neutrophils should be less than 10% of the WBCs. The reference range for WBCs in adults is 0-5/μL. Disease may be present when the WBC count is normal, if the majority of WBCs are PMNs. In infants, monocytes account for 50%-90% of WBCs, and the upper limit for WBCs is 30/μL. The first aliquot is sent to the chemistry department because it may be contaminated with blood or skin flora.
Which of the following statements about AFP is correct? A. Maternal serum may be used to screen for open neural tube defects B. Levels above 4 ng/mL are considered positive C. Elevated levels in amniotic fluid are specific for spina bifida D. AFP levels increase in pregnancies associated with Down syndrome
A Maternal serum AFP increases steadily until 2 months prior to full term as AFP passes from the fetal urine into the amniotic fluid. Because serum levels are dependent upon gestational age, upper reference limits depend upon last menstrual period dating. AFP is measured between 14 and 18 weeks gestation, and levels are reported as multiples of the median in order to permit interlaboratory comparison. When serum levels are high, ultrasound is used to determine fetal age and rule out twins. Increased maternal serum AFP levels (>2.5 MoM) may result from many diseases in addition to open neural tube defects such as spina bifida. These include anencephaly, ventral wall defects, congenital hypothyroidism, and Turner's syndrome. Decreased levels (<0.75 MoM) may be seen in approximately 25% of Down syndrome pregnancies.
Which of the following laboratory results on a serous fluid is most likely to be caused by a traumatic tap? A. An RBC count of 8,000/μL B. A WBC count of 6,000/μL C. A hematocrit of 35% D. A neutrophil count of 55%
A Normal fluids have a WBC count less than 1,000/μL, but counts between 1,000 and 2,500/μL may be seen in both exudates or transudates. All WBC types are present, but no type should account for more than 50% of the leukocyte count. An RBC count below 10,000/μL is usually caused by a traumatic tap. A fluid hematocrit similar to blood is caused by a hemothorax. Pleural fluids containing > 100,000/μL RBCs are associated most often with malignancies, but are also seen in trauma and pulmonary infarction.
Which of the following hematology values best frames the upper reference limits for peritoneal fluid? WBC Count % of PMNs RBC Count A. 300/μL 25% 100,000/μL B. 10,000/μL 50% 500,000/μL C. 50,000/μL 50% 500,000/μL D. 100,000/μL 75% 1,000,000/μL
A Peritoneal fluid normally has a WBC count of less than 300/μL. Neutrophils should account for no more than 25% of the WBCs. A majority of PMNs indicates bacterial infection of the peritoneum. Lymphocytosis suggests malignancy, tuberculosis, cirrhosis, and lymphatic leakage. Peritoneal fluid amylase is elevated in most cases of acute pancreatitis. Peritonitis is suspected when the fluid LD is greater than 40% of the serum level. In contrast, normal pleural fluid has a WBC count usually below 1,000/μL. Exudative fluids usually have a WBC count above 10,000/μL, but values tend to overlap noninflammatory fluids. The PMNs should comprise 50% of the WBCs or less, and the RBC count should be less than 100,000/μL.
Which of the following statements regarding the L/S ratio is true? A. A ratio of 2:1 or greater usually indicates adequate pulmonary surfactant to prevent respiratory distress syndrome (RDS) B. A ratio of 1.5:1 indicates fetal lung maturity in pregnancies associated with diabetes mellitus C. Sphingomyelin levels increase during the third trimester, causing the L/S ratio to fall slightly during the last 2 weeks of gestation D. A phosphatidylglycerol (PG) spot indicates the presence of meconium in the amniotic fluid
A Pulmonary surfactants are mainly disaturated lecithins produced by type II granular pneumocytes. The L/S ratio increases toward the end of the third trimester due to increased production of lecithin. The concentration of sphingomyelin remains constant throughout gestation and serves as an internal reference. Meconium contains less lecithin than amniotic fluid and will usually decrease the L/S ratio; however, meconium produces a spot that can be misinterpreted as lecithin, leading to a falsely increased L/S ratio. Sufficient PG to produce a spot is seen only when the L/S ratio is 2:1 or higher. PG is not present in either blood or meconium and, therefore, its presence indicates fetal lung maturity. In diabetes, the fetal lungs may mature more slowly than normal, and infants may develop RDS when the L/S ratio is 2:1 or slightly higher. For this reason, an L/S of 3:1 more closely correlates with fetal lung maturity when testing amniotic fluid from diabetic mothers. As in all other cases, when the amniotic fluid from a diabetic mother is positive for PG, fetal lung maturity is established.
