Interpretation of creatine kinase and aldolase for statin-induced myopathy: Reliance on serial testing based on biological variation.
BACKGROUND
Statins are widely used drugs to reduce LDL cholesterol and risk for cardiovascular disease. Varying degrees of myopathies occur with statin use, ranging from mild myalgic symptoms alone to documented muscle damage and rhabdomyolysis. The activity of creatine kinase (CK) above a population-based reference range has been used to differentiate myalgias from documented myositic injury due to statins. However, because normal ranges for CK depend on gender, exercise, and ethnicity and are necessarily broad, it is possible for a patient to have myositic injury with a result that is within the reference range. Therefore, serial testing relative to baseline levels may be more effective in detecting mild increases in CK.


METHODS
To properly interpret results of serial testing, we determined the biologic variation of CK and aldolase, another enzyme released from muscle, from biweekly blood collections for 8 weeks from 17 healthy subjects.


RESULTS
Using log transformation, we calculated a reference change value of about +140% and -60% for both CK and aldolase.


CONCLUSIONS
The use of calculated RCV could help to improve the detection of those statin side effects promoting variation in CK values, which must be determined in clinical studies. The clinical significance of detecting more cases of statin-induced myopathy must also be examined.
Department of Laboratory Medicine, University of California, San Francisco, CA, USA.
Alan H B
AH
Wu
Andrew
A
Smith
Frank
F
Wians
D000328:Adult; D000465:Algorithms; D000924:Anticholesteremic Agents / Q000009:adverse effects* / Q000494:pharmacology; D004796:Clinical Enzyme Tests / Q000379:methods* / Q000592:standards; D003402:Creatine Kinase / Q000097:blood*; D003404:Creatinine / Q000097:blood; D005260:Female; D005634:Fructose-Bisphosphate Aldolase / Q000097:blood*; D005919:Glomerular Filtration Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009135:Muscular Diseases / Q000097:blood / Q000139:chemically induced* / Q000175:diagnosis* / Q000473:pathology; D020097:Natriuretic Peptide, Brain / Q000097:blood; D012016:Reference Values; D019821:Simvastatin / Q000009:adverse effects* / Q000494:pharmacology; D013997:Time Factors
D000924:Anticholesteremic Agents; D020097:Natriuretic Peptide, Brain; D019821:Simvastatin; D003404:Creatinine; D003402:Creatine Kinase; D005634:Fructose-Bisphosphate Aldolase