Chemistry

What additional fraction would be seen if plasma rather than serum was subjected to electrophoresis:

Fibrinogen Feedback Fibrinogen present in plasma would form a band between the beta and gamma globulins. Question Difficulty: Level 2

A patient presents with an elevation of unconjugated bilirubin, normal serum alkaline phosphatase, normal liver enzymes, and no bilirubin in the urine. This combination would suggest:

Increased rate of hemolysis Feedback Unconjugated bilirubin is a byproduct of RBC breakdown, or hemolysis. It would be expected to see an increase in unconjugated bilirubin when hemolysis is occuring at an increased rate. The liver enzymes would not remain at normal levels if there were a viral infection of the liver, chemical damage to the liver, or obstruction of bile ducts. Question Difficulty: Level 6

Which of the following is necessary for the absorption of Vitamin B12:

Intrinsic factor Feedback Intrinsic factor is necessary for the proper absorption of vitamin B12. With a deficiency of intrinsic factor, individuals can develop a megaloblastic anemia if their bodies become deficient in vitamin B12, which plays a large role in cellular nuclear development. Question Difficulty: Level 5

A zinc deficiency in the elderly is often caused by:

Decreased intake and absorption Feedback Some elderly individuals can have poor dietary habits which can lead to decreased nutrient absorption, including zinc. Question Difficulty: Level 4

A 45-year-old male of average height and weight had a serum creatinine of 1.5 mg/dL and urine creatinine was 120 mg/dL; the total volume of urine collected over a 24-hour period was 1,800 mL. Calculate the creatinine clearance for this patient in mL/min.`

100 Feedback The creatinine clearance for this patient is 100 mL/min. Creatinine clearance values are calculated using the following equation: Creatinine Clearance (mL / min) = (Urine Creatinine / Serum Creatinine) x Urine Volume (mL) / [ time (hr) x 60 ] For this patient Creatinine clearance (mL/min)= (120/1.5) x (1800 / [24 x 60]) 80 x 1800/1440, which is 80 x 1.25, or 100 mL/min` Question Difficulty: Level 6

Which of the following would be considered a normal cerebrospinal fluid glucose if the serum glucose is 70 mg/dl?

45 mg/dl Feedback As a general rule, CSF glucose is about two thirds of the serum glucose measured in a normal adult. Question Difficulty: Level 4

Which of the following statements is FALSE regarding troponin?

It rises much sooner after an MI than CK-MB Feedback Troponin is potentially more specific for myocardial damage than CK-MB and stays elevated longer. It may eventually replace CK-MB as the standard marker of myocardial damage. In addition, troponin T has been known to be elevated in the setting of even mild degrees of renal failure. Troponin and CK-MB both tend to rise approximately 3 hours after a MI (hence why the correct answer is "A", since it is false); however, troponins can stay elevated up to 2 weeks as CK-MB tends to return to baseline around 36 hours. Question Difficulty: Level 6

Match the type of endocrine dysfunction with the appropriate organ:

Target gland Primary Pituitary gland Secondary Hypothalamus Tertiary Feedback Primary- Target glands (such as thymus, thyroid, parathyroid, etc.) Secondary- Pituitary gland Tertiary- Hypothalamus Question Difficulty: Level 6

Deviations from Beer's Law are caused by:

stray light Feedback Beer's law is based on the fact that absorbance is directly proportional to the concentration of a solution. Therefore, stray light can alter the absorbance results in this type of assay. Question Difficulty: Level 5

Gestational diabetes is diagnosed with the same testing and criteria used for the diagnosis of diabetes for a nonpregnant adult.

False Feedback The diagnostic testing used for diabetes during pregnancy is different. There are different screening tests for gestational diabetes and an OGTT is used to confirm diagnosis. Question Difficulty: Level 2

Which of the following statements best describe HbA1C?

A glycated protein that is an index of carbohydrate management over 2 - 3 months. Feedback HbA1C is the nonenzymatic addition of a glucose molecule to Hb A. After a rearrangement, the addition is irreversible. The concentration of HbA1C relates to the individual's average glucose concentration over 2 - 3 months. Question Difficulty: Level 2

The accuracy of an immunoassay is its ability to discriminate between results that are true positives and results that are true negatives. Two parameters of test accuracy are specificity and sensitivity. Which of these statements apply to an immunoassay with high specificity, but low sensitivity?

