How objective are the supporters of the Haemoglobin Colour Scale?
Editor The authors of the letter (1) criticising my paper (2) on the Haemoglobin Colour Scale do not declare any conflicts of interest, yet two of them effectively designed the Colour Scale (3). Concerns as to the effect this might have on their impartiality are heightened by their penultimate paragraph comparing me to Marie-Antoinette a comparison that does nothing to assure the reader of the authors' ability to assess evidence impartially and objectively.
Far from being an "innovative" analysis, the Bland-Altman method is accepted as being the appropriate and best method for comparing two assays. The fact that the papers, quoted by the authors of the letter, use a variety of other statistical methods does not disguise the fact that none of them use the appropriate test. Nonetheless, as the authors point out, the results of my study are comparable with those of other studies, and much of the difference lies in the interpretation of the data. In my study over a fifth (22.79%) of the Colour Scale results differed by more than 2g/dl from the reference. In another study (4), and one quoted by the authors of the letter, a third (33%) of results differed by more than 2g/dl. Of greater importance than their statistical significance is that these results are clinically significant; implying that if the Colour Scale is relied on, between a fifth and a third of patients will have wildly inaccurate assessments of their haemoglobin levels. Beyond the rigorous confines of a clinical trial, results with the Colour Scale might be expected to be less accurate and I stand by my conclusion that the poor accuracy of the Haemoglobin Colour Scale renders its use questionable.
Conflicts of interest: none declared.
1. Cherian M, Emmanuel JC, Lewis SM, Montresor A, Farley TMM, Savioli L, & Stott G. Evaluation of the Haemoglobin Colour Scale. Bulletin of the World Health Organization 2002;80:839.
2. Paddle JJ. Evaluation of the haemoglobin colour scale and comparison with the HemoCue haemoglobin assay. Bulletin of the World Health Organization 2002;80:813-6.
3. Stott GJ, Lewis SM. A simple and reliable method for estimating haemoglobin. Bulletin of the World Health Organization 1995;73:369-73.
4. Van den Broek NR, Ntonya C, Mhango E and White SA. Diagnosing anaemia in pregnancy in rural clinics: assessing the potential of the Haemoglobin Colour Scale. Bulletin of the World Health Organization 1999;77:15-21.