Creatine Kinase - CK

What is CK?

CK is an enzyme which is found in muscle. It is involved in ATP production required for muscle contraction. There is normal 'leakage' of CK from cells into plasma.

The amount of CK detected in blood will depend on the muscle mass of the person (and also on ethnicity) so that the reference ranges are an average only.

Why measure CK?

Muscle damage will result in the release of CK into the circulation. This will occur whether it is heart muscle eg myocardial infarction, skeletal muscle eg rhabdomyolysis or smooth muscle eg gut infarction.

What do the results mean?

This depends on the clinical scenario

1. Patient complains of chest pain

The best current marker for myocardial damage is Troponin due to its cardiac specificity. If a patient is found collapsed on the floor and the CK result is high, this could be due to a heart attack and/or skeletal muscle damage.

2. Patient on a statin complains of generalised muscle aches

Statins may cause muscle problems in about 1 in 1000 patients. The reasons for this are not fully understood but could in part be due to CoQ10 deficiency or farnesyl pyrophosphate deficiency due to inhibition of HMG-CoA Reductase in the metabolic pathway by the statin . Muscle aching without a rise in CK is termed myalgia. Muscle aching with a rise in CK is myositis which with high CK levels is termed rhabdomyolysis.

The decision as to whether to stop the statin depends on

(i) The level of CK. A baseline CK prior to statin treatment is very useful to compare with. A rise in CK above 5 x ULN should be considered significant and the statin stopped.

(ii) The nature of the CVD risk being treated ie risk of continuing statin vs risk of stopping statin

(iii) How the patient feels

Untreated hypothyroidism increases the risk of muscle problems when on a statin and TFT should be checked prior to statin therapy.

Discuss with Dr Rob Lord if in doubt.

3. Elevated CK, cause not apparent

Assuming not due to statin treatment then the type of CK in the circulation needs to be determined. CK exists in 3 dimeric forms - CKMM, CKMB and CKBB. In addition it can also exist complexed to immunoglobulins to give a macroCK which is cleared more slowly from the circulation. These different forms can be detected if required using isoenzyme analysis.

Discuss with Dr Rob Lord regarding further investigation.