Medical Lab Science: Exam Q&A #3 + Answers

MEDICAL LABORATORY SCIENCE SUMMATIVE EXAM REVIEW QUESTIONS #03 + ANSWERS & RATIONALIZATIONS 1. What is the lowest level of hormone for which most current serum hCG tests can give a positive result? a. 25 mIU/mL b. 50 mIU/mL c. 100 mIU/mL d. 200 mIU/mL 2. In the card pregnancy test, if the test band appears very faint, it is recommended that it is: a. Reported as positive b. Reported as negative c. Test is considered invalid d. New sample collected 48 hours later and tested 3. Direct examination of the treponemes: a. Light microscopy b. Darkfield microscopy c. VDRL testing d. RPR testing 4. Which serum antibody response usually characterizes the primary (early) stage of syphilis? a. Antibodies against syphilis are undetectable b. Detected 1 to 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 5. 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 6. 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 7. Speed and time of rotation for serum VDRL test: a. 100 rpm for 4 minutes b. 100 rpm for 8 minutes c. 180 rpm for 4 minutes d. 180 rpm for 8 minutes 8. Speed and time of rotation for CSF VDRL test: a. 100 rpm for 4 minutes b. 100 rpm for 8 minutes c. 180 rpm for 4 minutes d. 180 rpm for 8 minutes 9. Speed and time of rotation for RPR: a. 100 rpm for 4 minutes b. 100 rpm for 8 minutes c. 180 rpm for 4 minutes d. 180 rpm for 8 minutes 10. In the RPR test, what is the gauge of the needle for antigen delivery? a. 16 b. 18 c. 20 d. 21 11. A widely used hemagglutination test for detecting antibody to Treponema pallidum is: a. MHA-TP test b. FTA-ABS test c. VDRL test d. TPI test 12. Which test is recommended for testing cerebrospinal fluid for detection of neurosyphilis? a. RPR b. VDRL c. FTA-ABS d. Enzyme immunoassay 13. Which specimen is the sample of choice to evaluate latent or tertiary syphilis? a. Serum sample b. Chancre fluid c. CSF d. Joint fluid 14. 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) 15. A biological false-positive reaction is least likely with which test for syphilis? a. VDRL b. FTA-ABS c. RPR d. All are equally likely to detect a false-positive result 16. Which of the following is the most sensitive test to detect congenital syphilis? a. VDRL b. RPR c. Microhemagglutination test for T. pallidum (MHA-TP) d. Polymerase chain reaction (PCR) 17. 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 18. 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 19. A single ASO titer is considered to be moderately elevated if the titer is at least ___ Todd units in an adult. a. 200 Todd units b. 240 Todd units c. 320 Todd units d. 340 Todd units 20. A single ASO titer is considered to be moderately elevated if the titer is at least ___ Todd units in a child. a. 200 Todd units b. 240 Todd units c. 320 Todd units d. 340 Todd units 1 21. 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 22. 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 23. Which of the following was a surrogate test for hepatitis that is no longer required? a. ALT b. Anti-HBc c. CMV d. HBsAg 24. The first serologic marker to appear in patients with acute hepatitis B virus infection is a. Anti-HBs b. Anti-HBc c. Anti-HBe d. HBsAg 25. Which hepatitis B marker is the best indicator of early acute infection? a. HBsAg b. HBeAg c. Anti-HBc d. Anti-HBs 26. Which surface marker is a reliable marker for the presence of high levels of hepatitis B virus (HBV) and a high degree of infectivity? a. HBe Ag b. HBs Ag c. HBc Ag d. Anti-HBsAg 27. Which is the first antibody detected in serum after infection with hepatitis B virus (HBV)? a. Anti-HBs b. Anti-HBc IgM → also found in window period c. Anti-HBe d. All are detectable at the same time 28. Which antibody persists in low-level carriers of hepatitis B virus? a. IgM anti-HBc b. IgG anti-HBc → lifelong marker of HBV infection c. IgM anti-HBe d. IgG anti-HBs 29. What assay would confirm the immune status of the hepatitis B virus? a. HBsAg b. Anti-HBs → past infection + immunization c. IgM anti-HBcAg d. Hepatitis C Ag 30. A hospital employee received the final dose of the hepatitis B vaccine 3 weeks ago. She wants to donate blood. Which of the following results are expected from the hepatitis screen, and will she be allowed to donate blood? a. HBsAg, positive; anti-HBc, negative; she may donate b. HBsAg, negative; anti-HBc, positive; she may not donate c. HBsAg, positive; anti-HBc, positive; she may not donate d. HBsAg, negative; anti-HBc, negative; she may donate 31. 