Which statement about synovial fluid in RA is true? A. Synovial/serum IgG is usually 1:2 or higher B. Total hemolytic complement is elevated C. Ninety percent of RA cases test positive for rheumatoid factor in synovial fluid D. Demonstration of rheumatoid factor in joint fluid is diagnostic for RA
A Rheumatoid factor can be present in both serum and synovial fluids from patients with RA, SLE, and other inflammatory diseases. Rheumatoid factor is present in synovial fluid of approximately 60% of patients with RA. Normally, IgG in synovial fluid is about 10% of the serum IgG level. CH50 levels in serum and synovium are more differential. Both are increased in Reiter's syndrome but are often low in SLE; synovial CH50 is decreased and serum CH50 is normal (or increased) in RA.
In which type of arthritis is the synovial WBC count likely to be greater than 50,000/μL? A. Septic arthritis B. Osteoarthritis C. RA D. Hemorrhagic arthritis
A The WBC count is elevated in all types of arthritis, but is greatest (50,000-100,000/μL) in septic arthritis. Neutrophils comprise less than 25% of WBCs in normal and noninflammatory arthritis, but are above 50% in inflammatory and septic arthritis. Fluids are diluted in saline because acetic acid causes a mucin clot to form. WBC counts should be performed within 1 hour of collection because the WBC count will diminish over time.
Which of the following hematology values best frames the upper reference limits for synovial fluid? WBC Count %of PMNs RBC Count A. 200/μL 25% 2,000/μL B. 5,000/μL 50% 10,000/μL C. 10,000/μL 50% 50,000/μL D. 20,000/μL 5% 500,000/μL
A The WBC count of normal joint fluid is 200/μL or less. Values above 5,000/μL cause the fluid to be purulent and occur in septic arthritis, RA, and gout. WBC counts greater than 50,000 μL indicate septic arthritis. The majority of WBCs in normal fluid are monocytes, which usually account for 50%-65%. Neutrophils and lymphocytes should account for no more than 25% each. An increase in RBCs occurs in cases of infectious and hemorrhagic arthritis or results from a traumatic tap. Hemorrhagic fluid will appear turbid, red to brown, and often clotted. Inflammatory arthritis can allow fibrinogen to enter the fluid and thus clot. Fluid from a hemophiliac will not clot in spite of its bloody appearance.
In what suspected condition should a wet prep using a warm slide be examined? A. Cryptococcal meningitis B. Amoebic meningoencephalitis C. Mycobacterium tuberculosis infection D. Neurosyphilis
B Amoeba in CSF appear very similar to monocytes in stained films but can be differentiated by their characteristic pseudopod mobility in a wet prep on a prewarmed slide. Naegleria fowleri and Acanthamoeba spp. are causative agents of primary amoebic meningoencephalitis.
Which crystal causes "pseudogout"? A. Oxalic acid B. Calcium pyrophosphate C. Calcium oxalate D. Cholesterol
B Calcium pyrophosphate crystals occur as needles or small rhombic plates and can be confused with uric acid. They rotate plane polarized light but not as strongly as uric acid. Synovial fluid should never be collected in tubes containing powdered ethylenediaminetetraacetic acid (EDTA) because it may form crystals that can be mistaken for in vivo crystals. The recommended anticoagulant is sodium heparin, although liquid EDTA may be used.
