Rhabdomyolysis CK Interpreter: How High Is Too High?
Rhabdomyolysis CK Interpreter: How High Is Too High?
Interpret a raised creatine kinase (CK) when rhabdomyolysis is the question. Enter the CK and your laboratory’s upper limit, the cause, the kidney function and the timing; the page gives the multiple of the upper limit against the five-times definition most studies use, explains why the CK alone does not predict kidney failure, and shows how much the cause matters, from the 2013 McMahon cohort of 2371 patients.
Is this CK rhabdomyolysis, and how worried should I be?
CK ÷ upper limit + cause + kidney → rhabdomyolysis and riskA 71-year-old man is found on the floor after a fall the previous day. CK 18,400 U/L (upper limit 200). Creatinine not yet back, urine normal colour.
What the CK can and cannot tell you
Above 5 × the upper limit (about 1000 U/L) → rhabdomyolysis, the definition most studies use
“Severe”: definitions range from 5000 to 15,000 U/L — no agreed line
Risk of death or dialysis depends on age, sex, cause, creatinine, calcium, phosphate and bicarbonate (McMahon 2013), not on the CK alone
- 5 × upper limit
- the rhabdomyolysis definition in most studies reviewed by Chavez et al (2016); ten times for statin-related cases
- time course
- CK rises over 12 hours, peaks at 3 to 5 days and returns to baseline 6 to 10 days later
- McMahon cohort
- 2371 adults with CK above 5000 U/L in two Boston hospitals, 2000 to 2011
Worked example
A 71-year-old man is found on the floor after a fall the previous day. CK 18,400 U/L (upper limit 200). Creatinine not yet back, urine normal colour.
Multiple = 18,400 ÷ 200 = 92 × the upper limit
Above 5 × → rhabdomyolysis
Above 5000 U/L → within the range where the McMahon cohort had 19% death or dialysis
Cause (immobilisation) is not in the lowest-risk group; kidney function unknown → creatinine, potassium, calcium, phosphate, bicarbonate now
Death or dialysis by cause (McMahon 2013)
| Cause | Death or renal replacement therapy |
|---|---|
| Cardiac arrest | 58.5% |
| Compartment syndrome | 41.2% |
| Sepsis | 39.3% |
| All causes | 19.0% |
| Seizures | 6.0% |
| Exercise | 3.2% |
| Myositis | 1.7% |
Why the CK number is not the risk
Creatine kinase leaks from damaged muscle, and a CK above five times the upper limit of normal — roughly 1000 U/L — is the definition of rhabdomyolysis used by most studies in the 2016 systematic review by Chavez and colleagues. The review also found no agreement on what makes it “severe”: definitions ranged from 5000 to 15,000 U/L. The time course matters as much as the level. CK rises over the first 12 hours, peaks at 3 to 5 days and returns to baseline in the following 6 to 10 days, so an early CK understates the injury and a late one can be normal after a serious episode. The creatine kinase unit converter converts units.
What readers usually want to know is whether the kidneys will fail, and the CK answers that poorly. The largest study, McMahon and colleagues in 2013, followed 2371 adults admitted with a CK above 5000 U/L: 19% died in hospital or needed renal replacement therapy. Risk depended heavily on the cause — 58.5% after cardiac arrest and 41.2% with compartment syndrome, against 3.2% after exercise and 1.7% with myositis — and on age, sex and the admission creatinine, calcium, phosphate and bicarbonate. Their score combined those eight variables, and in the validation cohort a score below 5 carried a 2.3% risk and a score above 10 a 61.2% risk. It is not reproduced on this page: its point table could not be checked against the published paper, and reproducing a points table from a calculator website would repeat any error in it.
In practice: interpret the CK against your own upper limit, repeat it, and put your effort into the kidney and the electrolytes. Hyperkalaemia is the early danger; acute kidney injury follows over days and should be staged with the KDIGO AKI stage calculator. Statin-related muscle symptoms have their own thresholds, in the statin muscle symptoms CK interpreter. This page supports, and does not replace, clinical judgement.
Frequently asked questions
What CK level is rhabdomyolysis?
Most studies define it as a CK above five times the upper limit of normal, roughly 1000 U/L. For statin-related cases the threshold used is ten times the upper limit.
What CK level causes kidney failure?
There is no single level. Definitions of severe rhabdomyolysis range from 5000 to 15,000 U/L, and in the McMahon study the risk of death or dialysis depended more on the cause, age, sex and the admission creatinine, calcium, phosphate and bicarbonate than on the CK.
When does CK peak after muscle injury?
It rises over the first 12 hours, peaks at 3 to 5 days and returns to baseline 6 to 10 days later. An early CK understates the injury; repeat it.
Why is the McMahon score not on this page?
Its point table could not be checked against the published paper, and copying it from a calculator website would repeat any error in it. The page uses the paper’s published outcome figures, which could be checked, instead.
Related calculators
References
- McMahon GM, Zeng X, Waikar SS. A risk prediction score for kidney failure or mortality in rhabdomyolysis. JAMA Intern Med. 2013;173(19):1821–1828. Figures from the abstract.
- Chavez LO, Leon M, Einav S, Varon J. Beyond muscle destruction: a systematic review of rhabdomyolysis for clinical practice. Crit Care. 2016;20(1):135.
- Stroes ES, Thompson PD, Corsini A, et al. Statin-associated muscle symptoms: impact on statin therapy — European Atherosclerosis Society Consensus Panel Statement. Eur Heart J. 2015;36(17):1012–1022.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.