Accurately identifies the absence of disease Has few false-positives Feedback A test with high specificity accurately detects the absence of disease. The more specific a test is, the fewer false-positive results will occur. A test with high sensitivity accurately identifies the presence of disease. The more sensitive a test, the fewer false-negative results it produces. In the case stated in this question, the immunoassay has high specificity, so it has few false-positives and will accurately detect those individuals who do not have the disease or condition that is being tested for. However, the test has low sensitivity, so it may not identify all individuals who actually have the disease; it may produce many false-negative results. Question Difficulty: Level 7

Which one of the following usually shows a decrease during an acute phase response?

Albumin Feedback Albumin is a "negative" acute phase protein since it is found in decreased levels during acute phase response. Alpha-1-antitrypsin, fibrinogen, and ceruloplasmin are all "positive" acute phase proteins that are found in increased levels during acute phase response. Question Difficulty: Level 6

Which is true concerning apolipoproteins?

Apolipoproteins are essential for lipid metabolism. Feedback Apolipoproteins are essential for lipid metabolism; this is the only true statement of the three choices. The apolipoproteins on a particle contribute to the identity of the particle; not all lipoprotein particles contain the same apolipoproteins. Apolipoproteins are not atherogenic. Question Difficulty: Level 3

All of the following are sources of serum alkaline phosphatase except:

Brain Feedback The source of elevated alkaline phosphatase can be identified by electrophoresis of tissue specific isoenzymes at alkaline pH. Liver and bone are the most commonly identified isoenzymes. Question Difficulty: Level 3

After complaining to her physician about persistent pelvic pain and abdominal pressure, Mrs. Smith, had laboratory testing ordered. Since her physician would like to rule-out ovarian cancer, which of the following assays would be most helpful?

CA125 Feedback CA125 is an antigen present on approximately 80% of ovarian carcinomas. CA125 is often elevated in patients with ovarian cancer and its concentration follows the course of disease. It is important to note that CA125 is not completely specific for ovarian carcinomas, it can be found in increased levels in other cancers including endometrial, pancreatic, lung, breast, and colon cancer, along with other conditions such as pregnancy. CEA (carcinoembryonic antigen) is typically utilized for colon cancer screening and prognosistic purposes. CA19-9 is typically found in increased levels in conditions such as gastrointestinal adenocarcinoma and pancreatic cancers. Finally, PSA (prostate specific antigen) is specific to the prostate gland. This tumor marker is increased in conditions such as prostate cancer and prostatitis. Question Difficulty: Level 3

Which of the following are markers of myocardial necrosis but are not widely measured in evaluating chest pain and ACS due to the labor-intensive method that is needed to measure them?

CK-MB isoforms Feedback CK-MB isoforms are markers of myocardial necrosis, but are not widely measured in evaluating chest pain and ACS due to the labor-intensive method that is needed to measure them. Detection of CK-MB isoforms requires a special electrophoresis technique. Question Difficulty: Level 5

Ionized calcium is most commonly measured using which of the following method:

Calcium ion selective electrodes Feedback Ion Selective Electrodes, or ISEs, are the most common methodology used to detect calcium in various laboratory instruments. A calcium ISE has a PVC membrane, which is impregnated with an organic molecule that selectively binds and transports Ca++ ions, and contains an internal solution with a fixed concentration of calcium chloride - added to the KCl / AgCl solution of the internal reference system. Question Difficulty: Level 3

The buffering capacity of blood is maintained by a reversible exchange process between bicarbonate and:

Chloride Feedback Bicarbonate and Chloride form an exchanger to help regulate and buffer the body's pH. Question Difficulty: Level 3

Which of the following lipoproteins will form a creamy layer at the top of stored, non-fasting plasma specimens?

