Hematology & Coagulation Flashcards

A patient has giant platelets, thrombocytopenia, and absent ristocetin aggregation that is NOT corrected by adding normal plasma. The most likely diagnosis is:

Answer: Bernard-Soulier syndrome

Bernard-Soulier syndrome is a GP Ib/IX/V deficiency, so the platelets cannot bind VWF; normal plasma does not help because the defect is in the platelet.

Glanzmann thrombasthenia results from a deficiency of which platelet glycoprotein?

Answer: GP IIb/IIIa

Without GP IIb/IIIa, platelets cannot bind fibrinogen, so aggregation to ADP, collagen, and epinephrine is absent but ristocetin response is normal.

On alkaline (pH 8.6) cellulose acetate electrophoresis, hemoglobin S migrates with which other hemoglobin?

Answer: Hb D

Hb S, D, and G share the same position at alkaline pH, so acid citrate agar or a solubility test is needed to tell them apart.

An EDTA sample shows a platelet count of 40 x 10^3/µL, and the smear reveals platelet clumps. What is the best next step?

Answer: Recollect in a sodium citrate tube

EDTA-dependent platelet clumping causes pseudothrombocytopenia; recollecting in citrate and correcting for dilution gives an accurate count.

A microcytic patient has an MCV of 62 fL and an RBC count of 6.1 x 10^6/µL (Mentzer index about 10). This pattern most suggests:

Answer: Thalassemia trait

A Mentzer index (MCV/RBC) below 13 favors thalassemia trait, in which the RBC count is high relative to the degree of microcytosis.

Seven days after starting unfractionated heparin, a patient's platelet count falls by 60% and a new DVT develops. What is the most appropriate action?

Answer: Stop all heparin and start a non-heparin anticoagulant

Suspected HIT requires stopping all heparin, including LMWH because of cross-reactivity, and starting an agent such as argatroban.

Using the rule of three, a hemoglobin of 12.0 g/dL should correspond to a hematocrit of about:

Answer: 36%

For normocytic, normochromic cells, Hct is about Hgb x 3, so 12.0 x 3 = 36%.