Background and objectives: Analysis of haemoglobin (Hb) dilution after bleeding is a simple, inexpensive and non-invasive method to estimate blood loss. Blood volume is estimated, taking sex, weight and height into account. The Hb concentration before and after blood loss is analysed and, from the difference, the blood loss volume can be calculated assuming a normovolemic subject. Although widely used this method has never been validated.
Material and methods: The Hb concentration of 21 blood donors was analysed before and up to 4 days after a standard blood donation and in another 18 blood donors the Hb concentration was analysed before and on day 4, 6, 8, 11 and 14 after blood donation. The blood volume of each donor was calculated and the donated blood volume was estimated by weighing. We calculated the blood loss by the Hb dilution method and compared the calculated value with the donated blood volume.
Results: The mean donated blood volume was 442 +/- 10 ml, whereas the mean calculated blood loss was 152 +/- 214 ml using the Hb concentration of the first day after donation and 301 +/- 145 ml with the Hb concentration of day 6 after blood donation after which no further Hb decrease was observed. The directly measured Hb concentration was always higher than the calculated/expected Hb concentration based on the blood donation volume.
Conclusions: The Hb dilution method underestimates the true blood loss by more than 30% after a moderate blood loss of approximately 10% of the total blood volume.