Chylomicrons Feedback Normally absent in fasting specimens, chylomicrons will form a creamy layer at the top of stored, non-fasting plasma specimens. Chylomicron particles are 98% lipid, 90% of which are exogenous triglycerides, which means the triglycerides originate from sources outside the body (i.e., food sources). They are the least dense of the lipoprotein particles; therefore, when a non-fasting plasma is stored, chylomicrons will rise to the top. Question Difficulty: Level 3

An elevated level of which of the following hormones will inhibit pituitary secretion of adrenocorticotropic hormone (ACTH)?

Cortisol Feedback Cortisol is part of the negative feedback mechanism for ACTH. So elevated levels of cortisol stimulate the pituitary gland to inhibit the secretion of ACTH. Question Difficulty: Level 4

A 64-year old man lost 15 pounds, became weaker, and his face became fuller with a ruddy complexion. His laboratory tests revealed: Serum cortisol 8 AM: 880 nmol/L, 138-635 nmol/L (reference range) 4 PM: 828 nmol/L, 83-414 nmol/L (reference range) After these results, an overnight dexamethasone suppression test gave a cortisol level of 773 nmol/L. The MOST probable diagnosis for this patient is:

Cushing's Syndrome Feedback Cushing's syndrome is a hormonal disorder caused by the effects of an individual having high levels of cortisol. One of the signs of this condition is skin, which becomes fragile and thin and a rounding, or fullness of the face. More than one test is performed to diagnose Cushing's syndrome and include: the 24-hour urinary free cortisol test, measurement of day and night cortisol levels, and the low-dose dexamethasone suppression test. Cortisol production is normally suppressed at night, but in Cushing's syndrome, this suppression doesn't occur. If the cortisol level is more than 50 nmol/L, Cushing's syndrome is suspected. In the dexamethasone suppression test, cortisol signals the pituitary to release less ACTH, so the normal response after taking dexamethasone is a decrease in blood and urine cortisol levels; if cortisol levels do not decrease (such as in this case), Cushing's syndrome is suspected. Question Difficulty: Level 3

Which of the following is true of genotype screening in pharmacogenomics?

Genotyping does not take into account drug interactions which can affect metabolism. Feedback Genotyping, while more robust and definitive, cannot factor in environmental or health variables that could affect drug metabolism. Probe drug analysis does factor in these variables, but it is more complex and tedious. Genotyping typically involves measuring many polymorphisms. For example, a laboratory that offers CYP2D6 profiling may measure twelve of the most common and significant mutation sites on this enzyme. Question Difficulty: Level 6

Which enzyme is responsible for the conjugation of bilirubin?

Glucuronyl transferase Feedback Glucuronyl transferase is responsible for the conjugation of bilirubin in the liver. When deficiencies exist of this important enzyme, disease states can occur. A deficiency in glucuronosyl transferase is thought to be the cause of Gilbert's syndrome (unconjugated hyperbilirubinemia) and Crigler-Najjar syndrome, where this enzyme is completely or mostly absent. Question Difficulty: Level 4

Six months ago, a 55-year-old female had a fasting plasma glucose (FPG) greater than 200 mg/dL on two occasions. She was diagnosed as having type 2 diabetes and treatment was started. Along with routine FPG's which of the following tests would most likely be used to monitor glycemic control?

HbA1C Feedback FPG is performed to monitor diabetes, often weekly or even daily. The ADA also recommends that a HbA1C be tested at least twice a year to monitor long-term glycemic control. Question Difficulty: Level 1

A specimen for potassium was drawn in a tube without anticoagulant at 6 AM during a traumatic patient stick. The results were 6.0 mmol/L. Why are the results elevated?

Hemolysis of the RBC's Feedback During a traumatic stick, the red blood cells often become severly hemolyzed, or break apart, during the blood collection process. When this occurs, the potassium will leak out of red blood cells into the plasma causing a falsely elevated potassium result. Question Difficulty: Level 2

A critically ill 86-year-old female was admitted to the intensive care unit (ICU) after arriving at the emergency department with symptoms that included shortness of breath and fever. Her temperature was 39°C (102°F) and pulse rate 110/minute. A white blood count was ordered and was elevated at 15.0 x 109/L. The differential showed an increase in segmented and immature neutrophils. Other testing was ordered after admission to ICU, including a procalcitonin (PCT). The result was 2.15 ng/mL (Reference value for normal at the 95th percentile is <0.05 ng/mL). Given the clinical assessment and laboratory test results, what may the increased procalcitonin indicate?

