Introduction The development of iron deficiency anaemia is well recognised as an early presentation of colorectal cancer. The World Health Organisation defines anaemia as a haemoglobin of <13 g/dl in men and 12 g/dl in women. The presence of a low ferritin is the most powerful test for iron deficiency with a ferritin of <50 μg/l consistent with this diagnosis. Recent literature suggests that a lower limit of 100 μg/l is more sensitive when considering a diagnosis of colorectal cancer. In iron deficiency anaemia, red cells classically have a low mean cell volume (MCV).

The aims of this study are fourfold:

• To evaluate the change in haemoglobin in the 2 years prior to colorectal cancer diagnosis

• To gauge the adequacy of investigation of anaemia

• To assess the correlation between ferritin and colorectal cancer in anaemic patients

• To explore the relationship between MCV and low ferritin

Methods The records of 194 patients diagnosed with colorectal cancer between April 2007 and September 2009 were reviewed retrospectively. Haemoglobin, ferritin and MCV within the previous 2 years were recorded.

Results 186 patients had a previous haemoglobin available. 76 patients (41%) were anaemic prior to diagnosis and a further 25 (13%) had a 10% drop in haemoglobin from baseline. 18% of these patients had a low MCV. No patients had an elevated MCV. Of the 101 patients with anaemia or a 10% haemoglobin drop, 37 (37%) had iron studies performed. Ferritin was <50 μg/l in 73% of cases and <100 μg/l in 97%. A normal MCV was found in 64% of patients with a ferritin of <100 μg/l.

The median time from presentation of anaemia to diagnosis of colorectal cancer was 3 months but 24 patients had a delay of between 12 and 24 months. The median time to diagnosis was the same for patients with a low ferritin or a 10% drop in haemoglobin.

Conclusion In the 2 years preceding colorectal cancer diagnosis, 41% of patients develop anaemia and a further 13% have a 10% drop in haemoglobin. This remains poorly investigated. A normal MCV is falsely reassuring and patients meeting developing anaemia or a 10% drop in haemoglobin should have iron studies performed. This study confirms recent findings that a lower limit for ferritin of 100 mcg/l is more sensitive when considering colorectal cancer.

24% of patients wait 12–24 months between the development of anaemia or a 10% drop in haemoglobin and a diagnosis of colorectal cancer. This percentage could be significantly reduced by the timely investigation of these patients with iron studies. Referral for urgent GI investigations should be made for patients with a ferritin <100 μg/l and no overt blood loss from another source.