Sir: Having read the letter by Ali and Adeyemo (Psychiatric Bulletin, November 2000, 24, 432), showing the hazards of Clozanil Patient Monitoring Service (CPMS) full blood count monitoring by paying too much attention to the ‘green’ status, I would like to point out another clinically relevant and related pitfall.

One of my patients with chronic schizophrenia, aged 61, has been on clozapine for 3 years. His blood tests were all passed as green. One day we spotted a haemoglobin of 8.5 g on the CPMS form. His normal value had been 13 g. There had been a steady fall over 6 months that nobody had detected as the patient was asymptomatic and the medical staff were focusing on the prominently labelled green status.

The forms themselves did later mention that the haemoglobin was falling, but the warning was condensed on the left side below the blood parameters at the bottom of the form. Asterisks were not used. By contrast, however, the status ‘green’ was in block capitals in open space on the opposite side of the page, drawing the reader's eye to it instantly. This patient has subsequently undergone investigation and treatment for anaemia.

This is another example of a false sense of security gained by relying upon CPMS monthly blood counts. Had they been routine local blood tests then medical staff would have, in my view, assessed each form more thoroughly, paying attention to more than one parameter — as opposed to the solitary concern about a fall in white cell count. The CPMS form needs to have a different layout so as to allow for other abnormalities to be drawn to the doctors' attention sooner.