Given the following data, determine the corrected CSF WBC count. CSF Values Peripheral Blood Values RBCs 6,000/μL 4.0 × 106/μL WBCs 150/μL 5.0 × 103/μL A. 8 WBC/μL B. 142 WBC/μL C. 120 WBC/μL D. 145 WBC/μL
B Corrected WBC count = WBCs in CSF - [(Blood WBCs × CSF RBCs) ÷ Blood RBCs] Corrected WBC count = 150/μL - [(5,000/μL WBCs × 6,000/μL RBCs) ÷ 4,000,000/μL RBCs] Corrected WBC count = 150/μL - 7.5/μL Corrected WBC count = 142/μL
Most cases of Down syndrome are the result of: A. Nondisjunction of an E chromosome (E trisomy) B. Nondisjunction of chromosome 21 (G trisomy) C. A 14-21 chromosome translocation D. Deletion of the long arm of chromosome 21
B Down syndrome can result from a 14-21 translocation or isochromosome formation, but most cases arise from nondisjunction of chromosome 21 during meiosis. A quad marker screen consisting of maternal serum AFP, hCG, dimeric inhibin A, and unconjugated estriol is used to screen for Down syndrome during the second trimester. If the test is positive, amniocentesis is performed, and 21 trisomy is investigated by chromosome karyotyping or FISH.
Which organism is the most frequent cause of bacterial meningitis in neonates? A. Neisseria meningitidis B. Group B Streptococcus C. Streptococcus pneumoniae D. Klebsiella pneumoniae
B Group B Streptococcus and E. coli are the two most common isolates in neonates. Haemophilus influenzae, S. pneumoniae, and N. meningitidis are the most common isolates in children. S. pneumoniae is the most frequent isolate in the elderly.
Which of the following results is consistent with fungal meningitis? A. Normal CSF glucose B. Pleocytosis of mixed cellularity C. Normal CSF protein D. High CSF lactate
B In fungal meningitis, the glucose will be low and the total protein elevated; however, unlike bacterial meningitis, the lactate is usually below 35 mg/dL. Fungal meningitis usually produces a pleocytosis of mixed cellularity consisting of lymphocytes, PMNs, monocytes, and eosinophils. In some cases, lymphocytes predominate; while in others, PMNs comprise the majority of WBCs.
Which of the following statements accurately describes hCG levels in pregnancy? A. Levels of hCG rise throughout pregnancy B. In ectopic pregnancy, serum hCG doubling time is below expected levels C. Molar pregnancies are associated with lower levels than expected for the time of gestation D. hCG returns to nonpregnant levels within 2 days following delivery, stillbirth, or abortion
B In normal pregnancy, hCG levels rise exponentially following implantation and peak at weeks 9-12, reaching in excess of 100,000 mIU/mL. Levels fall after the first trimester to about 20,000 mIU/mL and then remain at about that level through term. The hCG doubling time averages 2.2 days. In ectopic pregnancy, the expected increase between consecutive days is below normal. Hydatiform moles are associated with greatly elevated levels of hCG. Serum hCG can take up to 4 weeks to return to nonpregnant (<25 mIU/mL) or baseline (<5 mIU/mL) levels following delivery, stillbirth, or abortion.
What type of cell is a "ragocyte"? A. Cartilage cell seen in inflammatory arthritis B. A PMN with inclusions formed by immune complexes C. A plasma cell seen in RA D. A macrophage containing large inclusions
B Ragocytes are PMNs containing dark granules composed of immunoglobulins, but they may be seen in gout and septic arthritis as well as RA. LE cells may be seen in fluid from patients with SLE. Reiter's cells, macrophages with ingested globular inclusions, are seen in Reiter's syndrome and other inflammatory diseases.
Which is the reference method for determining fetal lung maturity? A. Human placental lactogen B. L/S ratio C. Amniotic fluid bilirubin D. Urinary estriol
B Respiratory distress syndrome develops when surfactants are insufficient to prevent collapse of the infant's alveoli during expiration. Tests measuring pulmonary phospholipid surfactants are the most specific and sensitive indicators of respiratory distress syndrome. An L/S ratio greater than 2:1 (in some laboratories 2.5:1) is the most widely accepted measure of fetal lung maturity. Most of the surfactants in the amniotic fluid are present in the form of lamellar bodies. These can be counted using an electronic cell counter at the settings for enumerating platelets.
