A patient with suspected prostate cancer has a total PSA of 9 ng/mL. The free PSA:total PSA ratio is 0.08 (8%). Which interpretation is CORRECT?
- A Low free:total PSA ratio increases the likelihood of malignancy and warrants biopsy ✓
- B Low free:total PSA ratio favours benign prostatic hypertrophy
- C Free PSA fraction is elevated in prostate carcinoma
- D The ratio is not useful when total PSA is below 10 ng/mL
Correct answer: A. Low free:total PSA ratio increases the likelihood of malignancy and warrants biopsy
Explanation
In prostate carcinoma, PSA is predominantly complexed to alpha-1-antichymotrypsin, reducing the free fraction; thus a free:total ratio below 10–15% strongly suggests malignancy and guides the decision to biopsy. BPH releases proportionately more free PSA. The free:total ratio is most clinically useful in the diagnostic grey zone of total PSA 4–10 ng/mL, which includes this patient's result.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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