[Diagnosis of anemia at high altitude: problems encountered in Tibet]

To test the hypothesis that Tibetans do not increase their haemoglobin concentration with increasing altitude, haemoglobin concentrations of children aged 6 to 72 months were analyzed. The mean haemoglobin concentrations in the different age groups are significantly lower than the mean concentrations expected at this altitude. Histograms and tests for normality show that the haemoglobin distributions are Gaussian. The probability plots confirm the coefficients of skewness, which indicate a superimposed subpopulation towards the lower range of haemoglobin values. A mixed distribution analysis identifies that the curvilinear deviation found in the probability plot encompasses 10 to 12% of the studied population. Together with the normality of the haemoglobin distributions, we are led to suppose that this is the anaemic population. These figures are considerably lower than those found using recommended cut-off values for this altitude; 40 and 46%. Two possible explanations are put forward: 1) the whole population is submitted to the same factor and hence the whole population should be considered anaemic, 2) Tibetans react differently to altitude than other mountain people and have adapted themselves without increase in haemoglobin.