Detection of carriers for Duchenne muscular dystrophy. Quality control of creatine kinase assay.

A report by Bullock and coworkers has emphasized the need for standardization of the CK assay in carrier detection for DMD. A collaborative study, according to a well-specified design and involving two laboratories in Paris and Lyon, indicates that the reliability of this assay can be improved provided that special attention is paid to information about participating subjects, laboratory protocol, and repeated sampling. On a random sample of young women, mean and variance of ln(CK) are 1.66 and 0.015 respectively. Within and between variance components are in a 3:4 ratio, homogeneous between populations. Additional use of a common test serum should insure good reliability of this assay among laboratories.