MLT GlobeASCP exam preparation (USA · MLS / MLT) – page 4
1200 practice MCQs for the ASCP medical laboratory exam. Level: Advanced.
When reading a microhematocrit, including the buffy coat in the red cell column will:
Only the packed red cell column should be read; the buffy coat of white cells and platelets adds to the reading. A falsely high Hct would lower the calculated MCHC, not raise it.
G6PD deficiency is inherited as which pattern?
The G6PD gene lies on the X chromosome, so males are usually affected and females are carriers, although some heterozygous females are affected due to lyonization. Pyruvate kinase deficiency, not G6PD deficiency, is autosomal recessive.
In paroxysmal nocturnal hemoglobinuria, red cells are sensitive to complement because they lack:
An acquired PIGA mutation prevents GPI-anchor synthesis, so the GPI-linked complement regulators CD55 (DAF) and CD59 (MIRL) are missing. CD34 and CD38 are stem cell and maturation markers unrelated to complement control.
A 4-year-old develops acute kidney injury, thrombocytopenia and schistocytes one week after bloody diarrhea. The most likely cause is:
Typical hemolytic uremic syndrome follows infection with Shiga toxin-producing E. coli such as O157:H7, with toxin damaging renal endothelium. C. difficile causes colitis but not classic HUS.
Hb Bart's hydrops fetalis results from which alpha-globin genotype?
With no functional alpha genes, the fetus makes only gamma-4 tetramers (Hb Bart's), which cannot deliver oxygen, leading to hydrops. The --/-α genotype causes HbH disease, which is compatible with life.
An aPTT reagent contains which components added to citrated plasma?
The aPTT uses phospholipid (partial thromboplastin) plus an activator such as silica, kaolin or ellagic acid, then calcium. Tissue factor is the PT reagent.
Bleeding from a platelet defect, rather than a coagulation factor deficiency, typically presents as:
Platelet and VWF disorders cause immediate mucocutaneous bleeding and petechiae. Hemarthroses and delayed bleeding suggest factor deficiencies such as hemophilia.
A patient has a hematocrit of 0.30 L/L (30%) and an RBC count of 4.0 × 10^12/L. What is the MCV?
MCV (fL) = Hct (%) × 10 ÷ RBC (× 10^12/L) = 300 ÷ 4.0 = 75 fL. 133 fL results from dividing the RBC count by the hematocrit incorrectly.
Hemoglobin is 12.0 g/dL and hematocrit is 36%. What is the MCHC?
MCHC (g/dL) = Hb (g/dL) × 100 ÷ Hct (%) = 1200 ÷ 36 = 33.3 g/dL (333 g/L), which is within the normal range.
What does the red cell distribution width (RDW) measure?
RDW is the coefficient of variation (or SD) of the RBC volume distribution, so it is a numerical measure of anisocytosis. It does not measure shape (poikilocytosis) or hemoglobin content.
A 25-year-old has pancytopenia, a reticulocyte count of 0.2% and a bone marrow trephine that is mostly fat with few hematopoietic cells. No abnormal cells are seen. The most likely diagnosis is:
Pancytopenia with very low reticulocytes and a hypocellular fatty marrow without infiltration is aplastic anemia. Megaloblastic anemia and leukemia usually give a hypercellular marrow.
In a normal red cell on a well-made smear, the central pallor occupies about:
Normal discocytes show central pallor of about one third of the diameter. Pallor larger than this indicates hypochromia, and a thin rim of hemoglobin is seen in severe hypochromia.
Classic Reed-Sternberg cells of classic Hodgkin lymphoma typically show which immunophenotype?
Hodgkin/Reed-Sternberg cells are usually CD30+ and CD15+ with loss of CD45. Nodular lymphocyte-predominant cells are CD20+ and CD45+.
A Caribbean-born adult has hypercalcemia, skin lesions and circulating lymphocytes with multilobed 'flower-shaped' nuclei. The associated virus is:
Adult T-cell leukemia/lymphoma is caused by HTLV-1 and shows CD4+ 'flower cells' and hypercalcemia. EBV is linked to Burkitt and Hodgkin lymphoma.
In granulocyte maturation, secondary (specific) granules first appear at which stage?
Specific granules first appear in the myelocyte, allowing neutrophil, eosinophil and basophil lines to be told apart. Promyelocytes contain mainly primary (azurophilic) granules.
A large cell has a folded, horseshoe-shaped nucleus with lacy chromatin and grey-blue 'ground-glass' cytoplasm with fine granules and vacuoles. It is most likely a:
Monocytes have folded nuclei, lacy chromatin and grey-blue cytoplasm with fine azurophilic dust and vacuoles. Reactive lymphocytes have deeper blue cytoplasm and denser chromatin.
A WBC count is 12.0 × 10^9/L and the differential shows 55% lymphocytes. The absolute lymphocyte count is:
Absolute count = WBC × percentage = 12.0 × 0.55 = 6.6 × 10^9/L. Reporting only the percentage can hide true absolute changes.
Rheumatoid factor detected by latex agglutination is usually an antibody of which class directed against which target?
Classic RF is IgM directed against the Fc portion of IgG. Latex particles coated with human IgG are agglutinated by IgM RF.
Which cell surface marker is most characteristic of mature helper T lymphocytes?
Helper T cells express CD3 and CD4 and recognise antigen presented on MHC class II. CD8 marks cytotoxic T cells, CD19 marks B cells and CD56 marks NK cells.
Which marker is a pan-B-cell antigen commonly used in flow cytometry to count B lymphocytes?
CD19 is expressed from early B-cell development until the plasma-cell stage. CD2 and CD7 are T-cell markers; CD33 is a myeloid marker.