Serum MB-creatine kinase is not elevated in active rheumatic carditis.

Total serum creatine kinase (CK) and the MB fraction of CK (CK-MB) activities were measured in 36 patients with active rheumatic carditis and on 33 controls. There were no significant differences in either the total CK or the CK-MB between the two groups. However, eight out of the 36 carditis patients had received intramuscular injections (IMI) prior to the assay: this sub-group showed a significant elevation of the total CK but not the CK-MB. Ten carditis patients (without prior IMI) had repeat assays done after their rheumatic activity had subsided: the mean total CK, but not the CK-MB, fell to levels below control values although these were not statistically significant. The results show that CK-MB is not of value in assessing activity in rheumatic carditis. Further, in assessing the significance of elevated total CK in any clinical situation, the influence of IMI and of bed rest should be taken into account.