Factitiously Low Total Creatine Kinase Activity in Severe Rhabdomyolysis: A Case Series.

Factitiously low total creatine kinase (CK) activity can occur in severe rhabdomyolysis, potentially causing misdiagnosis and inappropriate patient management. We hereby describe 2 cases of severe rhabdomyolysis with falsely low total CK activity. Case 1 was a 61-year-old lady with underlying diabetes mellitus diagnosed with severe rhabdomyolysis secondary to severe pneumonia. Case 2 was a 77-year-old man with underlying diabetes mellitus diagnosed with severe rhabdomyolysis secondary to recurrent pyogenic spondylodiscitis. Both cases showed unexpectedly low total CK activity (<7 U/l N: 26-192 U/l). Post-dilution procedures showed markedly elevated total CK activity for case 1 (18,364 U/l [1:11]) and case 2 (15,217 U/l [1:11]). Unfortunately, both patients succumbed despite optimized medical treatment due to multi-organ failures. Measurement of CK in blood is considered as a diagnostic marker for rhabdomyolysis and its severity. Most of the laboratory nowadays measures total CK activity using enzymatic coupled with spectrophotometry method. However, substrate depletion can occur in severe rhabdomyolysis in which creatine phosphate is consumed by high concentration of CK in sample before the kinetic measurement is initiated, leading to factitiously low total CK activity. Sample dilution can be done to obtain the accurate total CK activity, avoiding result reporting error and possibility misdiagnosis of rhabdomyolysis. Good communication between clinical and laboratory personnel is vital to prevent the error and safeguard patient management.