MLT GlobeHematology: RBC indices & anemias – page 6
138 Hematology MCQs on RBC indices & anemias with answers and explanations.
A 62-year-old man is found to have iron deficiency anemia. He has no obvious bleeding. The most appropriate next step is to:
In adult men and post-menopausal women, iron deficiency is usually caused by chronic blood loss, most often from the gut, including colorectal cancer. Finding the cause is essential.
After starting oral iron for iron deficiency anemia, the reticulocyte count is expected to peak at about:
A reticulocyte response starts in a few days and peaks at about 7–10 days. Hemoglobin then rises by roughly 1–2 g/dL every 2–3 weeks; refilling stores takes about 3 months of therapy.
Why can serum ferritin be normal in a patient with iron deficiency and active infection?
Ferritin rises with inflammation, liver damage and malignancy, so a 'normal' ferritin may hide iron deficiency. Many guidelines use a higher cut-off (e.g. <100 µg/L) when inflammation is present.
On most impedance hematology analyzers, the hematocrit is not measured directly. It is calculated from:
Impedance analyzers measure RBC count and MCV (mean pulse height); Hct (%) = MCV (fL) × RBC (10^12/L) ÷ 10. The MCHC is then derived from Hb and this calculated Hct, not the other way round.
A red cell volume histogram has a standard deviation of 11.2 fL and an MCV of 80 fL. What is the RDW-CV?
RDW-CV = (SD ÷ MCV) × 100 = (11.2 ÷ 80) × 100 = 14.0%. The value 11.2 is the RDW-SD-type figure in fL, not the CV.
Zinc protoporphyrin (ZPP) in red cells rises when zinc is inserted into protoporphyrin instead of iron. ZPP is typically increased in:
ZPP rises when iron is unavailable (iron deficiency) or ferrochelatase is blocked (lead). It is usually normal in thalassemia trait, which helps separate it from iron deficiency.
Lead causes anemia mainly by inhibiting which two enzymes of heme synthesis?
Lead inhibits ALA dehydratase (raising urinary ALA) and ferrochelatase (raising ZPP). Heme oxygenase and biliverdin reductase act in heme breakdown, not synthesis.
Which vitamin B12 test measures the fraction that cells can take up and is considered an early marker of deficiency?
Only B12 bound to transcobalamin (about 20–30% of total) is delivered to cells, and it falls early in deficiency. Most serum B12 is on haptocorrin, which cells cannot use.
A patient develops megaloblastic anemia and numb legs after repeated recreational nitrous oxide use. Nitrous oxide causes this by:
Nitrous oxide oxidizes the cobalt of cobalamin, inactivating methionine synthase and causing functional B12 deficiency even with normal serum B12. Dihydrofolate reductase is inhibited by methotrexate, not nitrous oxide.
A patient with undiagnosed vitamin B12 deficiency is treated with folic acid alone. The most likely result is:
Large doses of folic acid can partly correct the megaloblastic anemia, but they do not treat B12-dependent nerve damage, which may worsen. B12 status should be checked before giving folate.
A patient with brisk hemolysis has an MCV of 104 fL with normal B12 and folate. The most likely reason for the raised MCV is:
Reticulocytes are about 20% larger than mature red cells, so marked reticulocytosis raises the MCV. Spherocytes and iron deficiency tend to lower, not raise, the MCV.
In a healthy term infant, the hemoglobin normally falls to its lowest point (physiological anemia of infancy) at about:
After birth, higher oxygen levels suppress erythropoietin, so Hb falls to a nadir of about 9.5–11 g/dL at around 2–3 months. It then rises as erythropoiesis restarts.
A woman taking an estrogen-containing oral contraceptive has a raised TIBC, normal ferritin and normal Hb. The most likely explanation is:
Estrogen (and pregnancy) increases transferrin production, raising TIBC without iron deficiency. Iron deficiency would lower ferritin, and hemochromatosis or inflammation lowers TIBC.
A man has a major bleed from a peptic ulcer. One hour later he is hypotensive, but his Hb is 14.0 g/dL (140 g/L). The best explanation is:
In acute bleeding, red cells and plasma are lost together, so Hb stays near normal at first. It falls over 24–72 hours as tissue fluid or IV fluid expands plasma volume.
In developing iron deficiency, which CBC parameter often becomes abnormal before the MCV falls below the reference range?
As iron-restricted erythropoiesis starts, a population of smaller cells appears and the RDW rises while the average MCV is still normal. MCHC is usually the last index to fall.
A woman with iron deficiency anemia shows no rise in Hb after 6 weeks of correctly taken oral iron and has no ongoing bleeding. Which condition should be tested for as a cause of poor iron absorption?
Celiac disease damages the duodenal mucosa where iron is absorbed and is a common cause of oral iron failure. The other conditions do not impair iron absorption.
How does serum erythropoietin (EPO) usually differ between secondary polycythemia due to chronic hypoxia and polycythemia vera (PV)?
In hypoxia-driven secondary polycythemia the kidney makes more EPO, so levels are normal or high. In PV the clone grows independently of EPO, and feedback suppresses EPO to low levels.
In iron deficiency anemia, the serum soluble transferrin receptor (sTfR) level is typically:
Iron-starved erythroid cells express more transferrin receptors, so sTfR rises in iron deficiency. In anemia of chronic inflammation it is usually normal, which helps separate the two.
A sample has an RBC count of 5.0 × 10^12/L and an MCV of 90 fL. What is the calculated hematocrit?
Hct (%) = RBC (× 10^12/L) × MCV (fL) ÷ 10 = 5.0 × 90 ÷ 10 = 45%.
The first and rate-limiting enzyme of heme synthesis, ALA synthase, needs which vitamin-derived cofactor?
ALA synthase uses pyridoxal phosphate. This is why some sideroblastic anemias respond to pyridoxine.