Medical Laboratory Science Review Harr. - 3.3 Immunology and Serology: Infectious Disease

Which increase in antibody titer (dilution) best indicates an acute infection? A. From 1:2 to 1:8 B. From 1:4 to 1:16 C. From 1:16 to 1:256 D. From 1:64 to 1:128

C A fourfold (2 tube) or greater increase in antibody titer is usually indicative of an acute infection. Although answers A and B show a fourfold rise in titer, answer C shows a 16-fold rise in titer and is the most definitive. In most serological tests, a single high titer is insufficient evidence of acute infection unless specific IgM antibodies are measured because age, individual variation, immunologic status, and history of previous exposure (or vaccination) cause a wide variation in normal serum antibody titers

A biological false-positive reaction is least likely with which test for syphilis? A. VDRL B. Fluorescent T. pallidum antibody absorption test (FTA-ABS) C. RPR D. All are equally likely to detect a false-positive result

. B The FTA-ABS test is more specific for T. pallidum than nontreponemal tests such as the VDRL and RPR and would be least likely to detect a biological false-positive result. The FTA-ABS test uses heat-inactivated serum that has been absorbed with the Reiter strain of T. pallidum to remove nonspecific antibodies. Nontreponemal tests have a biological false-positive rate of 1%-10%, depending upon the patient population tested. False-positive findings are caused commonly by infectious mononucleosis (IM), SLE, viral hepatitis, and human immunodeficiency virus (HIV) infection.

. Which tests are considered confirmatory tests for HIV? A. ELISA and rapid antibody tests B. Western blot test, HIC-1,2 differentiation assays, and polymerase chain reaction C. Culture, antigen capture assay, polymerase chain reaction D. Reverse transcriptase and mRNA assay

. B Western blot, and PCR tests are generally used as confirmatory tests for HIV. An HIV-1,2 differentiation assay is recommended as the confirming procedure following a reactive 4th generation HIV assay. PCR, however, is more often used for early detection of HIV infection, for documenting infant HIV infection, and for following antiviral therapy.

What is the most likely interpretation of the following syphilis serological results? RPR: reactive; VDRL: reactive; MHA-TP: nonreactive A. Neurosyphilis B. Secondary syphilis C. Syphilis that has been successfully treated D. Biological false positive

. D A positive reaction with nontreponemal antigen and a negative reaction with a treponemal antigen is most likely caused by a biological false-positive nontreponemal test.

Given a heterophile antibody titer of 224, which of the following results indicate IM? Absorption with Guinea Beef Cells | Absorption with Pig Kidney A. Two-tube titer reduction | Five-tube titer reduction B. No titer reduction | No titer reduction C. Five-tube titer reduction | Five-tube titer reduction D. Five-tube titer reduction | No titer reduction

A. Two-tube titer reduction | Five-tube titer reduction A Antibodies to infectious mononucleosis (nonForssman antibodies) are not neutralized or absorbed by guinea pig antigen (but are absorbed by beef cell antigen). A positive test is indicated by at least a four-tube reduction in the heterophile titer after absorption with beef cells and no more than a three-tube reduction in titer after absorption with guinea pig kidney.

Which test, other than serological markers, is most consistently elevated in viral hepatitis? A. Antinuclear antibodies B. Alanine aminotransferase (ALT) C. Absolute lymphocyte count D. Lactate dehydrogenase

B ALT is a liver enzyme and may be increased in hepatic disease. Highest levels occur in acute viral hepatitis, reaching 20-50 times the upper limit of normal.

Which is the first antibody detected in serum after infection with hepatitis B virus (HBV)? A. Anti-HBs B. Anti-HBc IgM C. Anti-HBe D. All are detectable at the same time

B Antibody to the hepatitis B core antigen (anti-HBc) is the first detectable hepatitis B antibody. It persists in the serum for 1-2 years postinfection and is found in the serum of asymptomatic carriers of HBV. Because levels of total anti HBc are high after recovery, IgM anti-HBc is a more useful marker for acute infection. Both anti-HBc and anti-HBs can persist for life, but only anti-HBs is considered protective.

