MLT GlobeHematology: Hematology methods & instruments – page 4
83 Hematology MCQs on Hematology methods & instruments with answers and explanations.
A patient's MCV was 88 fL yesterday and is 104 fL today, with no transfusion and normal other parameters in the run. The first thing to investigate is:
MCV changes very slowly because red cells live about 120 days, so a large sudden change fails the delta check and suggests a mislabeled or wrong-patient sample. Nutritional causes cannot change MCV in one day.
In multicolor flow cytometry, compensation is applied to correct for:
Emission spectra overlap, so part of one dye's light is detected in another channel; compensation subtracts this spillover. Fc receptor binding is reduced by blocking, not compensation.
According to ICSH guidance, an EDTA sample for a Westergren-type ESR kept at room temperature should be tested within about:
ESR rises less over time as cells become more spherical, so room-temperature EDTA samples should be tested within about 4 hours (longer only if refrigerated and brought back to room temperature).
A manual 100-cell differential is poor at estimating cell types present in low numbers, such as basophils. The main reason is:
With so few cells counted, random sampling error is large for rare cells; counting more cells or using an analyzer (thousands of cells) improves precision. Basophils do stain with Wright stain.
Blood films made from heparinized blood are unsuitable for routine morphology mainly because heparin:
Heparin causes a blue-tinged background on Romanowsky stains and promotes platelet and leukocyte clumping. EDTA is preferred because it preserves cell morphology best.
In the osmotic fragility test, red cells are placed in graded saline solutions, and the amount of lysis in each tube is measured by:
After incubation and centrifugation, released hemoglobin is read at about 540 nm and expressed as a percentage of full lysis in water. The curve shifts right when fragility is increased.
During a run, an analyzer shows falsely low counts and an abnormal pulse flag. Partial blockage of the counting aperture is suspected. The best first action is:
A partially blocked aperture reduces flow and distorts pulses, so counts and sizes are unreliable. The aperture must be cleaned, performance checked with controls, and affected samples rerun.
Giemsa stain for malaria films is buffered to about pH 7.2 mainly to:
At about pH 7.2, parasite chromatin, cytoplasm and red cell stippling such as Schüffner dots stain well. A more acid buffer may not show the dots.
A thick malaria film is not fixed with methanol before staining because:
Leaving the thick film unfixed lets the water-based stain lyse (dehemoglobinize) the red cells, so parasites in the thick layer can be seen. The thin film is fixed to keep red cells intact.
In the cyanmethemoglobin method, which reagent oxidizes hemoglobin to methemoglobin?
In Drabkin's reagent, potassium ferricyanide oxidizes hemoglobin to methemoglobin, and potassium cyanide then converts it to stable cyanmethemoglobin, read at 540 nm.
Under Westgard rules, a single control result beyond ±3 SD from the mean (a 1-3s violation) means:
A 1-3s violation is a rejection rule. Patient results from that run should not be reported until the error is found and corrected. The 1-2s rule is only a warning.
According to ICSH guidance, what is the minimum internal bore of a Westergren ESR tube?
The Westergren tube is 300 mm long with a bore of at least 2.55 mm; narrower tubes slow sedimentation and give falsely low ESR values.
A 1:20 WBC dilution is charged into a hemocytometer, and 150 cells are counted in 8 large corner squares (both sides). What is the WBC count?
Count × dilution ÷ volume: 150 × 20 ÷ (8 × 0.1 µL) = 3750 cells/µL, which is 3.75 × 10^9/L.
Which hemoglobin derivative is NOT converted to hemiglobincyanide in the reference hemoglobin method?
All common hemoglobin forms except sulfhemoglobin are converted to hemiglobincyanide. Carboxyhemoglobin converts slowly but is still measured.
A sample from a patient with a cryoglobulin shows falsely raised WBC and platelet counts, and precipitate on the smear. The best corrective action is to:
Cryoglobulins precipitate at room temperature and the particles are counted as cells; warming dissolves them. Refrigeration increases the precipitation.
A patient with plasma glucose above 600 mg/dL (33 mmol/L) has a falsely high MCV on an impedance analyzer. The reason is that:
Cells adapted to hyperosmolar plasma take up water in the diluent before sizing, raising MCV and Hct and lowering MCHC. Glucose does not interfere with the hemoglobin absorbance reading.
For a manual platelet count, blood is diluted 1:100 and 250 platelets are counted in the central large squares of both sides of the hemacytometer (total 2 mm², depth 0.1 mm). What is the platelet count?
Platelets/µL = 250 × 100 ÷ (2 × 0.1) = 125,000/µL, or 125 × 10^9/L. 250 × 10^9/L is obtained by counting only one side's area (1 mm²) in the formula.
Using a Miller disc, 30 reticulocytes are counted in the large squares and 200 red cells in the small squares (area one-ninth of the large square). What is the reticulocyte percentage?
Retic % = reticulocytes in large squares ÷ (RBCs in small squares × 9) × 100 = 30 ÷ 1800 × 100 = 1.7%. 15% comes from forgetting to multiply the small-square count by 9.
In analyzers using VCS technology, the radiofrequency (conductivity) measurement mainly gives information about a white cell's:
Low-frequency direct current measures volume, while high-frequency current passes through the membrane and reflects internal contents such as nucleus size and density. Peroxidase activity is measured by cytochemical methods, not conductivity.
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.