Aim-To describe a new inexpensive method (the WHO Colour Scale) for estimating haemoglobin concentration from a drop of blood by means of a colour scale, and to compare its reliability with a standard laboratory method of measuring haemoglobin, and its clinical usefulness in field trials. Methods-The new colour scale method was used to measure haemoglobin concentration in 1213 random venous blood samples from routine work in four laboratories (one each in the UK, South Africa, Thailand, and Switzerland). Limited field trials of the method for assessing clinical usefulness were done in a rural hospital (in South Africa) staVed by nurses, at two blood donor sessions (one each in South Africa and Thailand), and by nonlaboratory personnel in malaria clinics (in Thailand), following training and a short practice session. Results-In the laboratory based comparability study the presence of anaemia was reliably detected using the new method with 91% sensitivity and 86% specificity. Clinically relevant levels of anaemia (mild to moderate, pronounced, and severe) were graded and serious anaemia (< 8 g/ dl) was identified with an eYciency of 89%. The clinical trials showed the ease and reliability with which the colour scale could be used by non-laboratory persons after brief training. The blood donor trials showed it to be at least as reliable as the copper sulphate method with the advantage of being more convenient. Conclusions-The preliminary studies have shown that the WHO Colour Scale is a reliable screening method for detecting anaemia, especially for diagnosing serious anaemia. Following a brief training session health workers found it simple to use and, at a cost of about 1/10th that for traditional photometric analysis, it should be of value in "countries in need" for primary health centres, obstetrical management, paediatric clinics, tropical disease control programmes, blood transfusion donor selection, as well as for industrial health checks and epidemiological studies. (J Clin Pathol 1998;51:21-24)

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