Which of the following organisms accounts for the majority of septic arthritis cases in young and middle-age adults? A. H. influenzae B. Neisseria gonorrhoeae C. Staphylococcus aureus D. Borrelia burgdorferi
B Synovial fluid is normally sterile, and all of the organisms listed may cause septic arthritis. N. gonorrhoeae is responsible for about 75% of septic arthritis cases occurring in young and middle-aged adults. Staphylococcus spp. is responsible for the majority of cases involving the elderly, and is the most frequently found isolate from infected joint replacements. Haemophilus spp., Staphylococcus spp., and Streptococcus spp. are the most common causes of arthritis in young children.
Which of the following statements regarding serous fluids is true? A. The normal volume of pleural fluid is 30-50 mL B. Mesothelial cells, PMNs, lymphocytes, and macrophages may be present in normal fluids C. X-ray can detect a 10% increase in the volume of a serous fluid D. Normal serous fluids are colorless
B The serous fluids include pleural, pericardial, and peritoneal fluid. They form from ultrafiltration of plasma through serous membranes. These are lined with specialized epithelium called mesothelium. They comprise about 5% of the cells in serous fluid and may be difficult to differentiate from malignant cells. Pleural fluid volume is normally less than 10 mL. The volume of pericardial fluid is normally 10-50 mL and peritoneal fluid 30-50 mL. X-rays can detect an increase in serous fluids of 300 mL or more. Normal serous fluids are clear and range in color from straw to light yellow.
Which of the following conditions is commonly associated with an exudative effusion? A. Congestive heart failure B. Malignancy C. Nephrotic syndrome D. Cirrhosis
B Transudative fluids are caused by circulatory problems, usually decreased oncotic pressure or increased hydrostatic pressure. In contrast, exudative effusions are caused by inflammatory processes and cellular infiltration as seen in malignancy. In addition to a RBC count > 100,000/μL, malignancies often involve the lung, colon, breast, or pancreas and often produce carcinoembryonic antigen.
Which statement about CSF protein is true? A. An abnormal serum protein electrophoretic pattern does not affect the CSF pattern B. The upper reference limit for CSF total protein in newborns is one-half adult levels C. CSF IgG is increased in panencephalitis, malignancy, and neurosyphilis D. Antibodies to Treponema pallidum disappear after successful antibiotic therapy
C Although the blood-brain barrier excludes most plasma proteins, abnormal serum proteins can cause parallel CSF electrophoretic patterns. Therefore, an abnormal CSF pattern indicates CNS disease only if not duplicated by the serum pattern. Normal CSF total protein in newborns may be up to two times higher than adult levels. Antibodies to T. pallidum remain in CSF after treatment, but nontreponemal antibodies disappear. While the FTA-ABS test for specific antibodies is more sensitive, the VDRL test is often performed concurrently. A positive result for both tests is diagnostic of active tertiary syphilis.
SITUATION: A pregnant female was seen by her physician who suspected a molar pregnancy. An hCG test was ordered and found to be low. The sample was diluted 10-fold and the assay was repeated. The result was found to be grossly elevated. What best explains this situation? A. The wrong specimen was diluted B. A pipeting error was made in the first analysis C. Antigen excess caused a falsely low result in the undiluted sample D. An inhibitor of the antigen-antibody reaction was present in the sample
C Assays of intact hCG are double antibody sandwich immunoassays. One antibody reacts with the α subunit and the other with the β subunit. In assays where both antibodies are added together, a process called the "hook effect" is known to occur. In extreme antigen excess, the hCG saturates both antibodies, preventing sandwich formation. This results in a falsely low measurement of hCG.
The term effusion refers to: A. A chest fluid that is purulent B. A serous fluid that is chylous C. An increased volume of serous fluid D. An inflammatory process affecting the appearance of a serous fluid
C Effusions are classified as either transudates, exudates, or chylous. Transudates result from abnormal hemodynamics (e.g., congestive heart failure, liver disease), and exudates and chylous fluids from local disease. A pleural fluid that is purulent is called an empyemic fluid. Such a fluid has a WBC count of 10,000/μL or greater.
