MLT GlobeDHA exam preparation (Dubai) – page 24
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
Which marker is considered most specific for T-lineage in acute lymphoblastic leukemia?
Cytoplasmic CD3 is the lineage-defining T-cell marker. CD7 is sensitive but also appears on some myeloid blasts.
A 65-year-old man has lymphocytosis and splenomegaly. Cells are CD19+, CD5+, CD23-negative, FMC7-positive and show bright surface light chain. Which test best confirms the likely diagnosis?
CD5+ CD23– B cells suggest mantle cell lymphoma, confirmed by cyclin D1 overexpression or t(11;14) CCND1::IGH. CLL is CD5+ but CD23+.
Which pair of findings best supports classic hairy cell leukemia rather than its variant?
Classic HCL is CD11c+, CD25+, CD103+, annexin A1+ and nearly always carries BRAF V600E. The variant lacks CD25 and BRAF V600E.
A 62-year-old has serum M-protein 15 g/L (1.5 g/dL), 6% clonal marrow plasma cells, and normal calcium, creatinine, Hb and bones. The best classification is:
MGUS: M-protein <30 g/L, clonal plasma cells <10% and no myeloma-defining events. Smoldering myeloma needs ≥30 g/L M-protein or 10–59% clonal plasma cells.
Basophil granules sometimes appear as empty spaces on a Wright-stained smear because their contents are:
Basophil granules (histamine, heparin) are water-soluble and can wash out during staining, leaving clear areas. This is not a methanol or EDTA effect.
In reversed-phase HPLC with a nonpolar C18 column and a polar mobile phase, which compounds elute first?
In reversed-phase chromatography the stationary phase is nonpolar, so polar compounds interact least and elute first. Nonpolar compounds are retained longer.
A 100 µL pipette is checked gravimetrically with water (assume density 1.000 g/mL). The mean delivered mass is 0.0980 g. The inaccuracy (percent error) is:
Delivered volume = 98.0 µL. Error = (98.0 − 100)/100 × 100 = −2.0%. The gravimetric method converts the weight of delivered water to volume.
In atomic absorption spectrophotometry for lead, the light source is a hollow cathode lamp whose cathode is made of:
The cathode is made of the same element being measured so it emits that element's exact wavelengths, which ground-state atoms in the flame absorb.
A serum creatinine is 1.0 mg/dL. Creatinine has a molecular weight of 113 g/mol. The SI result is approximately:
1.0 mg/dL = 10 mg/L; 10 ÷ 113 = 0.0884 mmol/L = 88.4 µmol/L. 8.8 µmol/L misses the dL-to-L factor of 10.
How much 95% ethanol is needed to prepare 500 mL of 70% ethanol?
V1 = (70 × 500)/95 = 368 mL, made up to 500 mL with water. 350 mL is 70% of 500 and ignores that the stock is only 95%.
A 24-hour urine volume is 1440 mL with a urine creatinine of 100 mg/dL. Plasma creatinine is 1.0 mg/dL. The uncorrected creatinine clearance is:
Clearance = (U × V)/P. V = 1440 mL/1440 min = 1.0 mL/min. (100 × 1.0)/1.0 = 100 mL/min. Using the total volume without converting to per minute is the common error.
A horizontal laminar-flow clean bench is NOT suitable for handling infectious specimens because it:
A clean bench pushes HEPA-filtered air across the work surface toward the operator. It protects the product only and would expose the worker to aerosols from infectious material.
Sodium fluoride in a gray-top tube preserves glucose by inhibiting which glycolytic enzyme?
Fluoride inhibits enolase, stopping glycolysis in blood cells. Hexokinase is used as a glucose assay reagent, not the target of fluoride.
Two consecutive results for the same control level both exceed the +2 SD limit. Which rule is violated and what error does it suggest?
Two consecutive values beyond the same 2 SD limit violate 2-2s, which detects systematic error (bias). R-4s requires values on opposite sides of the mean.
On a Levey-Jennings chart, control values rise steadily over eight days in one direction. The most likely cause is:
A trend is a gradual, progressive change in one direction, typical of slowly deteriorating reagents, lamps or filters. Single events such as a bubble cause isolated outliers, not trends.
A technologist is unsure of a proficiency testing result and wants to send the PT sample to a reference lab to confirm it before reporting. The correct action is to:
Regulations (e.g. CLIA) require PT samples to be tested in the same way as patient samples. Referring PT samples to another lab or discussing results with other labs before submission is prohibited.
According to CLSI EP28, the minimum number of healthy reference individuals recommended to establish a reference interval by the nonparametric method is:
CLSI EP28-A3c recommends at least 120 reference individuals per partition for the nonparametric method. Twenty samples are used only to verify (transfer) an existing interval.
The lowest analyte concentration that can be reliably distinguished from the limit of blank is the:
Per CLSI EP17, LoD is the lowest concentration reliably distinguished from the LoB. LoQ is the lowest concentration measured with acceptable total error; LoB is the highest result expected from a blank.
A 3-month-old has constipation, a weak cry and poor feeding with floppy muscle tone. Which specimen is most useful to confirm infant botulism?
In infant botulism spores germinate in the gut and produce toxin there, so stool (or enema fluid) is tested for toxin and the organism. Serum toxin is often negative in infants.
All disk diffusion QC zones are too large on a new batch of Mueller-Hinton agar plates. Which cause is most likely?
The standard agar depth is about 4 mm; thin agar lets the drug spread further, giving larger zones and false susceptibility. A heavy inoculum gives smaller zones, and 35 °C in air is the correct incubation.