Which antibody persists in low-level carriers of hepatitis B virus? A. IgM anti-HBc B. IgG anti-HBc C. IgM anti-HBe D. IgG anti-HBs

B IgG antibodies to the hepatitis B core antigen (anti-HBc) can be detected in carriers who are HBsAg and anti-HBs negative. These persons are presumed infective even though the level of HBsAg is too low to detect. No specific B core IgG test is available, however. This patient would be positive in the anti-B core total antibody assay and negative in the anti-HB core IgM test.

What is the most likely cause when a Western blot or ELISA is positive for all controls and samples? A. Improper pipetting B. Improper washing C. Improper addition of sample D. Improper reading

B Improper washing may not remove unbound enzyme conjugated anti-human globulin, and every sample may appear positive

What is the most likely explanation when antibody tests for HIV are negative but a polymerase chain reaction test performed 1 week later is positive? A. Probably not HIV infection B. Patient is in the "window phase" before antibody production C. Tests were performed incorrectly D. Clinical signs may be misinterpreted

B In early seroconversion, patients may not be making enough antibodies to be detected by antibody tests. The period between infection with HIV and the appearance of detectable antibodies is called the window phase. Although this period has been reduced to a few weeks by sensitive enzyme immunoassays, patients at high risk or displaying clinical conditions associated with HIV disease should be tested again after waiting several more weeks.

What substance is detected by the rapid plasma reagin (RPR) and Venereal Disease Research Laboratory (VDRL) tests for syphilis? A. Cardiolipin B. Anticardiolipin antibody C. Anti-T. pallidum antibody D. Treponema pallidum

B. Anticardiolipin antibody B Reagin is the name for a nontreponemal antibody that appears in the serum of syphilis-infected persons and is detected by the RPR and VDRL assays. Reagin reacts with cardiolipin, a lipid-rich extract of beef heart and other animal tissues.

Given a heterophile antibody titer of 224, which of the following results indicate an error in testing? Absorption with Guinea Beef Cells | Absorption with Pig Kidney A. Two-tube titer reduction | Five-tube titer reduction B. No titer reduction | No titer reduction C. Five-tube titer reduction | Five-tube titer reduction D. Five-tube titer reduction | No titer reduction

B. No titer reduction | No titer reduction B An individual with a 56 or higher titer in the presumptive test (significant heterophile antibodies) has either Forssman antibodies, non-Forssman antibodies, or both. A testing error has occurred if no reduction in the titer of antibody against sheep RBCs is observed after absorption because absorption should remove one or both types of sheep RBC agglutinins

Tests to identify infection with HIV fall into which three general classification types of tests? A. Tissue culture, antigen, and antibody tests B. Tests for antigens, antibodies, and nucleic acid C. DNA probe, DNA amplification, and Western blot tests D. ELISA, Western blot, and Southern blot tests

B. Tests for antigens, antibodies, and nucleic acid B Two common methods for detecting antibodies to HIV are the ELISA and Western blot tests. Two common methods for detecting HIV antigens are ELISA and immunofluorescence. Two common methods for detecting HIV genes are the Southern blot test and DNA amplification using the polymerase chain reaction to detect viral nucleic acid in infected lymphocytes

Given a heterophile antibody titer of 224, which of the following results indicate serum sickness? Absorption with Guinea Beef Cells | Absorption with Pig Kidney A. Two-tube titer reduction | Five-tube titer reduction B. No titer reduction | No titer reduction C. Five-tube titer reduction | Five-tube titer reduction D. Five-tube titer reduction | No titer reduction

C. Five-tube titer reduction | Five-tube titer reduction C In serum sickness, antibodies are neutralized by both guinea pig kidney and beef cell antigens, and at least a three tube (eightfold) reduction in titer should occur after absorption with both.