High risk of severe sepsis/septic shock Feedback The increased PCT may indicate a high risk of severe sepsis/septic shock. PCT significantly increases during severe sepsis and septic shock, making it a valuable marker for evaluating prognosis and monitoring antibiotic therapy. If a critically ill patient's PCT level is evaluated in conjunction with clinical assessments, the risk for progression to severe sepsis and septic shock can be assessed on the first day of admission to the ICU. Question Difficulty: Level 2

Which of the following is the most common technique that is used by clinical laboratories for therapeutic drug monitoring?

Immunoassay Feedback Immunoassay is the most common technique that is used by clinical laboratories for therapeutic drug monitoring. Most of the drugs commonly assessed with TDM can be measured on analytical platforms which utilize antibodies (in some form) for detection. Antibodies can be developed that recognize drugs. Although most drugs are much too small to evoke an immune response, scientists can conjugate drugs to immunogenic proteins to produce antibodies that recognize drug-specific epitopes. Question Difficulty: Level 4

Which of the following hormones is mainly responsible for the entry of glucose into the cell for energy production?

Insulin Feedback Insulin is the hormone that is mainly responsible for the entry of glucose into the cell for energy production Glucagon and epinephrine promote glycogenolysis, conversion of glycogen to glucose, which increases plasma glucose. Cortisol, along with glucagon, increases gluconeogenesis, formation of glucose from noncarbohydrates, which also raises plasma glucose concentration. Question Difficulty: Level 4

Which of the following is used primarily for the treatment of manic-depression:

Lithium Feedback Lithium is commonly used in the treatment of manic depressive patients. Lithium exerts a dual effect on receptors for the neurotransmitter glutamate; acting to keep the amount of glutamate active between cells at a stable, healthy level, neither too much nor too little. This allows for a mood stabilization for these patients. Question Difficulty: Level 2

Which of the following conditions is most likely when an oligoclonal band is seen in CSF electrophoresis without a corresponding serum peak?

Multiple sclerosis Feedback Oligoclonal bands are found in the CSF of most patients with multiple sclerosis. Question Difficulty: Level 5

Creatinine excretion correlates best with which of the following parameters:

Muscle mass Feedback Creatinine excretion is related to muscle mass and is fairly constant from day to day for a given individual. Question Difficulty: Level 3

The measurement of total glycosylated hemoglobin A1c is an effective means of assessing the average blood glucose levels:

Over the past 2-3 months Feedback The concentration of hemoglobin A1c is directly proportional to the average plasma glucose level that the RBCs are exposed to during their 120 day life span. The glycosylated hemoglobins result from glycosylation of serine, asparagine, and hydroxylysine residues in hemoglobin. There are three glycosylated hemoglobins: Hb A1a, Hb A1b, and Hb A1c, of which Hb A1c constitutes 80%. Most methods measure total gycosylated hemoglobin, which has a high degree of correlation to Hb A1c, and may be reported as such after making the appropriate conversion. Question Difficulty: Level 1

Of the three laboratory tests that are listed, which has proven to be most effective for early differentiation of systemic inflammatory response syndrome (SIRS) from sepsis due to its increase following infection and higher specificity?

Procalcitonin (PCT) Feedback PCT usually rises within 3-6 hours of infection. CRP also increases rapidly following infection, but is not as specific for infection as PCT. A rise in CRP could also occur with SIRS. Lactic acid is usually used to detect and monitor impaired circulation and tissue oxygenation in critically ill patients. Question Difficulty: Level 6

A patient who previously had an hs-CRP of 4 mg/L was put on statin and daily aspirin medication. She returns to the laboratory a month later, and her repeat hs-CRP is 2.3 mg/L. Which of the following is the most likely reason for the decrease in the test value?