Which of the following CSF test results is most commonly increased in patients with multiple sclerosis? A. Glutamine B. Lactate C. IgG index D. Ammonia
C IgG Index = (CSF IgG ÷ serum IgG) (CSF albumin ÷ serum albumin) An IgG-albumin index is the ratio of CSF IgG:serum IgG divided by the CSF albumin:serum albumin. Values greater than 0.85 indicate CSF IgG production, as seen in multiple sclerosis; or increased CSF production combined with increased permeability, as seen in CNS infections. Multiple sclerosis is characterized by the presence of oligoclonal banding in the CSF in more than 90% of patients with active disease. The total protein and myelin basic protein are often increased and the glucose is decreased. Reye's syndrome results in hepatic failure, causing high CSF levels of ammonia and glutamine. CSF lactate is usually normal in patients with multiple sclerosis.
Following a head injury, which protein will identify the presence of CSF leakage through the nose? A. Transthyretin B. Myelin basic protein C. Tau protein D. C-reactive protein
C In cases of trauma, it may be necessary to differentiate rhinorrhea from CSF leakage, and this can be done by immunofixation electrophoresis to identify tau protein found in CSF but not serum. Tau protein is an enzymatically modified form of transferrin that migrates in the slow beta zone just behind unmodified transferrin. Transthyretin or prealbumin is present in far greater concentration in CSF than blood but may not be seen if CSF is diluted with nasal fluid. Myelin basic protein is a component of nerve sheaths and is present in CSF in about 60% of persons with MS. It is also found in persons with other demyelinating diseases, SLE, stroke and brain injury. C-reactive protein is elevated in the CSF of approximately two-thirds of persons with bacterial meningitis.
Which cell is present in the CSF in greater numbers in newborns than in older children or adults? A. Eosinophils B. Lymphocytes C. Monocytes D. Neutrophils
C In newborns, the upper reference limit (URL) for WBCs is 30/μL (URL for adults is 5/μL) with the majority of WBCs being monocytes or macrophages. In normal neonates, monocytes (including macrophages and histiocytes) account for about 75% of the WBCs, lymphocytes for about 20%, and PMNs for about 3%. In normal adults, lymphocytes account for about 60% of the WBCs, monocytes for about 35%, and PMNs for about 2%.
Which of the adult CSF values in the following table are consistent with bacterial meningitis? WBCs Lymph Mono Eos Neu Neuroectodermal Cells A. 50/μL 44% 55% 0% 0% 1% B. 300/μL 75% 21% 3% 0% 1% C. 2,000/μL 5% 15% 0% 80% 0% D. 2,500/μL 40% 50% 0% 10% 0%
C Normal WBC counts for CSF are 0-5/μL for adults and 0-30/μL for children. Neutrophils predominate the differential in bacterial meningitis, while lymphocytes predominate in viral meningitis. Hemorrhage and traumatic tap will also cause increased PMNs, and WBC counts should be corrected using the CSF RBC count.
Which of the following conditions is most often associated with a pleural fluid glucose below 30 mg/dL? A. Diabetes mellitus B. Pancreatitis C. RA D. Bacterial pneumonia
C Normal pleural fluid has the same glucose concentration as plasma. Hyperglycemia is the only condition that is associated with a high pleural fluid glucose. Low glucose levels (<60 mg/dL) may be seen in infection, malignancy, and rheumatic diseases. However, glucose levels are lowest (often below 30 mg/dL) and are a constant finding when rheumatoid disease affects the lungs. Pancreatitis causes an exudative peritoneal and pleural effusion with an elevated peritoneal fluid amylase (without a low glucose).