All tubes (dilutions) except the negative control are positive for cold agglutinins. This indicates: A. Contaminated red cells B. A rare antibody against red cell antigens C. The sample was stored at 4°C prior to separating serum and cells D. Further serial dilution is necessary

D Cold agglutinins may be measured in patients who have cold agglutinin disease, a cold autoimmune hemolytic anemia. In such cases, titers can be as high as 106. If all tubes (dilutions) for cold agglutinins are positive, except the negative control, then a high titer of cold agglutinins is present in the sample. Further serial dilutions should be performed.

If only anti-HBs is positive, which of the following can be ruled out? A. Hepatitis B virus vaccination B. Distant past infection with hepatitis B virus C. Hepatitis B immune globulin (HBIG) injection D. Chronic hepatitis B virus infection

D Persons with chronic HBV infection show a positive test result for anti-HBc (IgG or total) and HBsAg but not anti-HBs. Patients with active chronic hepatitis have not become immune to the virus.

Rapid assays for influenza that utilize specimens obtained from nasopharyngeal swabs detect: A. IgM anti-influenza B. IgA anti-influenza C. IgA-influenza Ag immune complexes D. Influenza antigen

D. Influenza antigen D The rapid influenza assays are antigen detection methods. They are designed to detect early infection, before antibody is produced.

A streptozyme test was performed, but the result was negative, even though the patient showed clinical signs of a streptococcal throat infection. What should be done next? A. Either ASO or anti-deoxyribonuclease B (anti-DNase B) testing B. Another streptozyme test using diluted serum C. Antihyaluronidase testing D. Wait for 3-5 days and repeat the streptozyme test

A A streptozyme test is used for screening and contains several of the antigens associated with streptococcal products. Because some patients produce an antibody response to a limited number of streptococcal products, no single test is sufficiently sensitive to rule out infection. Clinical sensitivity is increased by performing additional tests when initial results are negative. The streptozyme test generally shows more false positives and false negatives than ASO and anti-DNase. A positive test for antihyaluronidase occurs in a smaller number of patients with recent streptococcal infections than ASO and anti-DNase

Interpret the following ASO results: Tube Nos. 1-4 (Todd unit 125): no hemolysis; Tube No. 5 (Todd unit 166): hemolysis A. Positive Todd unit 125 B. Positive Todd unit 166 C. No antistreptolysin O present D. Impossible to interpret

A An ASO titer is expressed in Todd units as the last tube that neutralizes (no visible hemolysis) the streptolysin O (SLO). Most laboratories consider an ASO titer significant if it is 166 Todd units or higher. However, people with a recent history of streptococcal infection may demonstrate an ASO titer of 166 or higher; demonstration of a rise in titer from acute to convalescent serum is required to confirm a current streptococcal infection. ASO is commonly measured using a rapid latex agglutination assay. These tests show agglutination when the ASO concentration is 200 IU/mL or higher

Which hepatitis B markers should be performed on blood products? A. HBsAg and anti-HBc B. Anti-HBs and anti-HBc C. HBeAg and HBcAg D. Anti-HBs and HBeAg

A Blood products are tested for HBsAg, an early indicator of infection, and anti-HBc, a marker that may persist for life. Following recovery from HBV infection, some patients demonstrate negative serology for HBsAg and anti-HBs but are positive for anti-HBc. Such patients are considered infective.

Which of the following methods used for HIV identification is considered a signal amplification technique? A. Branched chain DNA analysis B. DNA PCR C. Reverse transcriptase PCR D. Nucleic acid sequence based assay (NASBA)

A Branched chain DNA is a signal amplification technique, i.e., if you start with one copy of the gene you finish with one copy. The detection reagent is amplified, increasing the sensitivity of the assay.

Which tests are considered screening tests for HIV? A. ELISA, 4th generation, and rapid antibody tests B. Immunofluorescence, Western blot, radioimmuno-precipitation assay C. Culture, antigen capture assay, DNA amplification D. Reverse transcriptase and messenger RNA (mRNA) assay

A ELISA, rapid antibody tests, as well as the 4th generation automated antigen/antibody combination assays are screening tests for HIV. The 4th generation assays detect both antigen and antibody.

