Meta-analysis: Effects of glycerol administration on plasma volume, haemoglobin, and haematocrit

The use of glycerol in combination with excess fluid can be used to increase total body water. Because glycerol hyperhydration may also be misused to mask the effects of blood doping on doping-relevant parameters, namely haemoglobin and haematocrit, glycerol has been prohibited by the World Anti-Doping Agency since 2010. In order to test this rationale, the purpose of this meta-analysis was to quantify the effects of glycerol hyperhydration on plasma volume, haemoglobin, and haematocrit in comparison to administration of fluid only. Following a literature search, a total of seven studies was included and meta-analyses were performed separately for the effects on plasma volume (5 studies, total n = 54) and on haemoglobin (6 studies, n = 52) and haematocrit (6 studies, n = 52). The meta-analysis revealed that the increase in plasma volume was 3.3% larger (95%-CI: 1.1-5.5%) after glycerol administration when compared to fluid only. Reductions in haemoglobin were 0.2 g/dl (95%-CI: -0.3, 0.0) larger and there was no difference in the changes in haematocrit between glycerol and fluid administration (95%-CI: -0.7-0.8%). In comparison with other plasma-volume expanding agents, glycerol hyperhydration has a very limited potential in increasing plasma volume and altering doping-relevant blood parameters.