The body/venous haematocrit ratio and its use for calculating total blood volume from fractional volumes.

The measurement of body/venous haematocrit ratio has been assessed in 329 cases, in order to study the degree of error if the total blood volume were calculated from the red cell or plasma volume, using a pre-established correction factor. Three facts are clear from this study: (1) the ratio (correction factor f) is slightly lower than in the previous published data; (2) in polycythaemic and normal subjects, a low dispersion of the results around the mean value makes the potential error very low in all the cases; (3) in patients with an enlarged spleen, with anaemia and with dysproteinaemia, the large variation from case to case of the body/venous haematocrit ratio could cause large errors in determining total blood volume when using such a simplified method.