All of the following hepatitis viruses are spread through blood or blood products except: A. Hepatitis A B. Hepatitis B C. Hepatitis C D. Hepatitis D

A Hepatitis A is spread through the fecal-oral route and is the cause of infectious hepatitis. Hepatitis A virus has a shorter incubation period (2-7 weeks) than hepatitis B virus (1-6 months). Epidemics of hepatitis A virus can occur, especially when food and water become contaminated with raw sewage. Hepatitis E virus is also spread via the oral-fecal route and, like hepatitis A virus, has a short incubation period.

Which hepatitis B marker is the best indicator of early acute infection? A. HBsAg B. HBeAg C. Anti-HBc D. Anti-HBs

A Hepatitis B surface antigen (HBsAg) is the first marker to appear in hepatitis B virus infection. It is usually detected within 4 weeks of exposure (prior to the rise in transaminases) and persists for about 3 months after serum enzyme levels return to normal.

Why is laboratory diagnosis difficult in cases of Lyme disease? A. Clinical response may not be apparent upon initial infection; IgM antibody may not be detected until 3-6 weeks after the infection B. Laboratory tests may be designed to detect whole Borrelia burgdorferi, not flagellar antigen found early in infection C. Most laboratory tests are technically demanding and lack specificity D. Antibodies formed initially to B. burgdorferi may cross react in antigen tests for autoimmune diseases

A Lyme disease is caused by B. burgdorferi, a spirochete, and typical clinical symptoms such as rash or erythema chronicum migrans may be lacking in some infected individuals. Additionally, IgM antibody is not detectable by laboratory tests until 3-6 weeks after a tick bite, and IgG antibody develops later.

A newborn is to be tested for a vertically transmitted HIV infection. Which of the following tests is most useful? A. HIV PCR B. CD4 count C. Rapid HIV antibody test D. HIV IgM antibody test

A Neonatal HIV diagnosis is performed by screening for the presence of the virus. The current antibody tests are either IgG-specific or an IgG/IgM combination assay. Thus an infant whose mother is HIV positive will also be positive in the HIV antibody assay. Although the CD4 count may be a useful assay to determine disease activity, there are many causes of reduced CD4 numbers and this assay should not be used to diagnose HIV infection

Which statement concerning non-Forssman heterophile antibody is true? A. It is not absorbed by guinea pig antigen B. It is absorbed by guinea pig antigen C. It does not agglutinate horse RBCs D. It does not agglutinate sheep RBCs

A Non-Forssman antibody is not absorbed by guinea pig antigen. This is one of the principles of the Davidsohn differential test for antibodies to IM. These antibodies are non-Forssman; they are absorbed by sheep, horse, or beef RBCs but not by guinea pig kidney. Therefore, a heterophile titer remaining higher after absorption with guinea pig kidney than with beef RBCs indicates IM.

Which test is most likely to be positive in the tertiary stage of syphilis? A. FTA-ABS B. RPR C. VDRL D. Reagin screen test (RST)

A The FTA-ABS or one of the treponemal tests is more likely to be positive than a nontreponemal test in the tertiary stage of syphilis. In some cases, systemic lesions have subsided by the tertiary stage and the nontreponemal tests become seronegative. Although the FTA-ABS is the most sensitive test for tertiary syphilis, it will be positive in both treated and untreated cases

What criteria constitute the classification system for HIV infection? A. CD4-positive T-cell count and clinical symptoms B. Clinical symptoms, condition, duration, and number of positive bands on Western blot C. Presence or absence of lymphadenopathy D. Positive bands on Western blot and CD8-positive T-cell count

A The classification system for HIV infection is based upon a combination of CD4-positive T-cell count (helper T cells) and various categories of clinical symptoms. Classification is important in determining treatment options and the progression of the disease.

