Introduction Colonoscopy is frequently performed in patients presenting with melaena who have a negative upper gastrointestinal endoscopy (UGIE). Published literature suggests a diagnostic yield of 8%–30%, the most common pathologies being colonic angiodysplasia and right-sided tumours. However these conditions often give rise to occult haemorrhage and a microcytic profile before patients present with overt bleeding. In patients presenting de novo with melaena a raised urea is known to be predictive of upper GI haemorrhage before any endoscopic assessment. Our aim was to examine the value of colonoscopy in the subgroup of patients with a negative UGIE, and to assess whether the absence of a raised blood urea and/or the presence of a microcytic erythrocyte profile at presentation are predictors of positive colonoscopy.

Methods Our reporting software was interrogated for the interval November 2007–October 2011. All cases of colonoscopy where melaena was the main indication, and which were preceded by a negative UGIE were analysed. In addition, we collected data on the admission blood urea and mean corpuscular volume (MCV). Patients for whom altered/fresh rectal bleeding were included in the indications in addition to melaena were excluded.

Results 724 patients had a total of 829 endoscopic evaluations of melena, and of these 62 patients (53% female) with a median age of 69 year (range 27–91) met our inclusion criteria. 6 of 62 (9.6%) had a cause for the melena identified on colonoscopy: cecal angiodysplasia in 2/6, right-sided malignancies in 2/6 and right-sided diverticular bleeds in 2/6. The admission urea was not significantly lower in patients with a positive colonoscopy (median 11.5 mmol/l, range 5.1–14.7) compared to those with a negative colonoscopy (median 7.2 mmol/l, range 1.4–33.6) (p=0.43). Admission MCV however was significantly lower in patients with a colonic haemorrhage (median 77 fL, range 64–89) compared to patients with a negative colonoscopy (median 90 fL, range 66–116) (p=0.012), with 3/6 (50%) having a low MCV compared to 5/56 (8.9%) of those with a negative colonoscopy (normal = 84–99 fL).

Conclusion The diagnostic yield of colonoscopy in patients with melaena and a non-contributory UGIE in our centre was low (9.6%). A normal/low blood urea on admission did not predict a positive diagnosis for the haemorrhage at colonoscopy in our cohort. However, patients with a colonic source of bleeding had a significantly lower MCV, suggesting a chronic natural history for such right sided colonic haemorrhages.

Competing interests None declared.

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