MLT GlobeDHA exam preparation (Dubai) – page 23
700 practice MCQs for the DHA medical laboratory exam. Level: Basic to intermediate.
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.
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.
In hereditary spherocytosis, which membrane protein is most often affected?
Ankyrin-1 defects are the most frequent cause of hereditary spherocytosis, weakening vertical links between the lipid bilayer and the spectrin skeleton. Protein 4.1R defects mainly cause hereditary elliptocytosis, not spherocytosis.
Patients with pyruvate kinase deficiency often tolerate their anemia better than expected because:
The block at pyruvate kinase causes upstream accumulation of 2,3-BPG, which lowers hemoglobin oxygen affinity and improves oxygen delivery to tissues. ATP is decreased, not raised, in this enzyme defect.
A sickle solubility test on a 3-month-old infant with sickle cell disease is negative. The most likely reason is:
Before about 6 months of age, HbF is still high and HbS is too low to produce turbidity, giving false negatives. Newborn and infant screening therefore uses electrophoresis or HPLC instead.
Only a light-blue citrate tube is ordered and a winged (butterfly) set is used. What should the phlebotomist do first?
Air in the winged-set tubing would underfill the citrate tube, so a discard tube (plain or citrate) is drawn first. EDTA before citrate risks additive carryover.
In the Clauss fibrinogen method, diluted plasma is clotted with excess thrombin. The clotting time is:
With high thrombin, the clotting time depends on fibrinogen: the lower the fibrinogen, the longer the time. Results are read from a calibration curve.
In a dilute Russell viper venom time (dRVVT) test, which pattern supports lupus anticoagulant?
LA antibodies are phospholipid-dependent; excess phospholipid in the confirm reagent overcomes them, shortening the time. ISTH advises pairing dRVVT with an LA-sensitive aPTT.
A pregnant woman on twice-daily subcutaneous LMWH needs monitoring. The best test and timing is:
LMWH has little effect on the aPTT; anti-Xa is measured at peak, about 4 hours after subcutaneous dosing. INR is used for warfarin.
A patient has EDTA-dependent platelet clumping. A recollected sodium citrate sample gives a platelet count of 90 × 10^9/L. The reported count should be:
The citrate tube dilutes blood 9:10, so the count is multiplied by 1.1: 90 × 1.1 = 99 × 10^9/L. Reporting 90 underestimates the count.
Aggregation studies show absent response to arachidonic acid, reduced secondary wave with epinephrine and ADP, and normal ristocetin. The most likely cause is:
Aspirin blocks COX-1, preventing thromboxane A2 formation from arachidonic acid. Glanzmann thrombasthenia would abolish ADP, epinephrine and collagen responses completely.
An anemic patient has a reticulocyte production index (RPI) of 1.2. This most likely indicates:
An RPI below 2 in an anemic patient means the marrow is not responding adequately, e.g. iron deficiency, marrow failure or renal disease. An RPI above 3 suggests hemolysis or blood loss with a normal marrow.
A patient with severe megaloblastic anemia has raised LDH and raised unconjugated bilirubin. These findings are mainly due to:
Many megaloblastic precursors die in the marrow before release (ineffective erythropoiesis), releasing LDH and hemoglobin breakdown products. This is intramedullary, not immune or complement-mediated hemolysis.
A red cell with two horn-like projections forms when:
Keratocytes (horn cells) form when a vacuole near the edge ruptures, often in microangiopathic states such as DIC. Removal of a Heinz body by the spleen produces a bite cell.
Target cells form when:
Excess membrane (e.g. cholesterol loading in liver disease) or reduced hemoglobin (thalassemia) leaves extra membrane that folds into a target shape. A decreased surface-to-volume ratio produces spherocytes instead.
Red cells appear in clumps on a wet preparation. After adding saline, the clumps disperse. This indicates:
Rouleaux are caused by high plasma proteins and break up when plasma is replaced or diluted with saline. True agglutination is antibody-mediated and persists after saline replacement.
In CML monitoring by RQ-PCR, a major molecular response (MMR) is defined as a BCR::ABL1 level on the International Scale of:
MMR (MR3) is a 3-log reduction, i.e. BCR::ABL1 ≤0.1% IS. ≤1% corresponds roughly to complete cytogenetic response, and ≤0.0032% is the deeper MR4.5.
A patient has erythrocytosis, low serum erythropoietin and a negative JAK2 V617F test. Which additional test is most useful to support polycythemia vera?
About 3% of PV cases lack V617F but carry JAK2 exon 12 mutations. CALR and MPL mutations are found in ET and PMF, not PV.
An elderly woman has macrocytic anemia, normal-to-high platelets, <5% marrow blasts and hypolobated megakaryocytes. Karyotype shows a single deletion of 5q. This subtype of MDS is known for:
MDS with isolated del(5q) has a relatively good prognosis and responds well to lenalidomide. ATRA is used for APL, not MDS.
In the WHO 5th edition, a low-blast myelodysplastic neoplasm with ring sideroblasts is defined mainly by a mutation in which gene?
SF3B1 mutations are strongly linked to ring sideroblasts; WHO 5th names this entity MDS with low blasts and SF3B1 mutation. NPM1 mutation defines an AML type.