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 → (-) anti-HBs 32. 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 33. 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 34. 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 35. Antibodies to which of the following viral antigens are usually the first to be detected in HIV infection? a. gp120 b. gp160 c. gp41 d. p24 36. Which of the following combinations of bands would represent a positive Western blot for HIV antibody? a. p24 and p55 b. p24 and p31 c. gp41 and gp120 d. p31 and p55 → Result should be reported as positive if at least two of the following three bands are present: p24, gp41, and gp120/gp160. → The Western blot, which was used for many years to confirm positive HIV antibody screening test results, detects antibody specificities to individual HIV antigens. It is no longer recommended for diagnosis of HIV because it is labor intensive, relatively insensitive, and has a long result turnaround time. 2 37. Interpret the following results for HIV infection. • ELISA: positive • Repeat ELISA: negative • Western blot: no bands 38. 39. 40. 41. 42. 43. a. Positive for HIV b. Negative for HIV c. Indeterminate d. Further testing needed 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 Which of the following tests is currently recommended by the CDC to confirm a positive screening test result for HIV infection? a. Rapid test for HIV-1 and HIV-2 antibodies b. Western blot c. Molecular testing for HIV RNA d. HIV viral culture 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 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 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 HTLV-I and HTLV-II can be transmitted by: a. Bloodborne (transfusion, IV drug abuse) b. Sexual contact (commonly from men to women) c. Mother-to-child (mainly through breastfeeding) d. All of these → These viruses have RNA as their nucleic acid and the enzyme, reverse transcriptase, whose function is to transcribe the viral RNA into DNA. → HTLV-I transforms CD4+ T lymphocytes into malignant cells in a small percentage of individuals through mechanisms mediated by the tax protein, which result in increased cell proliferation and accumulation of harmful genetic mutations. → The tests most commonly used for screening are ELISA or CLIA methods that incorporate recombinant antigens or synthetic peptides from both HTLV-I and HTLV-II. Commercially available Western blot assays are most commonly used for confirmation; line immunoassays (LIA) andIFA tests have also been developed. 44. Individuals exposed to EBV maintain an asymptomatic latent infection in: a. B cells b. T cells c. All lymphocytes d. Monocytes 45. 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 → EBV infection antibodies ▪ Primary infection: ab to VCA ▪ Reactivation: ab to EA & EBNA ▪ Infection in the past: ab to VCA & EBNA 46. Two cross-reacting antigen types of herpes simplex virus have been identified: a. EBV and CMV b. HHV6 and HHV7 c. VZV and CMV d. HSV1 and HSV2 47. Cross-reactions in the complement fixation test for Histoplasma capsulatum occur in patients with _____; but titers appear to be lower. a. Aspergillosis b. Blastomycosis c. Aspergillosis, blastomycosis d. Blastomycosis, aspergillosis, coccidiomycosis 48. Which of the following fungal organisms is best diagnosed by an antigen detection test as opposed to an antibody detection assay? a. Histoplasma b. Cryptococcus c. Candida d. Aspergillus 49. Latex agglutination for cryptococcal _____ is now recommended test for Cryptococcus neoformans. a. Polysaccharide capsule b. Antigen c. Antibody d. Nucleic acids 50. Serological testing provides the most practical and reliable means of confirming a measles diagnosis. Samples collected before ___ may yield false-negative results, and repeat testing on a later sample is recommended in that situation. a. 72 hours b. 5 days c. 6 days d. 9 days → IgM antibodies become detectable 3 to 4 days after appearance of symptoms and persist for 8 to 12 weeks. 3