MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 41
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
Complement receptor 1 (CR1, CD35) on human red cells mainly helps to:
C3b-coated immune complexes bind CR1 on red cells and are stripped off by macrophages in the liver and spleen. CR1 also acts as a cofactor for factor I.
Plain Haemophilus influenzae type b polysaccharide vaccine works poorly in infants, but the conjugate vaccine works well because protein conjugation:
Polysaccharides are T-independent antigens that young infants respond to poorly. Linking them to a protein carrier lets helper T cells help polysaccharide-specific B cells, producing IgG and memory.
A healthcare worker completed hepatitis B vaccination and has never been infected. Which serological profile is expected?
The recombinant vaccine contains only HBsAg, so it produces anti-HBs alone. Anti-HBc appears only after natural infection.
In Ouchterlony double diffusion, the precipitin lines from two neighbouring antigen wells join, but one line extends past the junction as a spur. This indicates:
A spur means one antigen has all the epitopes of the other plus extra ones, so antibodies to the extra epitopes pass the junction: partial identity. Complete identity gives a smooth fused arc without a spur.
A TSH result by two-site sandwich immunoassay is unexpectedly high and falls to normal after the sample is treated with a heterophile blocking reagent. The interference was most likely due to:
Heterophile or human anti-mouse antibodies can link the capture and labelled antibodies without analyte, causing false-high sandwich results that correct with blocking reagents. Biotin causes falsely low sandwich results.
Latex particles coated with antibody are used to detect bacterial antigen in a sample. This technique is:
In reverse passive agglutination, carrier particles carry antibody and detect soluble antigen. Passive agglutination uses antigen-coated carriers to detect patient antibody.
Coagglutination tests use Staphylococcus aureus cells as carriers because of their:
Protein A binds IgG by its Fc portion, leaving Fab sites facing outward to agglutinate with antigen. Clumping factor binds fibrinogen, not antibody.
A blood donor has a reactive anti-HCV immunoassay, but HCV RNA is not detected. The most likely interpretation is:
Antibody without detectable RNA suggests cleared past infection or a false-positive screen; a second antibody assay can separate these. Window-period infection would show RNA without antibody.
A 4-month-old boy has severe infections and very low T and NK cells with normal B-cell numbers. The most likely defect is in the:
X-linked SCID from IL2RG mutation (T−B+NK−) blocks IL-7 and IL-15 signalling needed for T and NK development. Bruton tyrosine kinase defects cause absent B cells with normal T cells.
A 28-year-old has recurrent sinus and lung infections. IgG and IgA are low, B-cell numbers are normal and antibody response to vaccines is poor. The most likely diagnosis is:
CVID usually presents after childhood with low IgG plus low IgA or IgM, poor vaccine responses and normal or slightly low B-cell numbers. X-linked agammaglobulinaemia presents in infancy with absent B cells.
A child has eczema, recurrent 'cold' staphylococcal skin abscesses, pneumonias with lung cysts and serum IgE above 2000 IU/mL. The most likely diagnosis is:
Autosomal dominant hyper-IgE (Job) syndrome from STAT3 mutation gives very high IgE, eczema, cold abscesses and pneumatoceles. Wiskott-Aldrich syndrome also has eczema but with thrombocytopenia and small platelets.
A seronegative stem cell recipient needs transfusion. Which component attribute best reduces the risk of transfusion-transmitted cytomegalovirus?
CMV lives in donor leukocytes, so leukoreduction or use of CMV-seronegative donors reduces transmission. Irradiation prevents TA-GVHD but does not remove CMV.
In a Severinghaus pCO₂ electrode, carbon dioxide is measured by detecting:
CO₂ diffuses through the membrane into bicarbonate solution, forming carbonic acid and lowering pH, which a glass electrode senses (potentiometric). Current at a platinum cathode describes the Clark pO₂ electrode.
Isoelectric focusing separates proteins according to their:
In isoelectric focusing each protein migrates in a pH gradient until it reaches the pH where its net charge is zero (pI), then stops. SDS-PAGE, not IEF, separates mainly by size.
A solution has an absorbance of 0.50. What is its percent transmittance (%T)?
A = 2 − log %T, so log %T = 1.5 and %T = 10^1.5 ≈ 31.6%. Absorbance and %T are logarithmically, not linearly, related, so 50% is wrong.
Serum results: sodium 140 mmol/L, glucose 180 mg/dL, BUN 28 mg/dL. Using 2 × Na + glucose/18 + BUN/2.8, the calculated osmolality is:
2 × 140 = 280; 180 ÷ 18 = 10; 28 ÷ 2.8 = 10; total = 300 mOsm/kg. Omitting either glucose or BUN term gives 290.
A serial dilution is made in which each tube is a 1:3 dilution of the previous tube. Tube 1 is a 1:3 dilution of serum. What is the dilution in tube 4?
Serial dilutions multiply: 1:3 × 3 × 3 × 3 = 1:81 in tube 4. Adding (3 × 4 = 12) instead of multiplying is a common error; 1:27 is tube 3.
An automated WBC count is 12.0 × 10⁹/L. The differential shows 20 nucleated red blood cells per 100 WBCs. The corrected WBC count is:
Corrected WBC = observed WBC × 100 ÷ (100 + nRBC) = 12.0 × 100/120 = 10.0 × 10⁹/L. Subtracting 20% (9.6) is incorrect.
A patient has a reticulocyte count of 6.0% and a haematocrit of 20%. Using a normal haematocrit of 45%, the corrected reticulocyte count is:
Corrected retic = 6.0% × (20/45) = 2.67%, about 2.7%. Inverting the ratio (45/20) gives 13.5%.
Under the OSHA bloodborne pathogens standard, the hepatitis B vaccine for an at-risk laboratory employee must be:
Employers must offer HBV vaccination at no cost within 10 working days of initial assignment. Employees may decline but must sign a declination form.