MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 28
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
A man with blurred vision, headaches and nose bleeds has an IgM monoclonal protein and lymphoplasmacytic marrow infiltrate. Which mutation is found in over 90% of such cases?
Waldenström macroglobulinemia (lymphoplasmacytic lymphoma with IgM) carries MYD88 L265P in most cases; IgM causes hyperviscosity. BRAF V600E is typical of hairy cell leukemia.
Which condition can falsely raise the WBC count on an impedance cell counter?
NRBC nuclei survive lysis and are sized like lymphocytes, so they are counted as WBCs unless corrected. Bilirubin affects hemoglobin measurement rather than WBC count.
On most automated analyzers, the 'immature granulocyte' (IG) count includes:
The IG parameter counts promyelocytes, myelocytes and metamyelocytes. Bands are counted with neutrophils and blasts are flagged separately.
Where on a wedge smear should the differential count be performed?
The count is done in the monolayer where RBCs barely touch. Large cells collect at edges and the feathered end, and the thick area distorts morphology.
A patient on chemotherapy has WBC 2.0 × 10^9/L with 30% segmented neutrophils and 5% bands. The absolute neutrophil count and category are:
ANC = 2.0 × (0.30 + 0.05) = 0.70 × 10^9/L. Values 0.5–1.0 are moderate; below 0.5 is severe.
A patient with a positive ANA has high-titre anti-U1-RNP as the only specific autoantibody, Raynaud phenomenon and swollen hands. The most likely diagnosis is:
A high titre of anti-U1-RNP is a defining feature of mixed connective tissue disease. Drug-induced lupus is associated with anti-histone antibodies.
Anti-SS-A (Ro) antibodies in a pregnant woman carry a risk of which condition in the newborn?
Maternal IgG anti-Ro/SS-A crosses the placenta and can damage the fetal cardiac conduction system, causing congenital heart block and neonatal lupus rash.
A patient with myositis, interstitial lung disease and 'mechanic's hands' most likely has which antibody?
Anti-Jo-1 (histidyl-tRNA synthetase) defines the antisynthetase syndrome: myositis, interstitial lung disease, arthritis and mechanic's hands. Its ANA pattern is cytoplasmic.
The preferred initial serologic screening test for celiac disease in a patient with normal total IgA is:
IgA anti-tTG is sensitive and specific and is the recommended first test. Total IgA should be checked because IgA deficiency causes false-negative IgA-based tests.
Post-streptococcal glomerulonephritis with granular deposits and low C3 is an example of which hypersensitivity type?
Circulating immune complexes deposit in glomeruli and activate complement, giving a lumpy-bumpy granular pattern and low C3. This is type III (immune complex) hypersensitivity.
A patient develops fever, rash, arthralgia and proteinuria 8–10 days after receiving antivenom made in horses. The most likely mechanism is:
Serum sickness is a type III reaction: antibodies to foreign serum proteins form immune complexes about 1–2 weeks after exposure. Anaphylaxis would occur within minutes.
Natural killer (NK) cells are best identified by which marker combination?
NK cells lack CD3 (no T-cell receptor) but express CD16 and CD56. CD3+ CD56+ cells are NKT cells, a different T-cell subset.
Papain digestion of an IgG molecule produces:
Papain cuts above the hinge disulfide bonds, giving two monovalent Fab fragments and one crystallizable Fc fragment. Pepsin cuts below the hinge, giving one divalent F(ab')2.
A 25-year-old has recurrent attacks of non-itchy swelling of the face and bowel wall without urticaria. C4 is low between attacks. Which protein is most likely deficient?
Hereditary angioedema is caused by C1 inhibitor deficiency, leading to uncontrolled C1 activity (low C4) and excess bradykinin. Urticaria is typically absent.
Interferon-gamma's most important effect in cell-mediated immunity is to:
Interferon-gamma, produced by Th1 cells and NK cells, activates macrophages and increases MHC expression. This is key in defense against intracellular organisms such as mycobacteria.
Regulatory T cells that maintain self-tolerance are typically characterised by:
Regulatory T cells express CD4, high CD25 (IL-2 receptor alpha) and the transcription factor FOXP3. Loss of FOXP3 causes the severe autoimmune syndrome IPEX.
In Ouchterlony double diffusion, precipitin lines that cross each other completely indicate:
Crossing lines mean the two antigens share no epitopes (non-identity). Fused arcs indicate identity and a spur indicates partial identity.
A one-step sandwich immunoassay gives a falsely low result for an extremely high hCG level. The best troubleshooting step is to:
Very high antigen saturates both capture and detection antibodies (high-dose hook effect). Diluting the sample brings it into the measuring range and reveals the true high value.
In the reverse syphilis screening algorithm, the treponemal EIA is reactive but the RPR is non-reactive. The next step is to:
A discordant EIA+/RPR− result needs a second treponemal test. If TP-PA is reactive it suggests past treated or untreated syphilis; if non-reactive the EIA is likely false-positive.
In a complement-dependent cytotoxicity (CDC) crossmatch, the test uses:
Recipient serum is incubated with donor lymphocytes and complement. Cell death shows donor-specific cytotoxic antibody, a contraindication to transplant.