The medications lowered the hs-CRP value. Feedback The medications (a cholesterol-lowering statin and the anti-inflammatory aspirin) can lower hs-CRP. A single hs-CRP value does not neccessarily reflect risk. It is not likely that the test was performed incorrectly the first time and the initial hs-CRP test result was not indicative of an infection. Question Difficulty: Level 2

Which of the following factors would not affect an orally-administered drug's absorption and/or distribution in the body?

The position of the patient when the drug is taken (sitting vs. standing) Feedback The physical position of the patient when the drug is taken (sitting vs. standing) would not affect an orally-administered drug's absorption and/or distribution in the body. Regional blood flow will affect drug distribution because the drug is transported in the blood. Reduced area blood flow can be seen in diabetics, and enhanced blood flow can be seen in tumors. Drug kinetics and dispositions change throughout life. In general, metabolism of drugs is reduced in the elderly. In the diseased gut, an orally-administered drug may not be absorbed as expected. Question Difficulty: Level 2

A patient suffering from Celiac disease and Crohn disease (both inflammatory conditions of the GI tract) is given a new oral medication that has a narrow therapeutic window. Which of the following would be true?

Therapeutic drug monitoring (TDM) would be helpful to see how much drug has been absorbed. Feedback TDM would be helpful to see how much drug has been absorbed. Blood collection for the TDM test should occur at least one hour after the administration of the oral drug. Measuring the serum level of the drug 15 minutes after the oral dose has been given is not sufficient time to allow for absorption Celiac disease and Crohn's disease are both inflammatory conditions of the GI tract that can cause decreased absorption. Although an IV drug may be preferred, not all drugs are available as IV solutions; until low absorption is confirmed, an oral drug may be tried. The patient may or may not have poor absorption, but toxicity could still occur regardless of absorption. For example, toxicity to the GI tract could ensue without the drug ever being absorbed. Question Difficulty: Level 2

Which of the following statements is true regarding CYP450 enzymes?

They are involved in hormone synthesis and breakdown, cholesterol synthesis, vitamin D metabolism, and drug and toxic substance breakdown. Feedback CYP450s They are involved in hormone synthesis and breakdown, cholesterol synthesis, vitamin D metabolism, and drug and toxic substance breakdown. CYP450s are the major enzymes involved in drug metabolism, which makes this system important in medical practice to ensure proper patient dosing and response based upon an individual's genetic CYP450 makeup. CYP450s are the primary, but not the only, hepatic enzymes involved in drug metabolism. There are many CYP450s (at least 18 with possible isoenzymes of each). CYP450s are found primarily in the liver. They accept a variety of substrates and so are able to metabolize diverse compounds. Each CYP450 can metabolize several different drugs, making the CYP450 family versatile and able to address the wide range of chemical substances encountered by an individual. Question Difficulty: Level 2

Circulating organic iodine is found primarily in the form of:

Thyroxine Feedback Iodine circulates as thyroxine (T4) and to a lesser extent as Triiodothyronine (T3). Question Difficulty: Level 5

Which one of the following is the MOST specific biochemical marker of myocardial infarction?

Troponin Feedback Troponin is a very specific biomarker that is released during cardiac injury or stress. CK is found not only in cardiac tissue, but also in muscle and brain tissue. LD levels can be elevated in cardiac events, tissue breakdown, and hemolysis. Myoglobin is elevated when muscle tissue is damaged and is not specific for the heart muscle. Question Difficulty: Level 3

HbA1C measurements are NOT ordinarily used to monitor long-term diabetic control in a diabetic with sickle cell anemia.

True Feedback In sickle cell anemia, rapid hemoglobin turnover may be present. HbA1C and other glycated hemoglobin assays are not valid in rapid hemoglobin turnover and in abnormal hemoglobin conditions. Fructosamine measurements can be used because of shorter half life of albumin. Question Difficulty: Level 5

Which of the following proteins has the FASTEST electrophoretic mobility?

albumin Feedback The serum proteins can be separated into five fractions by serum protein electrophoresis. In order of decreasing electrophoretic mobility these fractions are the: serum albumin, alpha-1 globulins, alpha-2 globulins, beta globulins, and gamma globulins. Question Difficulty: Level 3

Which of the following enzymes is NOT used to determine hepatobiliary dysfunction?

