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Hematology and Coagulation Flashcards

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  1. A peripheral blood smear review is triggered by a 'Nucleated RBC' flag on an automated hematology analyzer. The technologist counts 8 NRBCs per 100 WBCs. The analyzer reported a total WBC count of 12.0 x 10^9/L. What is the corrected WBC count?

    Answer: 11.1 x 10^9/L

    Automated hematology analyzers using certain technologies can misclassify nucleated red blood cells (NRBCs) as white blood cells (WBCs) because both have nuclei. This leads to a falsely elevated WBC count. A manual differential and NRBC count allows for a mathematical correction using the formula: Corrected WBC = (Uncorrected WBC x 100) / (100 + Number of NRBCs/100 WBCs). In this case, (12.0 x 100) / (100 + 8) = 1200 / 108 = 11.1 x 10^9/L.

  2. A patient presents with a microcytic anemia. The CBC results are as follows: HGB 105 g/L, MCV 65 fL, RBC 5.5 x 10^12/L, RDW 14.0%. Serum ferritin is normal. Which of the following conditions is most likely?

    Answer: Beta-thalassemia trait

    In beta-thalassemia trait, there is a defect in beta-globin chain production, leading to small (low MCV) and poorly hemoglobinized red cells. The bone marrow compensates by increasing the production of RBCs, resulting in a characteristically high or normal RBC count relative to the hemoglobin level. Iron deficiency anemia also presents with microcytosis, but typically the RBC count is decreased, and the RDW is often elevated. Normal ferritin rules out iron deficiency.

  3. A patient has a prolonged activated partial thromboplastin time (APTT). A 1:1 mixing study is performed. The immediate APTT on the mix corrects into the normal range, but after a 2-hour incubation at 37°C, the APTT of the mixture becomes prolonged again. This pattern is most characteristic of:

    Answer: A time- and temperature-dependent inhibitor, such as anti-Factor VIII

    The initial correction of the APTT upon mixing with normal plasma suggests a factor deficiency. However, the subsequent prolongation after incubation indicates the presence of an inhibitor that requires time and temperature to inactivate the corresponding factor in the normal plasma. This is the classic presentation of a specific factor inhibitor, most commonly against Factor VIII.

  4. The presence of Auer rods within blasts on a peripheral blood smear is most strongly associated with which of the following conditions?

    Answer: Acute Myeloid Leukemia (AML)

    Auer rods are needle-like, azurophilic cytoplasmic inclusions that are pathognomonic for myeloid blasts. They are formed from the abnormal fusion of primary granules. While not present in all cases of Acute Myeloid Leukemia (AML), their presence confirms a myeloid lineage and is a key morphological feature for diagnosing AML, particularly the acute promyelocytic leukemia (APL) subtype.

  5. A patient's sample run on a hematology analyzer at room temperature (22°C) produces an MCHC of 390 g/L and a very low RBC count. A peripheral smear shows large, irregular clumps of red blood cells. What is the most appropriate next step to obtain accurate CBC results?

    Answer: Warm the sample to 37°C for 15-30 minutes and rerun

    The combination of a high MCHC, low RBC count, and visible RBC agglutination on the smear is characteristic of cold agglutinin disease. The IgM antibodies responsible for this cause RBCs to clump at temperatures below body temperature, leading to spurious results from automated analyzers. Warming the sample to 37°C will cause the agglutinins to dissociate from the RBCs, allowing for an accurate count.

  6. A physician is evaluating a patient with a low pre-test probability for venous thromboembolism (VTE). Which of the following laboratory tests is most useful for ruling out this condition?

    Answer: D-dimer

    The D-dimer test measures a specific degradation product of a cross-linked fibrin clot. It has a high negative predictive value, meaning a normal or negative result in a patient with low clinical suspicion makes the presence of a recent major clot (like DVT or PE) highly unlikely. Its high sensitivity and low specificity make it an excellent test for exclusion, but not for confirmation, of VTE.