The term used to denote a high WBC count in the CSF is: A. Empyema B. Neutrophilia C. Pleocytosis D. Hyperglycorrhachia
C Pleocytosis refers to an increase in WBCs within the CSF. Bacterial meningitis causes a neutrophilic pleocytosis, viral meningitis a lymphocytic pleocytosis, and tuberculous and fungal meningitis a mixed-cell pleocytosis. Other causes of pleocytosis include multiple sclerosis, cerebral hemorrhage or infarction, and leukemia.
A synovial fluid sample is examined using a polarizing microscope with a red compensating filter. Crystals are seen that are yellow when the long axis of the crystal is parallel to the slow vibrating light. When the long axis of the crystal is perpendicular to the slow vibrating light, the crystals appear blue. What type of crystal is present? A. Calcium oxalate B. Calcium pyrophosphate C. Uric acid D. Cholesterol
C Polarized microscopy with a red compensating filter differentiates uric acid and pseudogout crystals. When the long axis of uric acid needles is parallel to the slow vibrating light, the crystals appear yellow. When the long axis is perpendicular to the slow vibrating light, the crystals appear blue. Calcium pyrophosphate gives the reverse effect.
Which of the following conditions is most likely to cause a falsely low L/S ratio? A. The presence of PG in amniotic fluid B. Freezing the specimen for one month at -20°C C. Centrifugation at 1,000 × g for 10 minutes D. Maternal diabetes mellitus
C Pulmonary surfactants are largely present in the form of lamellar bodies and can be lost by centrifuging the amniotic fluid at high g force. Centrifuge speed should be the minimum required to spin down cells (450 g for 10 minutes at 4°C). Samples that cannot be measured immediately should be refrigerated or frozen. Samples are stable for up to 3 days at 2°C-8°C and for months when frozen at -20°C or lower. Meconium and blood may also introduce errors when measuring the L/S ratio. Blood has an L/S ratio of approximately 2:1 and will falsely raise the L/S ratio when fetal lungs are immature and depress the L/S ratio when fetal lungs are mature.
In which condition is the synovial fluid glucose most likely to be within normal limits? A. Septic arthritis B. Inflammatory arthritis C. Hemorrhagic arthritis D. Gout
C Synovial fluid glucose is normally less than 10 mg/dL below the serum glucose, and should be collected after an 8-hour fast to ensure that the fluid and plasma are equilibrated. In septic arthritis, the glucose level is often more than 40 mg/dL below the serum level and about 25-40 mg/dL lower in inflammatory arthritis, which includes gout. Osteoarthritis and hemorrhagic arthritis are not usually associated with low joint fluid glucose.
The diagnosis of multiple sclerosis is often based upon which finding? A. The presence of elevated protein and low glucose B. A decreased IgG index C. The presence of oligoclonal bands by electrophoresis D. An increased level of CSF β microglobulin
C The total CSF protein is increased in less than half of persons with MS. The IgG index is increased in 80% or more of MS cases. While the IgG index is sensitive, it is increased in many other disorders. The presence of oligoclonal banding (two or more discrete bands in the gamma zone following electrophoresis) is seen in 90% of persons with MS, and in few other diseases. While not entirely definitive, it is the single most effective laboratory test for the diagnosis of MS. When performing CSF electrophoresis, the serum pattern must be compared to the CSF pattern. At least some of the oligoclonal bands must not be found in the serum pattern for the test to be considered positive. Beta-2 microglobulins are increased in CSF in inflammatory diseases (especially malignant diseases).
Which of the following statements regarding pregnancy testing is true? A. β Subunits of human chorionic gonadotropin (hCG), thyroid-stimulating hormone (TSH), and follicle-stimulating hormone (FSH) are very similar B. Antibodies against the β subunit of hCG cross-react with luteinizing hormone (LH) C. A false-positive result may occur in patients with heterophile antibodies D. Serum should not be used for pregnancy tests because proteins interfere
C The α subunit of hCG is very similar to the α subunit of TSH and FSH and identical to LH. Although the β subunits of hCG and LH are very similar, antibodies can be made to the β subunit of hCG that do not cross-react with LH or other pituitary hormones. Most enzyme immunoassay (EIA) methods utilize two monoclonal antibodies against different sites of the hCG molecule. One antibody is specific for the carboxy terminal end of the β chain, and the other reacts with the α chain, resulting in a positive test only when intact hCG is present. Because monoclonal antibodies are derived from mouse hybridomas, rare false positives may occur in patients who have antimouse Ig antibodies. Although the test can detect lower levels of hCG, 25 mIU/mL is the positive cutoff point for pregnancy. Serum is preferred over urine because serum levels are more consistently above the cutoff point than random urine in very early pregnancy.
