As part of a pig study to elucidate the interactions between low vitamin A status and helminth infections, surprisingly, we observed higher haemoglobin levels and packed cell volumes in the pigs with low vitamin A status. A possible haemoconcentration effect, due to some disturbance in the regulation of the extracellular fluid volume, could lead to underestimation of the prevalence of anaemia in vitamin A deficient human populations. Therefore, this phenomenon needs to be further clarified in studies involving determination of plasma volumes.