Laboratory Science Immunology and Serology 1 — Questions and Answers
Question 1: What does the ANA (antinuclear antibody) test detect, and what condition is it associated with?
- Antibodies against bacteria; associated with sepsis
- Autoantibodies against nuclear components; associated with systemic lupus erythematosus (SLE) (Correct answer)
- Antibodies against RBCs; associated with hemolytic anemia
- Antibodies against thyroid; associated with Hashimoto's disease
Correct answer: Autoantibodies against nuclear components; associated with systemic lupus erythematosus (SLE)
ANA detects autoantibodies targeting nuclear antigens (DNA, histones, ribonucleoproteins); a positive ANA with high titer is the hallmark screening test for SLE and other connective tissue diseases.
Question 2: Which immunoglobulin is the first antibody produced during primary immune response?
- IgG
- IgA
- IgM (Correct answer)
- IgE
Correct answer: IgM
IgM is the first immunoglobulin produced during primary immune response and is the largest antibody (pentamer); it's detected in acute infections and gradually replaced by IgG in secondary responses.
Question 3: What is the rheumatoid factor (RF) test measuring?
- Anti-CCP antibodies against citrullinated proteins
- IgM autoantibodies directed against the Fc region of IgG (Correct answer)
- Complement levels in blood
- HLA-B27 antigen on lymphocytes
Correct answer: IgM autoantibodies directed against the Fc region of IgG
Rheumatoid factor is typically IgM autoantibodies against the Fc region of IgG; elevated RF supports rheumatoid arthritis diagnosis but is not specific (also elevated in infections and other autoimmune diseases).
Question 4: A reactive RPR (Rapid Plasma Reagin) test should be confirmed with which more specific test for syphilis?
- VDRL test
- FTA-ABS (fluorescent treponemal antibody absorption) test (Correct answer)
- Darkfield microscopy only
- KOH preparation
Correct answer: FTA-ABS (fluorescent treponemal antibody absorption) test
RPR is a non-treponemal screening test prone to biological false positives; confirmation requires a treponemal-specific test like FTA-ABS or TP-PA that detects antibodies to T. pallidum antigens.
Question 5: Which blood group antigen system is most clinically important for transfusion compatibility?
- Lewis system
- Kell system
- ABO and Rh (D antigen) systems (Correct answer)
- Duffy system
Correct answer: ABO and Rh (D antigen) systems
ABO incompatibility causes immediate intravascular hemolytic transfusion reactions (potentially fatal), while Rh(D) incompatibility causes hemolytic disease of the fetus/newborn and delayed hemolytic reactions.
Question 6: What is a direct antiglobulin test (DAT) used to detect?
- Free antibodies in patient serum
- Antibodies or complement bound directly to the patient's red blood cells (Correct answer)
- Bacterial antigens in blood
- Platelet antibodies
Correct answer: Antibodies or complement bound directly to the patient's red blood cells
The DAT (direct Coombs test) detects IgG or complement proteins already coating the patient's RBCs in vivo, used to diagnose autoimmune hemolytic anemia and hemolytic disease of the newborn.
Laboratory Science Immunology and Serology 1
What does the ANA (antinuclear antibody) test detect, and what condition is it associated with?