MLT GlobeMOH exam preparation (UAE) – page 24
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
Many IgG anti-Rh antibodies coat red cells in saline but fail to produce visible clumping. Such antibodies are termed:
IgG molecules are too small to span the distance between red cells in saline, so they sensitise without agglutinating; they are detected with antiglobulin or enhancement media.
In suspected acromegaly, which statement about laboratory diagnosis is correct?
Because GH is pulsatile, random values overlap with normal. Raised IGF-1 plus failure of GH to suppress after 75 g glucose confirms the diagnosis.
Besides yolk sac tumor, markedly raised serum AFP is characteristic of:
AFP is produced by fetal liver and yolk sac, and re-expressed by hepatocellular carcinoma. Choriocarcinoma secretes hCG, and prostatic carcinoma PSA.
A sustained platelet count above 450 × 10^9/L with large platelets, no reactive cause and a CALR mutation is most consistent with:
Essential thrombocythemia is an MPN with persistent thrombocytosis (at least 450 × 10^9/L) and a JAK2, CALR or MPL mutation in most patients. Reactive causes such as iron deficiency, infection or surgery must be excluded first.
Low albumin with a markedly increased alpha-2 band on electrophoresis suggests:
In nephrotic syndrome small proteins such as albumin are lost in urine, while the large alpha-2 macroglobulin is kept and the liver makes more of it, so the alpha-2 band stands out.
Measured serum osmolality is 320 mOsm/kg and calculated osmolality is 290 mOsm/kg. This osmolal gap most suggests:
The osmolal gap (measured minus calculated) is 30, well above the usual limit of about 10. It points to an osmotically active substance not in the formula, most often alcohols or ethylene glycol.
The preferred test to diagnose paroxysmal nocturnal hemoglobinuria (PNH) is:
PNH cells lack GPI-anchored proteins, including the complement regulators CD55 and CD59, so complement lyses them. Flow cytometry has replaced the older Ham and sucrose lysis tests.
A fourth-generation HIV screening immunoassay detects:
Adding p24 antigen detection shortens the window period compared with antibody-only tests, because p24 appears before antibodies. Reactive results go on to a differentiation assay and, if needed, RNA testing.
Waxy casts with cracked edges are associated with:
Waxy casts form as granular casts degenerate during long stasis in the tubules. Broad waxy casts suggest dilated tubules in end-stage kidney disease ('renal failure casts').
Many 'picket fence' (monohydrate) calcium oxalate crystals in a comatose patient with a high osmolal gap suggest poisoning with:
Ethylene glycol is metabolised to oxalic acid, which forms calcium oxalate crystals, often monohydrate, in urine. Methanol does not produce oxalate crystals.
A false-negative nitrite test in a patient with a UTI is most likely when:
Bacteria need about 4 hours in the bladder to convert nitrate to nitrite, and Enterococcus and yeasts do not. A first morning sample is best. Standing at room temperature can cause false positives.
Ten days after transfusion, a patient's hemoglobin falls, and the DAT is positive with anti-IgG. The eluate reacts only with Jk(a+) cells. This indicates:
An alloantibody bound to transfused antigen-positive cells after a secondary (anamnestic) response is typical of a delayed hemolytic reaction. Autoantibody eluates usually react with all cells.
A patient with warm AIHA has life-threatening anemia, and all crossmatches are incompatible. After alloantibodies are excluded by adsorption, what should be done?
Transfusion should not be withheld when life is at risk. Once alloantibodies are excluded, compatible-type units are given slowly with close monitoring, even if the crossmatch is incompatible.
At the end of storage, platelet units must have a pH of at least:
AABB requires pH ≥ 6.2 at the end of the allowed storage time. Low pH causes platelets to lose their disc shape and viability.
A healthy donor weighs 60 kg. What is the largest whole blood volume (including test samples) that may be collected?
The maximum collection is 10.5 mL/kg of body weight, including samples: 60 × 10.5 = 630 mL. 525 mL is the limit for a 50 kg donor.
Which medication leads to the LONGEST donor deferral because it is teratogenic and persists in the body?
Acitretin requires a 3-year deferral. Dutasteride needs 6 months, while finasteride and isotretinoin need about 1 month.
Which antigen commonly shows dosage, giving stronger reactions with homozygous cells?
Duffy, Kidd, MNS and most Rh antigens (not D) show dosage because homozygous cells carry more antigen. K, Lea and P1 do not typically show dosage.
Cw is best described as:
Cw is a low-prevalence Rh antigen. Anti-Cw may be missed by screening cells and appear as an incompatible crossmatch.
Why can Yersinia enterocolitica contaminate red cell units and cause septic reactions?
Yersinia is cold-tolerant and iron-loving, so it multiplies in refrigerated red cells and releases endotoxin. Most other bacteria grow better in platelets at room temperature.
A multiparous woman has a platelet count of 5 × 10^9/L with bleeding 8 days after a red cell transfusion. Which antibody is most likely responsible?
Post-transfusion purpura occurs 5–10 days after transfusion, mostly in HPA-1a-negative women sensitized by pregnancy. Their own platelets are destroyed too; IVIG is the treatment.