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Arthritis and Rheumatism

Interpretation Creatinine Blood Test

10/10/2008

Question:

My creatinine kinase blood test came in at 24 vs normal range of 25-287, while other tests were normal.  What does this mean? Tests were taken because my muscles, particularly my shoulders, ache. I take 40 mg of zocor with 1000 grams of slonician for cholesterol. I am 76 in excellent shape-159 lbs 5`9" and work out regularly. Past angina, got stent 12 yrs ago and pacemaker last year for periodic syncope problem that was undiagnosed for 30 yrs (skipped heart beats). Thanks.

Answer:

Creatinine kinase (CK), also known as creatinine phosphokinase (CPK), is an enzyme found in the heart, brain, and skeletal muscle. Its clinical utility is typically to raise suspicion of injury to the heart or skeletal muscle if the CK level is elevated. Screening for a low CK is not a typical clinical use.

The most well-known cause of a low CK is reduced muscle mass related to disuse, low physical activity, poor nutrition, or aging. It is hypothesized that certain conditions such as Cushing's Disease or steroid therapy may decrease the amount of CK enzyme that reaches the serum. Other obscure associations with low CK have been noted.

My suspicion is that your low CK does not have high clinical significance; however, your physician may advise you differently. Also of note, the normal ranges for labs have different thresholds for sensitivity to detect "normal" values. In other words, depending on the type of lab, the normal range may only capture 95% (or some other prespecified value) of the "normal" population, leaving 5% of the "normal" population outside of the lab normal value range.

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Response by:

Raymond  Hong, MD, MBA, FACR Raymond Hong, MD, MBA, FACR
Formerly, Assistant Professor of Medicine
School of Medicine
Case Western Reserve University