“The blood service turned me away for low iron — but I feel completely fine”

The incidental-findings principle: a result generated by another service (here, a blood-donation deferral for a low haemoglobin) lands with the GP, who now OWNS the duty to act — "I feel fine / it’s a non-event" must be resisted, and the finding worked up as if the patient had presented with symptoms. Confirmed iron-deficiency anaemia (low Hb, low MCV, low ferritin) in a MAN of any age, or in any postmenopausal woman, is gastrointestinal blood loss / malignancy until proven otherwise — because men do not menstruate, the lost iron must be sourced — commonly a right-sided colorectal cancer (which bleeds occultly and presents with anaemia, not visible bleeding), gastric cancer, or benign causes (NSAID gastropathy, angiodysplasia, coeliac). NICE HTG690: offer quantitative FIT in adults with IDA, and NICE NG12 (Suspected cancer: recognition and referral, last updated April 2026): FIT ≥10 µg Hb/g → suspected cancer pathway colorectal referral (FIT now guides the referral; a low FIT does not close the case if concern persists); investigate BOTH ends with bidirectional endoscopy (OGD + colonoscopy; BSG 2021) for unexplained IDA; and check coeliac serology (anti-tTG). Review regular NSAID use as a contributor WITHOUT assuming it is the whole story (it can coexist with cancer), and give iron replacement alongside — never instead of — investigation, since replacing iron and sending him back to donate masks the cause and delays diagnosis. Honour the proud-donor identity while holding the line that investigation precedes any return to donation, take the targeted GI history (treating darker stools and bowel-habit change as positive cues), and safety-net and follow up.