aldolase Feedback Aldolase is an enzyme that cleaves an aldol that aids in the conversion of glucose to energy. Aldolase is associated with the muscles, and is currently used in the monitoring of patients with muscular dystrophy and a few other rare conditions affecting skeletal muscles. A serum ALP measurement's most useful clinical attribute is its sensitivity in distinguishing hepatobiliary disease. Gamma-glutamyltransferase, or GGT, is elevated in liver diseases affecting the biliary system. Serum concentrations of 5'-nucleotidase, or 5NT, reflect hepatobiliary disease with high specificity as well. Question Difficulty: Level 5

Which of the following choices is correct when describing the principles of competitive radioimmunoassay procedures?

antibody will react equally with labeled and unlabeled antigen Feedback In radioimmunassay, a fixed concentration of labeled antigen is incubated with a constant amount of antiserum such that the concentration of antigen binding sites on the antibody is limiting. If unlabeled antigen is added to this system, there is competition between labeled antigen and unlabeled antigen for the limited and constant number of binding sites on the antibody, and thus the amount of labeled antigen bound to antibody will decrease as the concentration of unlabeled antigen increases. Question Difficulty: Level 5

A mutation in a CYP450 enzyme that causes increased enzyme activity would

be a polymorphism if the mutation was present in at least 1% of the population. require that the patient with this mutation is given greater than the standard dose of a drug if it is metabolized by this enzyme. lead to lower drug response with standard doses. All of the above Feedback All of the above answers are true. A normal (wild-type) allele of a CYP450 gene displays normal metabolic activity, whereas some of the variant forms have enhanced or diminished activity. If the variation of the gene (allele) affects at least 1% of the population, it is considered a polymorphism. If a patient has a mutation in a CYP450 enzyme that causes increased enzyme activity, he/she will probably need a higher dose than the standard dose of any drug that is metabolized by this enzyme. If standard doses are given to a patient that has increased enzyme activity, the drug will probably not achieve the desired affect. Question Difficulty: Level 2

In patients with suspected primary hypothyroidism associated with Hashimoto's thyroiditis, one would expect the following laboratory test results: T4 ___? TSH ___? TRH stimulation ___?

decreased, increased, increased Feedback In Hashimoto's, antibodies react against proteins in the thyroid gland, causing gradual destruction of the gland itself, and making the gland unable to produce the thyroid hormones the body needs. Therefore the T4 is decreased, but the TSH is increased since the pituitary gland is attempting to stimulate the failing thyroid gland. The TRH stimulation is increased since the pituitary gland is working and is able to produce elevated levels of TSH upon TRH stimulation. Question Difficulty: Level 4

Bioavailability of an oral drug refers to the

fraction of the drug that is absorbed into systemic circulation Feedback The bioavailability of an oral drug is the fraction of the drug that is absorbed into systemic circulation. The bioavailability of a drug is calculated by comparing the area under the plasma concentration-time curve of an equivalent dose of the intravenous form and the oral form of the drug. For oral drugs to be effective, bioavailability typically should be greater than 70%. Question Difficulty: Level 3

Which of the following substances is conjugated with the "indirect" bilirubin to form "direct" bilirubin?

glucuronic acid Feedback Indirect bilirubin, also known as unconjugated bilirubin, is conjugated with two molecules of glucuronic acid to form direct, or conjugated bilirubin, which is water-soluble. Ascorbic acid, also known as vitamin C, uric acid, or salicylic acid do not conjugate with bilirubin. Question Difficulty: Level 3

An electrophoretic separation of lactate dehydrogenase isoenzyme that demonstrates elevation in LD-1 greater than LD-2 could be indicative of:

myocardial infarction Hemolysis A and B Feedback LD-1 and LD-2 are both increased during myocardial infarction since they are both present in heart muscle. Hemolysis, both in vivo and in vitro, can also cause elevations in LD-1 and LD-2. Also in normal conditions, LD-2 is present in higher concentrations than LD-1. The reverse is true in myocardial infarction and during states of hemolysis. This term is referred to as the LD flip. Pancreatitis does cause increased levels of LD, but the LD-4 type is the most affected in this condition. Question Difficulty: Level 5