Interpret the following quantitative RPR test results. RPR titer: weakly reactive 1:8; reactive 1:8-1:64 A. Excess antibody, prozone effect B. Excess antigen, postzone effect C. Equivalence of antigen and antibody D. Impossible to interpret; testing error

A This patient may be in the secondary stage of syphilis and is producing large amounts of antibody to T. pallidum sufficient to cause antibody excess in the test. The test became strongly reactive only after the antibody was diluted.

How can interfering cold agglutinins be removed from a test sample? A. Centrifuge the serum and remove the top layer B. Incubate the clot at 1°C-4°C for several hours, then remove serum C. Incubate the serum at 56°C in a water bath for 30 minutes D. Use an anticoagulated sample

B Cold agglutinins will attach to autologous red cells if incubated at 1°C-4°C. The absorbed serum will be free of cold agglutinins.

Which serum antibody response usually characterizes the primary (early) stage of syphilis? A. Antibodies against syphilis are undetectable B. Detected 1-3 weeks after appearance of the primary chancre C. Detected in 50% of cases before the primary chancre disappears D. Detected within 2 weeks after infection

B During the primary stage of syphilis, about 90% of patients develop antibodies between 1 and 3 weeks after the appearance of the primary chancre.

Which of the following positive antibody tests may be an indication of recent vaccination or early primary infection for rubella in a patient with no clinical symptoms? A. Only IgG antibodies positive B. Only IgM antibodies positive C. Both IgG and IgM antibodies positive D. Fourfold rise in titer for IgG antibodies

B If only IgM antibodies are positive, this result indicates a recent vaccination or an early primary infection.

Serological tests for which disease may give a false-positive result if the patient has Lyme disease? A. AIDS B. Syphilis C. Cold agglutinins D. Hepatitis C

B Lyme disease is caused by a spirochete and may give positive results with some specific treponemal antibody tests for syphilis.

Which of the following fungal organisms is best diagnosed by an antibody detection test as opposed to an antibody detection assay? A. Histoplasma B. Cryptococcus C. Candida D. Aspergillus

B The Cryptococcus antibody response is not a reliable indicator of a current infection; thus, an antigen assay is normally used to monitor the disease. The antigen assay may be used for serum or spinal fluid and will decline in response to treatment much faster than a traditional antibody test. A urinary antigen test is available for histoplasmosis, and a serum galactomannan assay is available for Aspergillus. Those two assays preform better than antibody detection. No antigen test is available for Candida, thus antibody is the best serologic procedure for this organism.

What is the endpoint for the antistreptolysin O (ASO) latex agglutination assay? A. Highest serum dilution that shows no agglutination B. Highest serum dilution that shows agglutination C. Lowest serum dilution that shows agglutination D. Lowest serum dilution that shows no agglutination

B The latex test for ASO includes latex particles coated with streptolysin O. Serial dilutions are prepared and the highest dilution showing agglutination is the endpoint.

Which control shows the correct result for a valid ASO test? A. SLO control, no hemolysis B. Red cell control, no hemolysis C. Positive control, hemolysis in all tubes D. Hemolysis in both SLO and red cell control

B The red cell control contains no SLO and should show no hemolysis. The SLO control contains no serum and should show complete hemolysis. An ASO titer cannot be determined unless both the RBC and SLO controls demonstrate the expected results

Interpret the following results for HIV infection. ELISA: positive; repeat ELISA: negative; Western blot: no bands A. Positive for HIV B. Negative for HIV C. Indeterminate D. Further testing needed

B These results are not indicative of an HIV infection and may be due to a testing error in the first ELISA assay. Known false-positive ELISA reactions occur in autoimmune diseases, syphilis, alcoholism, and lymphoproliferative diseases. A sample is considered positive for HIV if it is repeatedly positive by ELISA or other screening method and positive by a confirmatory method.

