Effects of pre-donation salt-loading on the occurrence of delayed vasovagal reactions

Vasovagal reaction (VVR) is the most frequent adverse reaction in blood donation, which usually recovers soon without complications. However, syncopal VVR can result in severe injury due to a fall. Some reports have shown the possibility to prevent VVR with salt-loading prior to blood donation. This semi-randomized controlled study aims to clarify the preventive effect of salt-loading on VVR among whole blood (WB) donors.

During the study period, donors who donated 400 mL of WB on odd days were assigned to the salt-loading group and those who donated on even days to the control group. Participants in the salt-loading group were asked to take three tablets containing 0.3 g salt in total.

The incidence of VVRs occurring >20 min after needle removal (delayed VVR [dVVR]) did not significantly differ between the two groups. Secondary analysis suggested a possible dose-dependent preventive effect against dVVR (odds ratio [OR]: 0.70; 95% confidence interval [CI]: 0.52-0.94; p = 0.02). The number of delayed syncopal VVR episodes in summer was lower in the salt-loading group than in the control group (n = 1 vs. 8; OR: 0.13; p = 0.04; pre-specified α = 0.0125).

There was no significant preventive effect of pre-donation salt-loading on VVR. Further investigations with sufficient number of participants are needed to conclude the suggested dose dependency and seasonal preventive effect on dVVRs.