From the Guidelines
When evaluating statin myopathy, the most important laboratory test is creatine kinase (CK), which measures muscle damage, and it is recommended to measure CK levels in individuals with severe statin-associated muscle symptoms or objective muscle weakness, as stated in the 2019 guideline 1. The evaluation of statin myopathy should also include liver function tests (ALT, AST), kidney function tests (creatinine, BUN), thyroid function (TSH), and vitamin D levels.
- A complete metabolic panel and complete blood count are also recommended to help distinguish between true statin-induced myopathy and other conditions that may cause similar symptoms.
- If CK is significantly elevated (typically >5-10 times the upper limit of normal) with muscle symptoms, the statin should be temporarily discontinued, as recommended in the 2019 guideline 1.
- For persistent or severe cases, consider checking inflammatory markers like ESR and CRP, and in selected cases, aldolase or myoglobin levels.
- Testing for genetic variants like SLCO1B1 may be helpful in some patients to assess risk for statin-induced myopathy, as mentioned in the example answer.
- Electrolytes including potassium, calcium, and magnesium should be checked as imbalances can worsen muscle symptoms. These tests help distinguish between true statin-induced myopathy and other conditions that may cause similar symptoms, allowing for appropriate management decisions regarding statin therapy continuation, dose adjustment, or switching to an alternative medication, as recommended in the 2019 guideline 1. The 2019 guideline 1 also recommends that routine measurements of creatine kinase and transaminase levels are not useful in patients treated with statins, unless they have severe statin-associated muscle symptoms or objective muscle weakness.
From the Research
Labs to Check with Statin Myopathy
To diagnose and manage statin myopathy, several laboratory tests can be useful:
- Creatine kinase (CK) levels: Elevated CK levels can indicate muscle damage, but normal CK levels do not rule out myopathy 2
- CK-MB (myocardial band) isoenzyme: Elevated CK-MB levels may be associated with statin-associated muscle symptoms (SAMS) 3
- Troponin: May be elevated in cases of rhabdomyolysis, a severe form of myopathy 4
- Carbonic anhydrase type III: May be a biomarker of muscle damage, but its utility in diagnosing statin myopathy is not well established 3
- Liver function tests: To monitor for potential liver damage, as statins can cause elevations in liver enzymes 5, 6
- Renal function tests: To monitor for potential kidney damage, as rhabdomyolysis can cause acute renal failure 4
Patient Evaluation
When evaluating a patient with suspected statin myopathy, consider the following:
- Medical history: Presence of conditions such as hypothyroidism, diabetes mellitus, or hepatic or renal disease, which may increase the risk of myopathy 5, 6
- Medication history: Use of other medications that may interact with statins and increase the risk of myopathy, such as cytochrome P-450 3A4 inhibitors or gemfibrozil 5
- Physical examination: To assess for muscle weakness or tenderness 2
- Symptom severity: To determine the need for statin discontinuation or dose reduction 5, 6