An immunosuppressed patient has an unexplained anemia. The physician suspects a parvovirus B19 infection. A parvovirus IgM test is negative. The next course of action is to tell the physician: A. The patient does not have parvovirus B. A convalescent specimen is recommended in 4 weeks to determine if a fourfold rise in titer has occurred C. A parvovirus PCR is recommended D. That a recent transfusion for the patient's anemia may have resulted in a false-negative assay and the patient should be retested in 4 weeks

C A negative IgM assay rarely rules out an infection. While a convalescent specimen may be useful in many cases, in an immunosuppressed patient the convalescent specimen may remain negative in the presence of an infection. Thus a parvovirus PCR test is the preferred choice in this case. A false-negative result could conceivably be caused by multiple whole blood or plasma transfusions, but retesting for antibody a month later would not be beneficial to the patient.

Interpret the following results for EBV infection: IgG and IgM antibodies to viral capsid antigen (VCA) are positive. A. Infection in the past B. Infection with a mutual enhancer virus such as HIV C. Current infection D. Impossible to interpret; need more information

C Antibodies to both IgG and IgM VCA are found in a current infection with EBV. The IgG antibody may persist for life, but the IgM anti-VCA disappears within 4 months after the infection resolves.

What is the advantage of 4th-generation rapid HIV tests over earlier rapid HIV tests? A. They use recombinant antigens B. They detect multiple strains of HIV C. They detect p24 antigen D. They are quantitative

C Both 3rd-generation and 4th-generation rapid tests for HIV use recombinant and synthetic HIV antigens conjugated to a solid phase. The multivalent nature of these tests allows for detection of less common subgroups of HIV-1 and simultaneous detection of both HIV-1 and HIV-2. However, the 4th-generation assays also use solid-phase antibodies to p24 antigen to detect its presence. Because p24 antigen appears before antibodies to HIV, 4th-generation tests can detect infection 4-7 days earlier than tests based on antibody detection alone.

Blood products are tested for which virus before being transfused to newborns? A. EBV B. Human T-lymphotropic virus II (HTLV-II) C. Cytomegalovirus (CMV) D. Hepatitis D virus

C CMV can be life threatening if transmitted to a newborn through a blood product. HTLV-II is a rare virus, which like HIV, is a T-cell tropic RNA retrovirus. The virus has been associated with hairy cell leukemia, but this is not a consistent finding.

What type of antigen is used in the RPR card test? A. Live treponemal organisms B. Killed suspension of treponemal organisms C. Cardiolipin D. Tanned sheep cells

C Cardiolipin is extracted from animal tissues, such as beef hearts, and attached to carbon particles. In the presence of reagin, the particles will agglutinate.

All positive cold agglutinin tubes remain positive after 37°C incubation except the positive control. What is the most likely explanation for this situation? A. High titer cold agglutinins B. Contamination of the test system C. Antibody other than cold agglutinins D. Faulty water bath

C Cold agglutinins do not remain reactive above 30°C, and agglutination must disperse following incubation at 37°C. The most likely explanation when agglutination remains after 37°C incubation is that a warm alloantibody or autoantibody is present.

Which method is used to test for HIV infection in infants who are born to HIV-positive mothers? A. ELISA B. Western blot test C. Polymerase chain reaction D. Viral culture

C ELISA and Western blot primarily reflect the presence of maternal antibody. The PCR uses small amounts of blood and does not rely on the antibody response. PCR amplifies small amounts of viral nucleic acid and can detect less than 200 copies of viral RNA per milliliter of plasma. These qualities make PCR ideal for the testing of infants. Nucleic acid methods for HIV RNA include the Roche Amplicor reversetranscriptase assay, the branched DNA (bDNA) signal amplification method, and the nucleic acid sequence-based amplification (NASBA) method.

