In vitro diagnosis of susceptibility to malignant hyperthermia: evaluation of tests with halothane-caffeine, potassium chloride, suxamethonium and caffeine-suxamethonium.

Susceptibility to MH was determined in 77 patients according to the protocol of the European MH Group. Additional muscle bundles were used for diagnostic in vitro tests with caffeine in the presence of 1% halothane, potassium chloride, suxamethonium, and caffeine-suxamethonium. Significant differences between MH-susceptible (MHS) and MH-negative (MHN) patients were obtained with the halothane-caffeine test and the potassium chloride test, whereas no differences were found with the suxamethonium test. In the test with caffeine-suxamethonium, a different response to caffeine but not to suxamethonium was obtained. In all tests there was an overlap in results between MHS and MHN groups, and the predictive values of the tests ranged between 63 and 95%. Prior small doses of caffeine followed by a 4 mmol/l dose of caffeine elicited significantly smaller contractures than 4 mmol/l given as the first dose of caffeine. This underlines the necessity of a common protocol for performance and interpretation of diagnostic tests for MH.