Medical Technologist Test Medical Technologist Knowledge 5 — Questions and Answers
Question 1: Which test is used to differentiate Streptococcus pyogenes (Group A) from other beta-hemolytic streptococci?
- Optochin susceptibility
- Bacitracin susceptibility (Correct answer)
- CAMP test
- Coagulase test
Correct answer: Bacitracin susceptibility
Group A streptococci (S. pyogenes) are susceptible to bacitracin, differentiating them from other beta-hemolytic streptococcal groups.
Question 2: A patient's red blood cells fail to agglutinate with anti-A, anti-B, and anti-D, but the serum has no alloantibodies. This pattern is consistent with:
- Group O, Rh-negative
- Bombay phenotype (Oh) (Correct answer)
- Group AB, Rh-negative
- Weak D (Du) variant
Correct answer: Bombay phenotype (Oh)
Bombay phenotype lacks H antigen, so cells type as O but also lack normal H antigen, and serum contains anti-H that reacts with all common donor cells.
Question 3: The principle behind the ELISA (enzyme-linked immunosorbent assay) technique is:
- Precipitation of antigen-antibody complexes in gel
- Fluorescent labeling of antibodies detected by UV microscopy
- Enzyme-labeled antibody binding detected by color change upon substrate addition (Correct answer)
- Agglutination of latex particles coated with antigen
Correct answer: Enzyme-labeled antibody binding detected by color change upon substrate addition
ELISA uses an enzyme-conjugated antibody; addition of substrate causes a colorimetric reaction proportional to the amount of antigen or antibody present.
Question 4: Which finding on a peripheral smear is characteristic of iron deficiency anemia?
- Macrocytosis with hypersegmented neutrophils
- Microcytosis with hypochromia and target cells (Correct answer)
- Spherocytes and increased MCHC
- Sickle cells and Howell-Jolly bodies
Correct answer: Microcytosis with hypochromia and target cells
Iron deficiency anemia produces microcytic, hypochromic red cells, often with target cells due to excess membrane relative to hemoglobin content.
Question 5: The confirmatory test for HIV infection after a reactive screening immunoassay is:
- Repeat ELISA
- HIV-1/HIV-2 antibody differentiation immunoassay or HIV RNA NAT (Correct answer)
- CD4 count
- Western blot (no longer preferred per 2014 CDC algorithm)
Correct answer: HIV-1/HIV-2 antibody differentiation immunoassay or HIV RNA NAT
Per the current CDC 2014 algorithm, a reactive 4th-generation immunoassay is confirmed with an HIV-1/HIV-2 antibody differentiation assay, followed by HIV-1 RNA NAT if results are discordant.
Question 6: Which coagulation factor is measured by the prothrombin time (PT) but NOT the aPTT?
- Factor VIII
- Factor IX
- Factor VII (Correct answer)
- Factor X
Correct answer: Factor VII
Factor VII is part of the extrinsic pathway and is measured by PT (via tissue factor), while aPTT evaluates the intrinsic pathway (Factors VIII, IX, XI, XII).
Question 7: A urine culture growing >100,000 CFU/mL of a single organism from a clean-catch midstream specimen is interpreted as:
- Contamination
- Colonization only
- Significant bacteriuria indicating urinary tract infection (Correct answer)
- Normal flora
Correct answer: Significant bacteriuria indicating urinary tract infection
≥100,000 CFU/mL (10^5) of a single uropathogen from a properly collected midstream specimen is the classic threshold for significant bacteriuria.
Medical Technologist Test Medical Technologist Knowledge 5
Which test is used to differentiate Streptococcus pyogenes (Group A) from other beta-hemolytic streptococci?