Which of the following laboratory results is characteristic of a transudative fluid? A. SG = 1.018 B. Total protein = 3.2 g/dL C. LD fluid/serum ratio = 0.25 D. Total protein fluid/serum ratio = 0.65
C Transudative fluids are distinguished from exudative fluids by the physical appearance, cellularity, SG, total protein, LD, cholesterol, and bilirubin. Exudative fluids have a fluid:serum LD ratio greater than 0.6 caused by release of the enzyme from inflammatory or malignant cells. Exudative fluids have a total protein greater than 3.0 g/dL, SG greater than 1.015, fluid:serum total protein ratio greater than 0.6, cholesterol greater than 60 mg/dL (fluid:serum ratio > 0.3) and fluid:serum bilirubin ratio greater than 0.6. Exudates are caused by infection, infarction, malignancy, rheumatoid diseases, and trauma.
Which observation is least useful in distinguishing a hemorrhagic serous fluid from a traumatic tap? A. Clearing of fluid as it is aspirated B. Presence of xanthochromia C. The formation of a clot D. Diminished RBC count in successive aliquots
C Xanthochromia indicates either an exudative process or prior traumatic tap. Hemorrhagic pleural fluids usually have RBC counts greater than 100,000/μL and are usually caused by lung neoplasms. Clearing of fluid or diminished RBC counts in successive tubes favors a diagnosis of a traumatic tap. A clot may form in a hemorrhagic fluid or following a traumatic tap. However, a transudative fluid will not clot.
Which of the following findings is consistent with a subarachnoid hemorrhage rather than a traumatic tap? A. Clearing of the fluid as it is aspirated B. A clear supernatant after centrifugation C. Xanthochromia D. Presence of a clot in the sample
C Xanthochromia is pigmentation of CSF caused by subarachnoid hemorrhage, high CSF protein, free hemoglobin, or bilirubin. The bilirubin may be caused by hepatic disease, CNS hemorrhage, or prior traumatic tap. In subarachnoid hemorrhage, the fluid will be pink if the RBC count is greater than 500/μL. It will turn orange as RBCs lyse in the first few hours, and will turn yellow after about 12 hours. Granulocyte infiltration occurs immediately after a subarachnoid hemorrhage, and disappears after 24 hours. It is followed by an increase in macrophages, showing evidence of erythrophagocytosis that remains for up to 2 weeks. After subarachnoid hemorrhage, D-dimer is present in CSF, and can be used to distinguish between a traumatic tap and subarachnoid hemorrhage.
Which of the following statements regarding routine microbiological examination of CSF is true? A. A Gram stain is performed on the CSF prior to concentration B. The Gram stain is positive in fewer than 40% of cases of acute bacterial meningitis C. India ink and acid fast stains are indicated if neutrophilic pleocytosis is present D. All CSF specimens should be cultured using sheep blood agar, chocolate agar, and supplemented broth
D A culture should be performed on the sediment of the third aliquot of the CSF after it is centrifuged. Blood and chocolate agar and anaerobic broth should always be used, and, if sterile, held a minimum of 3 days. Blood cultures should be done since septicemia occurs in about one-half of bacterial meningitis cases. A Gram stain is always performed using sediment of the CSF because it is positive in more than 70% of acute bacterial meningitis cases. India ink, acid-fast, and wet preparations may be ordered if an absolute monocytosis is present.
