SERUM CREATINE-KINASE ACTIVITY IS NOT A RELIABLE MARKER FOR MUSCLE DAMAGE IN CONDITIONS ASSOCIATED WITH LOW EXTRACELLULAR GLUTATHIONE CONCENTRATION

Creatine kinase (CK, EC 2.7.3.2) assays usually contain thiol-reducing compounds to restore the enzyme activity. In this study, we investiga ted the effect of endogenous extracellular glutathione on serum CK act ivity. We examined CK activity and glutathione concentrations in serum from 200 healthy subjects (107 males, 93 females) and 38 patients wit h multiple organ failure, muscle wasting, and low serum CK activity (< 50 U/L) (24 males, 14 females). Muscle damage was further evaluated us ing serum myoglobin concentrations and aldolase activity. In the overa ll group, serum glutathione concentrations correlated with serum CK ac tivity (r = 0.791) but not with myoglobin concentrations and aldolase activity. In patients with multiple organ failure, low serum CK activi ties were accompanied by extremely low serum glutathione concentration s (<0.5 mu mol/L, P <0.001). Endogenous glutathione can be regarded as a CK-preserving agent during the lifetime of the enzyme in the circul ation (22 h on average). Serum CK activity should be interpreted with caution in patients with liver disease and multiple organ failure. In these conditions, the loss of CK activity due to extracellular glutath ione depletion cannot be restored by the presence of thiol-reducing co mpounds in the CK assays.