A 60-year-old man presents with painless obstructive jaundice. CECT shows a periampullary tumour. Serum CA 19-9 is 850 U/mL. He is found to have blood group O. The CA 19-9 result must be interpreted with caution because:
- A Individuals who are Lewis antigen-negative (Le a-b- phenotype) cannot synthesize CA 19-9 regardless of malignancy
- B Blood group O independently suppresses CA 19-9 production by pancreatic cells
- C Obstructive jaundice can falsely elevate CA 19-9 by up to 10-fold ✓
- D CA 19-9 is only elevated in pancreatic ductal adenocarcinoma, not periampullary tumours
Explanation
Obstructive jaundice per se causes a marked, non-malignant elevation of CA 19-9, sometimes by 10-fold or more over baseline, due to impaired biliary excretion of this sialyl Lewis antigen. Therefore a CA 19-9 of 850 U/mL in the presence of obstructive jaundice cannot reliably distinguish malignancy from benign biliary obstruction. CA 19-9 should be re-evaluated after biliary decompression and resolution of jaundice. Option A is a real biological caveat (Lewis-null individuals cannot produce CA 19-9) but it is not the reason to be cautious in THIS patient presenting WITH an elevated CA 19-9.
Reference: Bailey & Love's Short Practice of Surgery, 27th ed.
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Written and medically reviewed by the StethoPrep medical team.