An exploratory study of hypnosis-induced blood count changes in chronically stressed individuals.

Hypnosis is a clinically accepted relaxation technique known for stress reduction. Results from hematological research provide evidence of changes in blood components through hypnosis. However, these hematological effects have been rarely examined. Hence, we exploratively investigated the effect of a single relaxation hypnosis on the hemogram in stressed individuals, assuming a reduction of leukocytes, thrombocytes, and erythrocytes (primary outcomes). Additionally, a reduction in the erythrocyte-related parameters (hemoglobin, hematocrit), and an increase in plasma volume was hypothesized (secondary outcomes). Forty-four either individuals (89 % women) with chronic stress and moderate to high hypnotic suggestibility were randomized to a hypnosis condition (20 min relaxation hypnosis; n = 20) or a control condition (20 min documentary; n = 24). Venous blood was drawn before and after the intervention and used to generate a differential hemogram and determine the plasma volume. The relaxation hypnosis led to a significant reduction in erythrocytes (Cohen's d=0.23) and consequently to a decrease in erythrocyte-related parameters (hemoglobin, d=0.27; hematocrit, d=0.37) as well as to a reduction in thrombocytes (d=0.15) in the hypnosis compared to the control condition. Putatively, this could be the consequence of an increased plasma volume (d=0.10), estimated by the hematocrit concentration and body weight. A hypnosis-induced change in leukocyte count could not be confirmed. Thus, a single session of relaxation hypnosis already alters specific blood count parameters. While relaxation-induced vasodilatation might explain these changes, it is still not completely clear how these changes affect our stress response system.