Diagnosing colorectal cancer in primary care: cohort study in Sweden of qualitative faecal immunochemical tests, haemoglobin levels, and platelet counts

Colorectal cancer (CRC) diagnostics are challenging, particularly in primary care. Guidelines in several countries recommend referring patients with alarm symptoms to secondary care for colonoscopy, however the majority of patients with CRC who consult primary care practitioners have no alarm symptoms. Conversely, alarm symptoms are common in patients who do not have any serious diseases. In this Swedish cohort study, the diagnostic usefulness of qualitative faecal immunochemical tests (FITs) requested for symptomatic patients in primary care was evaluated, both alone and combined with findings of anaemia and thrombocytosis. 15,789 patients provided three-sample FITs from one of four brands, requested as diagnostic aids. 304 were diagnosed with CRC within 2 years. The tests showed sensitivities of 81.6%–100% and specificities of 65.7%–79.5%. Calculated for the finding of either a positive FIT or anaemia, the sensitivities improved to 88.9%–100%. Adding thrombocytosis did not further increase the overall diagnostic performance. Overall, qualitative FITs seem to be useful as rule-in tests for referral when CRC is suspected in a primary care setting.

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