MLT GlobeMOH exam preparation (UAE) – page 34
700 practice MCQs for the MOH medical laboratory exam. Level: Basic to intermediate.
A patient with an inherited giant-platelet disorder has an impedance platelet count much lower than the smear estimate. Which method gives a more reliable count?
Giant platelets exceed the impedance platelet size threshold and are missed or counted as red cells; fluorescent or immunologic (CD61) optical methods identify platelets by staining. Warming only helps cold-reacting interferences.
A patient with oculocutaneous albinism and bleeding has absent secondary wave aggregation and platelets lacking dense granules on electron microscopy. The diagnosis is:
Hermansky-Pudlak syndrome is a dense-granule (δ-storage pool) disorder with albinism. Without released ADP, the secondary wave is lost.
An infant has severe macrocytic anemia with very low reticulocytes, normal white cells and platelets, and raised red cell adenosine deaminase. The most likely diagnosis is:
Diamond-Blackfan anemia is a congenital pure red cell aplasia presenting in infancy, often macrocytic, with raised erythrocyte ADA. Transient erythroblastopenia occurs in older children, is normocytic and has normal ADA.
A kappa:lambda free light chain ratio in serum is used mainly to detect:
Each B-cell clone makes only one light chain type. A clonal plasma cell disorder produces excess of one type, giving an abnormal kappa:lambda ratio.
A patient with severe hypertriglyceridemia has sodium 126 mmol/L by indirect ISE but 140 mmol/L by direct ISE on a blood gas analyzer. The best explanation is:
Indirect ISE dilutes the sample and assumes normal plasma water; excess lipid lowers plasma water, giving falsely low sodium. Direct ISE measures activity in plasma water and is unaffected.
Blood cultures are collected into aerobic and anaerobic bottles using a butterfly (winged) set. Which bottle should be filled first and why?
The tubing contains air, which enters the first bottle filled. Filling the aerobic bottle first keeps oxygen out of the anaerobic bottle.
A coagulase-negative staphylococcus from blood of a patient with native-valve endocarditis is PYR positive and ornithine decarboxylase positive. The most likely species is:
S. lugdunensis is PYR and ornithine decarboxylase positive and behaves aggressively like S. aureus in endocarditis. S. epidermidis is PYR negative in most strains and less virulent.
A motile enterococcus identified as E. gallinarum has a vancomycin MIC of 8 µg/mL and is teicoplanin susceptible. This resistance is best explained by:
E. gallinarum and E. casseliflavus carry intrinsic vanC, giving low-level vancomycin resistance. They are motile, unlike E. faecalis and E. faecium, and have less infection-control significance.
A yeast from urine forms small cells only, with no pseudohyphae on cornmeal agar, and rapidly hydrolyses trehalose. The most likely identification is:
C. glabrata forms small blastoconidia without pseudohyphae and gives a rapid trehalose test. C. albicans and C. tropicalis form pseudohyphae; C. krusei forms elongated 'crossed-matchstick' pseudohyphae.
A yeast-like isolate from blood produces arthroconidia and blastoconidia on cornmeal agar and is urease positive. The most likely genus is:
Trichosporon produces both arthroconidia and blastoconidia and is urease positive. Geotrichum forms arthroconidia without blastoconidia and is urease negative.
Serum (1,3)-beta-D-glucan is positive in many invasive fungal infections but is characteristically LOW or negative in infection with:
Mucorales contain little beta-D-glucan and Cryptococcus is masked by its capsule, so the test is often negative. Pneumocystis, Candida and Aspergillus usually give positive results.
A Haemophilus isolate produces red fluorescence under UV light in the porphyrin (delta-aminolevulinic acid) test. This result means the isolate:
A positive porphyrin test shows the organism can make porphyrins and heme from ALA, so it does not need X factor (e.g. H. parainfluenzae). H. influenzae is porphyrin negative because it requires X factor.
Which CSF chemistry finding best helps separate bacterial from viral meningitis, especially after antibiotics are started?
CSF lactate rises markedly in bacterial meningitis due to anaerobic metabolism and neutrophils, and stays high for a time after antibiotics. It is usually normal or slightly raised in viral meningitis.
A group A patient received a group O hematopoietic stem cell transplant (minor ABO mismatch). Which red cells should be transfused after the transplant?
Donor-derived lymphocytes make anti-A that can hemolyse group A cells (passenger lymphocyte syndrome). Group O red cells are compatible with both recipient and donor.
A Kleihauer-Betke test shows 30 fetal cells in 2000 cells counted. Using 5000 mL maternal blood volume, how many 300 µg RhIG vials are needed?
30/2000 = 1.5%. Fetal bleed = 1.5 × 50 = 75 mL whole blood. 75 ÷ 30 = 2.5, rounded up to 3, then add 1 vial = 4 vials.
A patient with sickle cell disease is transfused. One week later, hemoglobin is lower than before transfusion and reticulocytes have fallen. What is the most likely diagnosis?
In hyperhemolysis, both donor and the patient's own red cells are destroyed, so hemoglobin falls below the pretransfusion level. More transfusion can worsen it; immunosuppression is used.
A patient has acute respiratory failure with pCO2 70 mmHg. Baseline HCO3− was 24 mmol/L. If the disorder is purely acute with expected compensation (1 mmol/L per 10 mmHg), HCO3− should be about:
pCO2 rose by 30 mmHg, so acute buffering raises HCO3− by about 3 mmol/L, giving 27 mmol/L. About 35 mmol/L would fit chronic compensation (3.5 per 10 mmHg).
A pregnant woman fails the 50 g screen. Her 100 g 3-hour OGTT: fasting 90, 1 h 185, 2 h 160, 3 h 130 mg/dL. Using Carpenter–Coustan limits (95/180/155/140 mg/dL), the result is:
In the two-step approach, gestational diabetes is diagnosed when at least two of the four values meet or exceed the limits. Here the 1-hour and 2-hour values are abnormal.
Which three serum markers are used in the "S" (serum marker) category of TNM staging for testicular germ cell tumors?
AFP, hCG and LDH levels after orchiectomy define the S category and help with prognosis and monitoring. CA-125 and HE4 are ovarian markers.
Chronic primary cold agglutinin disease in an older adult is most often associated with:
Primary cold agglutinin disease is now seen as a low-grade clonal B-cell disorder, usually producing IgM kappa anti-I. Mycoplasma causes a transient, secondary polyclonal cold agglutinin, and IgG anti-P is the Donath–Landsteiner antibody.