MLT GlobeChemistry: Tumor markers & iron studies – page 3
59 Chemistry MCQs on Tumor markers & iron studies with answers and explanations.
A woman in the third trimester of pregnancy has normal iron stores. Which iron study result is expected to be increased because of pregnancy itself?
Estrogen increases hepatic transferrin synthesis, so TIBC rises in pregnancy and with oral contraceptives, even without iron deficiency. Ferritin tends to fall during pregnancy.
A child has prolonged fever, splenomegaly, pancytopenia and a serum ferritin of 25,000 µg/L (ng/mL). Which condition is most strongly suggested?
Extremely high ferritin with fever, cytopenias and splenomegaly is typical of HLH, caused by uncontrolled macrophage activation. Iron deficiency gives a low ferritin.
When iron supply to developing red cells is inadequate, which substance increases in red cells?
Without enough iron, ferrochelatase inserts zinc into protoporphyrin, so zinc protoporphyrin rises in iron deficiency (and in lead poisoning). Hemosiderin is a storage form that falls in iron deficiency.
Which hematology analyser parameter gives an early measure of iron available for new red cells over the past few days?
Reticulocytes circulate for only 1–2 days, so their hemoglobin content reflects current iron supply to the marrow. MCHC changes late because mature cells live about 120 days.
Serum iron is 20 µmol/L and unsaturated iron-binding capacity (UIBC) is 55 µmol/L. What is the transferrin saturation?
TIBC = serum iron + UIBC = 20 + 55 = 75 µmol/L. Saturation = 20 ÷ 75 × 100 = 26.7%, about 27%. Dividing iron by UIBC instead gives 36%.
PSA was undetectable after radical prostatectomy but is now rising on repeat tests. This most suggests:
After the whole prostate is removed, PSA should stay undetectable. A confirmed rising PSA indicates residual or recurrent prostate cancer (biochemical recurrence).
A woman with iron deficiency anemia starts oral iron. Which is the earliest laboratory sign of response, usually seen within about 1 week?
The marrow responds quickly, and reticulocytes rise within about 5–10 days. Hemoglobin takes weeks to normalise, and ferritin refills stores only after months.
A patient has microcytic red cells with normal serum iron and normal ferritin. Which condition is more likely than iron deficiency?
Microcytosis with normal iron studies suggests a globin synthesis defect such as thalassemia trait. B12 and folate deficiency and liver disease cause macrocytosis.
A man taking finasteride (5-alpha-reductase inhibitor) for 1 year has a PSA of 2.0 ng/mL. How is this usually interpreted?
5-alpha-reductase inhibitors lower PSA by about 50% after 6–12 months. Doubling the value is a common way to compare with usual reference limits.
A man with a testicular tumor diagnosed as pure seminoma on biopsy has a clearly raised serum AFP. This suggests:
Pure seminoma does not produce AFP (it may produce some hCG). A raised AFP points to a nonseminomatous germ cell element, which changes treatment.
A woman with suspected molar pregnancy has an hCG result much lower than expected. After a 1:100 dilution the result is very high. This is due to:
In one-step sandwich assays, huge antigen excess saturates both antibodies and gives a falsely low signal. Dilution brings the level into range and reveals the true high value.
A non-pregnant woman has a persistently low positive serum hCG, but urine hCG is negative, and results change with different assays. The likely cause is:
Heterophile (anti-animal) antibodies bridge assay antibodies in serum and give 'phantom hCG'. They do not pass into urine, so urine hCG is negative.
A patient with pancreatic cancer has an undetectable CA 19-9. Which explanation is most likely?
CA 19-9 is a sialylated Lewis a antigen; Lewis-negative people cannot make it. Biliary obstruction usually raises CA 19-9, not lowers it.
Which test helps separate iron deficiency from anemia of chronic disease because it rises in iron deficiency but is little affected by inflammation?
Iron-deficient erythroid cells express more transferrin receptors, raising sTfR; inflammation has little effect. Ferritin, by contrast, rises in inflammation.
In common colorimetric methods for serum iron (e.g. ferrozine), which step comes before color formation?
Acid releases Fe3+ from transferrin, a reducing agent converts it to Fe2+, and Fe2+ then forms a colored complex with the chromogen. Chromogens like ferrozine react with ferrous, not ferric, iron.
Which three serum markers are used in the "S" (serum marker) category of TNM staging for testicular germ cell tumors?
AFP, hCG and LDH levels after orchiectomy define the S category and help with prognosis and monitoring. CA-125 and HE4 are ovarian markers.
A patient being tested for a neuroendocrine tumor has a raised chromogranin A. Which medication is a well-known cause of a false-positive result?
Proton pump inhibitors cause high gastrin, which stimulates enterochromaffin-like cells to release chromogranin A. The drug is usually stopped for a period before testing when safe.
After total thyroidectomy for papillary thyroid cancer, serum thyroglobulin is undetectable. Why must anti-thyroglobulin antibodies also be measured?
Thyroglobulin antibodies are present in many patients and interfere with sandwich immunoassays, usually giving falsely low results that could hide recurrence. Medullary cancer is followed with calcitonin.
Serum transferrin is 2.4 g/L. Using TIBC (µmol/L) ≈ transferrin (g/L) × 25, the estimated TIBC is about:
Each transferrin molecule binds two iron atoms, giving the factor of about 25. 2.4 × 25 = 60 µmol/L (about 335 µg/dL). Using 12.5 would give only the transferrin molar value, not binding capacity.