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Macro Creatine Kinase: Comparison of Different Screening Methods and Revision of the Bibliography

Pérez de Ciriza C and Nerea Varo

Introduction: Macro-creatine kinase (Macro-CK) is a complex with longer half-life that leads to elevation of enzyme activity and analytical errors. We present two cases with macro-CK to picture the problem. The aim of the study was to evaluate and compare different methods using polyethylene glycol (PEG) for screening.

Methods: Serum samples (n=39) were analysed using different PEG methods PEG6000, 30 minutes centrifugation, 3000 rpm, PEG8000, 10 minutes incubation and 5 minutes centrifugation, 1000 g Modified method 1, 10 minutes centrifugation. The recovery percentage and the polyethylene glycol precipitation activity (PPA) were calculated. In four patients macro-CK was confirmed by electrophoresis (Sebia).

Results: The recovery percentage was significantly higher in all non-macro-CK samples than in macro-CK (p<0.001) (Method 1: 80.6 ± 7.9%; (2): 60.2 ± 10.4% and (3): 79.9 ± 8.7% vs. Method 1: 13.8 ± 5.0%; (2): 12.4 ± 3.2% and (3): 8.7 ± 9.0%). No differences in recovery percentages were found between normal or elevated CK values. No differences were observed between methods 1 and 3 (p=0.453) and both were concordant (Confidence interval 95% was -8.819, 9.153). However, significant differences were observed between method 2 and the others (p<0.0001).

Conclusion: Method 3 is an adequate method for screening which would lead to a better identification of macro- CK interferences.