SITUATION: What is the most likely cause of the following CSF results? CSF glucose 20 mg/dL; CSF protein 200 mg/dL; CSF lactate 50 mg/dL (reference range 5-25 mg/dL) A. Viral meningitis B. Viral encephalitis C. Cryptococcal meningitis D. Acute bacterial meningitis
D Acute bacterial meningitis causes increased production of immunoglobulins in CSF. Glucose levels are below normal (<40 mg/dL) due to consumption by PMNs and bacteria. Lactate levels rise due to increased pressure and hypoxia (>35 mg/dL being correlated with bacterial meningitis). When associated with increased PMNs and LD, these findings point to bacterial meningitis.
Which of the following conditions is most often associated with normal CSF glucose and protein? A. Multiple sclerosis B. Malignancy C. Subarachnoid hemorrhage D. Viral meningitis
D In viral (aseptic) meningitis, the CSF glucose is usually above 40 mg/dL and the total protein is normal or slightly increased. Some types of viral meningitis can cause a low glucose, which makes the differentiation of bacterial and viral meningitis difficult. Low CSF glucose and elevated total protein are also seen in malignancy, subarachnoid hemorrhage, and some persons with multiple sclerosis. Low glucose in malignancy and multiple sclerosis results from increased utilization. Glucose is reduced in subarachnoid hemorrhage due to release of glycolytic enzymes from RBCs. All three conditions result in high CSF protein, but multiple sclerosis is associated with an increased IgG index owing to local production of IgG.
Which of the following conditions is associated with a chylous effusion? A. Necrosis B. Pulmonary infarction or infection C. Systemic lupus erythematosus or rheumatoid arthritis D. Lymphatic obstruction
D Malignancy, pulmonary infarction, SLE, and RA are characterized by inflammation with increases in protein, WBCs, and LD. Exudates can also be caused by tuberculosis, pancreatitis, and lymphoma. Lymphatic obstruction is often associated with lymphoma and other malignancies that block the flow of lymph into the azygous vein. This causes a chylous effusion. Chylous effusions are also caused by traumatic injury to the thoracic duct. Necrosis causes a pseudochylous effusion. This resembles a chylous effusion in appearance but has a foul odor. Chylous fluids contain chylomicrons, stain positive for fat globules, show lymphocytosis, and have a triglyceride concentration over twofold higher than plasma (or > 110 mg/dL). Pseudochylous effusions are characterized by mixed cellularity and elevated cholesterol.
Neutrophilic pleocytosis is usually associated with all of the following except: A. Cerebral infarction B. Malignancy C. Myelography D. Neurosyphilis
D Neutrophils may appear in CSF from many causes, making it necessary to correlate results of chemical assays with hematologic findings. Low glucose and high protein occur in both malignancy and bacterial meningitis. Tumor markers and lactate may be helpful in distinguishing malignancy from bacterial meningitis. In neurosyphilis, there is usually an absolute lymphocytosis, increased total protein and IgG index.
Which of the following characteristics is higher for synovial fluid than for the serous fluids? A. SG B. Glucose C. Total protein D. Viscosity
D Synovial fluid has approximately the same SG and glucose as plasma and the serous fluids but is far more viscous due to a high content of mucoprotein (hyaluronate) secreted by the synovium. Viscosity is estimated by pulling the fluid from the tip of a syringe or pipet. Normal fluid gives a string longer than 4 cm. Low viscosity indicates inflammation. The total protein of synovial fluid is usually lower than serous fluids, the upper reference limit being 2.0 g/dL.
In which condition is the pleural fluid pH likely to be above 7.3? A. Bacterial pneumonia with parapneumonic exudate B. Rheumatoid pleuritis C. Esophageal rupture D. Pneumothorax
D The pH of pleural fluid is approximately 7.64, and values below 7.30 are usually associated with a poorer prognosis and usually require drainage. Esophageal rupture produces the lowest pH with values in the range of 6.0-6.3. In addition, pleural fluid pH is low in rheumatoid disease involving the lungs and pleura, some malignancies, and SLE. Low pH and glucose in pleural fluid are seen in lung abscess and exudative bacterial pneumonia (called parapneumonic effusion). Pneumothorax results from air entering the pleural space and does not produce a low pH.
