Abstract:

Objective To evaluate the ratio of creatine kinase MB isoenzyme（CK-MB） to creatine kinase（CK） for differentiating false increased results of CK-MB activity method in children. Methods Totally，304 samples with positive results of CK-MB activity method （higher than reference interval）were collected and randomized into a training set and a validation set by 1∶1. All the samples were determined by CK-MB mass assay. Positivity by mass assay was the standard of true positivity by active method. The clinical disease spectrum of children with false increased results of CK-MB activity method was analyzed. Receiver operating characteristic（ROC） curve analysis was used to evaluate the efficiency of CK-MB/CK in differentiating false increased results of CK-MB activity method. Results Among the 304 samples，141 cases of false positivity were determined by CK-MB activity method. The top 3 diseases were gastroenteritis（28 cases，19.9%），cardiovascular disease（27 cases，19.1%） and tumor（25 cases，17.7%）. In training set，the area under curve（AUC） of CK-MB/CK in differentiating true positive results of CK-MB activity method was 0.921 [95% confidence interval（CI）0.866-0.958，P<0.001]. Using 0.30 as CK-MB/CK cut-off value，the sensitivity of CK-MB/CK in differentiating true positive results of CK-MB activity method was 97.56%（95%CI 91.50%-99.70%）. In validation set，the AUC was 0.919（95%CI 0.862-0.956，P<0.001），and using 0.30 as CK-MB/CK cut-off value，the sensitivity was 97.53%（95%CI 91.40%-99.70%）. Conclusions CK-MB/CK can be used to determine the false increased results of CK-MB activity method. Gastroenteritis，cardiovascular disease and tumor children are prone to false positive results of CK-MB activity method. The positive results of CK-MB activity method in children with such diseases should be objectively judged according to clinical practice.

Key words: Creatine kinase MB isoenzyme, Mass assay, Activity method, False positivity