Which of the following statements regarding infection with hepatitis D virus is true? A. Occurs in patients with HIV infection B. Does not progress to chronic hepatitis C. Occurs in patients with hepatitis B D. Is not spread through blood or sexual contact

C Hepatitis D virus is an RNA virus that requires the surface antigen or envelope of the hepatitis B virus for entry into the hepatocyte. Consequently, hepatitis D virus can infect only patients who are coinfected with hepatitis B.

Which specimen is the sample of choice to evaluate latent or tertiary syphilis? A. Serum sample B. Chancre fluid C. CSF D. Joint fluid

C Latent syphilis usually begins after the second year of untreated infection. In some cases, the serological tests become negative. However, if neurosyphilis is present, cerebrospinal fluid serology will be positive and the CSF will display increased protein and pleocytosis characteristic of central nervous system infection.

A woman who has had five pregnancies subsequently tests positive for HIV by Western blot. What is the most likely reason for this result? A. Possible cross-reaction with herpes or EBV antibodies B. Interference from medication C. Cross-reaction with HLA antigens in the antigen preparation D. Possible technical error

C Multiparous women often have HLA antibodies. The Western blot antigens are derived from HIV grown in human cell lines having HLA antigens. A cross reaction with HLA antigen(s) in the Western blot could have occurred.

In monitoring an HIV-infected patient, which parameter may be expected to be the most sensitive indicator of the effectiveness of antiretroviral treatment? A. HIV antibody titer B. CD4:CD8 ratio C. HIV viral load D. Absolute total T-cell count

C The HIV viral load will rise or fall in response to treatment more quickly than any of the other listed parameters. The absolute CD4 count is also an indicator of treatment effectiveness and is used in resource-poor areas that might not have facilities for molecular testing available. Note that the absolute CD4 count is not one of the choices, however

What is the most likely explanation when a patient has clinical signs of viral hepatitis but tests negative for hepatitis A IgM, hepatitis B surface antigen, and hepatitis C Ab? A. Tests were performed improperly B. The patient does not have hepatitis C. The patient may be in the "core window" D. Clinical evaluation was performed improperly

C The patient may be in the "core window," the period of hepatitis B infection when both the surface antigen and surface antibody are undetectable. The IgM anti-hepatitis B core and the anti-hepatitis B core total antibody assays would be the only detectable markers in the serum of a patient in the core window phase of hepatitis B infection

What is the main difficulty associated with the development of an HIV vaccine? A. The virus has been difficult to culture; antigen extraction and concentration are extremely laborious B. Human trials cannot be performed C. Different strains of the virus are genetically diverse D. Anti-idiotype antibodies cannot be developed

C Vaccine development has been difficult primarily because of the genetic diversity among different strains of the virus, and new strains are constantly emerging. HIV-1 can be divided into two main subtypes designated M (for main) and O (for outlier). The M group is further divided into 9 subgroups, designated A-J (there is no E subgroup), based upon differences in the nucleotide sequence of the gag gene. Two remaining subtypes are designed N (non M and non O) and P (a subtype related to SIVgor). A vaccine has yet to be developed that is effective for all of the subgroups of HIV-1.

Which CD4:CD8 ratio is most likely in a patient with acquired immunodeficiency syndrome (AIDS)? A. 2:1 B. 3:1 C. 2:3 D. 1:2

D An inverted CD4:CD8 ratio (less than 1.0) is a common finding in an AIDS patient. The Centers for Disease Control and Prevention requires a CD4-positive (helper T) cell count of less than 200/μL or 14% in the absence of an AIDS-defining illness (e.g., Pneumocystis carinii pneumonia) in the case surveillance definition of AIDS.

Which hepatitis antibody confers immunity against reinfection with hepatitis B virus? A. Anti-HBc IgM B. Anti-HBc IgG C. Anti-HBe D. Anti-HBs

D Anti-HBs appears later in infection than anti-HBc and is used as a marker for immunity following infection or vaccination rather than for diagnosis of current infection.

