MLT GlobeHematology: Hematology methods & instruments – page 3
83 Hematology MCQs on Hematology methods & instruments with answers and explanations.
An analyzer reports RBC 1.8 × 10^12/L, Hb 11.0 g/dL (110 g/L), MCV 128 fL and MCHC 48 g/dL. The smear shows red cell clumps. The next step is to:
Cold agglutinins make red cell clumps count as single large cells, giving a low RBC, high MCV and impossible MCHC; warming disperses the clumps. Plasma replacement is the fix for lipemia, not agglutination.
The WBC count is 20.0 × 10^9/L and 25 nucleated red cells are seen per 100 white cells on the differential. What is the corrected WBC count?
Corrected WBC = WBC × 100 ÷ (100 + nRBC) = 20.0 × 100 ÷ 125 = 16.0 × 10^9/L. 15.0 is obtained by wrongly subtracting 25% of the count.
A patient with severe microcytosis and many red cell fragments has an impedance platelet count higher than the smear estimate. The platelet histogram does not return to baseline near 20 fL. The cause is:
Microcytes and schistocytes fall into the platelet size range, raising the count and lifting the upper end of the histogram. Platelet clumps and giant platelets lower the platelet count instead.
An EDTA sample hemolyzed during collection is analyzed. Which pattern is expected?
Lysed cells are not counted, lowering RBC and calculated Hct, but the released hemoglobin is still measured, so MCH and MCHC rise falsely. Hemoglobin itself is not reduced.
A lavender (EDTA) tube is filled with only a small amount of blood. The microhematocrit is likely to be:
Excess EDTA makes the sample hypertonic, water leaves the red cells and they pack more closely, lowering the spun hematocrit. Swelling occurs with delayed testing, not excess EDTA.
Which finding tends to DECREASE the ESR?
Abnormally shaped cells cannot form rouleaux easily, so they sediment slowly. Anemia and raised fibrinogen or globulins increase the ESR.
During an ESR test the tube is accidentally left tilted a few degrees from vertical. The result will be:
Even a small tilt lets cells slide down the side of the tube and settle faster, raising the ESR noticeably. The tube must stand exactly vertical, free of vibration.
Blood diluted 1:20 is counted in a hemacytometer (depth 0.1 mm). A total of 200 white cells are counted in 4 large squares (4 mm²). What is the WBC count?
Cells/µL = count × dilution ÷ (area × depth) = 200 × 20 ÷ (4 × 0.1) = 10,000/µL, which is 10.0 × 10^9/L. 5.0 results from wrongly using an area of 8 mm² instead of 4 mm².
The immature reticulocyte fraction (IRF) is most useful as:
The IRF reflects the most RNA-rich reticulocytes and rises within days of marrow recovery, often before the neutrophil count. It does not measure iron stores; CHr or Ret-He is used for iron status.
In a manual reticulocyte count with new methylene blue, which inclusion may be wrongly counted as reticulum and falsely raise the result?
Heinz bodies, Howell-Jolly bodies and Pappenheimer bodies take up supravital dye and may be mistaken for reticulum; Heinz bodies appear as pale blue-green round bodies at the edge. Target cells and echinocytes are shape changes and do not stain.
On a CD45 versus side scatter plot for acute leukemia immunophenotyping, blasts typically appear as:
Blasts express less CD45 than mature leukocytes and have few granules, so they fall in the dim CD45, low-SSC 'blast gate'. Bright CD45 with low SSC is the position of mature lymphocytes.
An EDTA sample kept at room temperature for 36 hours before analysis is most likely to show:
With storage, red cells swell, increasing MCV and Hct and lowering MCHC. Hemoglobin is stable, and platelet counts tend to fall, not rise.
A patient with a WBC count of 150 × 10^9/L has an Hb result higher than expected from the Hct and RBC count. This is due to:
Very high leukocyte counts scatter light in the hemoglobin cuvette, falsely raising Hb, MCH and MCHC; the Hb can be read on the centrifuged supernatant. White cells contain no hemoglobin.
A laboratory runs a high-count sample three times followed by a low-count sample three times. The purpose is to check:
Carryover is the contamination of a sample by the one before it; comparing the first and third low-sample results against the high sample estimates it. Linearity is checked with serial dilutions across the reportable range.
A standard microhematocrit is centrifuged at about 10,000–15,000 g. For how long is the tube usually spun?
CLSI guidance uses a high-speed microhematocrit centrifuge for about 5 minutes to reach maximum red cell packing. Much shorter spins leave extra plasma in the column and give falsely high results.
A spun microhematocrit is usually slightly higher than the hematocrit calculated by an analyzer mainly because:
Even after full centrifugation, some plasma remains trapped in the red cell column, so the spun value runs about 1–3% higher. The analyzer calculates Hct from RBC count × MCV and has no trapped plasma.
For a manual RBC count, blood is diluted 1:200. A total of 450 red cells are counted in 5 small squares (each 0.04 mm²) of a hemacytometer 0.1 mm deep. What is the RBC count?
Volume counted = 5 × 0.04 mm² × 0.1 mm = 0.02 µL. Count = 450 × 200 ÷ 0.02 = 4,500,000/µL = 4.5 × 10^12/L. Forgetting the depth or area gives the wrong multiples.
An impedance WBC histogram shows a peak starting at the lower threshold (about 35 fL), and the analyzer flags the region. The most likely cause is:
Nucleated RBC nuclei and large platelet clumps are about the size of small lymphocytes or smaller and create a signal at the lower edge of the WBC histogram. A smear review should confirm the cause.
A patient with HbC disease has many target cells. The WBC count is unexpectedly high and does not match the smear estimate. The most likely cause is:
Target cells in HbC, HbS, thalassemia, liver disease and neonates may resist lysis, and the unlysed stroma is counted as WBCs. Many analyzers flag this; extended lysis or a manual count solves it.
In analyzers that use a peroxidase-staining channel for the WBC differential, which cell type is peroxidase-negative?
Neutrophils and eosinophils stain strongly and monocytes weakly for peroxidase, while lymphocytes (and basophils) are negative. Cells are sorted by peroxidase absorbance and size.