A renal transplant recipient is found to have a rising creatinine level and reduced urine output. The physician orders a "Urine PCR" assay. When you call to find out what organism the physician wants to identify, you are told: A. Hepatitis C virus B. Legionella pneumophila C. EBV D. BK virus

D BK virus is a polyoma virus that can cause renal and urinary tract infections. The virus is an opportunistic pathogen and has become a well-recognized cause of poor renal function in kidney transplant recipients. Antibody testing is not practical or useful for this infection. The principal diagnostic assays are urinary cytology, and specific BK virus PCR testing in urine and serum. Although Legionella pneumophila can be diagnosed through a urinary antigen assay, that organism is not a primary cause of renal insufficiency in transplant patients.

Your cytology laboratory refers a Papanicolaou smear specimen to you for an assay designed to detect the presence of a virus associated with cervical cancer. You perform: A. An ELISA assay for anti-HSV-2 antibodies B. A molecular assay for HSV-2 C. An ELISA assay for HPV antibodies D. A molecular assay for HPV

D Cervical cell atypia and cervical cancer are associated with specific high-risk serotypes of human papilloma virus (HPV) infections. Although HPV antibody assays are available, they are not serotype specific, nor do they relate to disease activity. Thus molecular probe assays are the tests of choice to detect high-risk HPV infection. Although HSV-2 is associated with genital herpesvirus, that virus has not been shown to cause cervical cancer.

Which of the following is the most sensitive test to detect congenital syphilis? A. VDRL B. RPR C. Microhemagglutinin test for T. pallidum (MHA-TP) D. Polymerase chain reaction (PCR)

D The PCR will amplify a very small amount of DNA from T. pallidum and allow for detection of the organism in the infant. Antibody tests such as VDRL and RPR may detect maternal antibody only, not indicating if the infant has been infected.

A 12-year old girl has symptoms of fatigue and a localized lymphadenopathy. Laboratory tests reveal a peripheral blood lymphocytosis, a positive RPR, and a positive spot test for IM. What test should be performed next? A. HIV test by ELISA B. VDRL C. Epstein-Barr virus (EBV) specific antigen test D. Treponema pallidum particle agglutination (TP-PA) test

D The patient's symptoms are nonspecific and could be attributed to many potential causes. However, the patient's age, lymphocytosis, and serological results point to infectious mononucleosis (IM). The rapid spot test for antibodies seen in IM is highly specific. The EBV-specific antigen test is more sensitive but is unnecessary when the spot test is positive. HIV infection is uncommon at this age and is often associated with generalized lymphadenopathy and a normal or reduced total lymphocyte count. IM antibodies are commonly implicated as a cause of biological false-positive nontreponemal tests for syphilis. Therefore, a treponemal test for syphilis should be performed to document this phenomenon in this case

Which is most likely a positive Western blot result for infection with HIV? A. Band at p24 B. Band at gp60 C. Bands at p24 and p31 D. Bands at p24 and gp120

D To be considered positive by Western blot testing, bands must be found for at least two of the following three HIV proteins: gp41, p24, and gp120 or 160. The p24 band denotes antibody to a gag protein. The gp160 is the precursor protein from which gp120 and gp41 are made; these are env proteins

What constitutes a diagnosis of viral hepatitis? A. Abnormal test results for liver enzymes B. Clinical signs and symptoms C. Positive results for hepatitis markers D. All of these options

D To diagnose a case of hepatitis, the physician must consider clinical signs as well as laboratory tests that measure liver enzymes and hepatitis markers.

Interpret the following results for HIV infection. HIV 1,2 ELISA: positive; HIV-1 Western blot: indeterminate; HIV-1 p24 antigen: negative A. Positive for antibodies to human immunodeficiency virus, HIV-1 B. Positive for antibodies to human immunodeficiency virus, HIV-2 C. Cross reaction; biological false-positive result D. Additional testing required

D. Additional testing required D The indeterminate Western blot and negative p24 antigen assay indicate that HIV-1 infection is unlikely, However, additional testing is required to determine if the patient has antibodies to HIV-2 or if this could be a false-positive ELISA assay.