Reasoning GP · Algorithm · 1-page summary
Raised creatine kinase (CK)
For: a raised CK in primary care, with muscle symptoms or found incidentally, including on a statin. Not for: chest pain with a cardiac story (troponin, not CK — chest pain algorithm); statin choice and targets (hypercholesterolaemia protocol).
Core rule: read CK as a multiple of the local upper limit of normal (ULN). Rhabdomyolysis is a clinical diagnosis, not a CK number: dark urine, low urine output, AKI or hyperkalaemia move the patient up a band whatever the value.
0Stop — call 999 now — any CK value
- Shock, severe hyperkalaemia or ECG changes, altered consciousness or rapid deterioration → 999
- Tense, painful limb after crush, prolonged lie or injection-drug use; pain out of proportion or on passive stretch (compartment syndrome) → 999 surgical emergency. Do not wait for CK, MRI or pressure testing.
- While waiting: stop any causative drug. Do not delay transfer for urine microscopy or urine myoglobin. 999 is not for a CK value alone in a clinically stable patient.
1Triage by multiple of ULN — red flags override the band
| CK | Action |
|---|---|
| Any + red flag | AKI, oliguria, hyperkalaemia, ECG change, dark urine, severe pain or weakness, systemic illness, ongoing injury, poor oral intake → Same-day hospital |
| ≥10× ULN | (or ≥5,000 IU/L) Rhabdomyolysis until assessed → Same-day assessment; >50× or rising → usually hospital |
| 4–10×, well | Secondary cause likely: repeat CK, selected tests; review drugs |
| <4×, well | Usually exercise: no strenuous exercise, repeat CK at ~7 days |
| Persistent | With objective weakness, or not falling after stopping a drug → Urgent rheumatology / neurology |
2Screen — one row is enough
- Crush, long lie, seizure, extreme exertion, hyperthermia: CK may still be rising → Same-day if ≥10× ULN, AKI or red flag.
- Any hyperkalaemia or rising creatinine with raised CK → Same-day admission
- Weakness with breathing or swallowing difficulty → Same-day specialist
- Progressive proximal weakness, CK persisting or rising after stopping a statin (?immune-mediated necrotising myopathy) → Urgent specialist
- Heliotrope rash, Gottron papules, shawl sign, mechanic's hands (?dermatomyositis) → Urgent rheumatology / dermatology
- Chest pain, cardiac story: manage as ACS → chest pain algorithm.
3Assess — once blocks 0–2 are answered
☐ CK as a multiple of ULN ☐ renal function, K⁺, urine dipstick ☐ significant rhabdomyolysis: calcium, phosphate, bicarbonate; ECG if K⁺ abnormal or unwell ☐ statin/fibrate dates, CYP3A4 interactors, alcohol, cocaine, MDMA, supplements, exertion ☐ proximal power (rise from squat), rash, thyroid
Dipstick blood with few red cells supports pigmenturia; not diagnostic. No routine CK on a statin without muscle symptoms.
4Classify — only if the screen is negative
- Exercise — unaccustomed or eccentric exertion, well, commonest → rest, repeat CK.
- Drug — statin/fibrate (simvastatin + clarithromycin or azoles), antipsychotics, colchicine, retinoids → stop or review.
- Endocrine — hypothyroid (weight gain, cold intolerance, slow-relaxing reflexes) → TSH, treat.
- Inflammatory myopathy — objective proximal weakness, rash; commoner >50 with symptoms → rheumatology.
- Hereditary or metabolic — exertional cramps with dark urine, "second wind" (McArdle); calf hypertrophy, family history → neurology.
- Uncertain — isolated, normal examination: consider macro-CK (ask the lab) or idiopathic; track the trend, document.
5Treat today — only these
- Statin with muscle symptoms: CK 4–10× ULN or intolerable → stop for 4–6 weeks, then rechallenge. CK <4× and tolerable → look for other causes; consider continuing or rechallenging (NHS England statin intolerance pathway).
- Before a statin, persistent unexplained muscle pain: CK >5× ULN → repeat at 7 days; still >5× → do not start; raised but <5× → start at a lower dose (NG238).
- Remove the insult: rest, hydrate, cut alcohol, stop stimulants. No strenuous exercise, IM injections or heavy alcohol for ~1 week before the repeat.
6Refer routinely
- Persistent unexplained elevation on repeat testing → rheumatology. Young, family history, exertional symptoms, recurrent rhabdomyolysis → neurology/metabolic clinic.
- Several statins not tolerated → lipid clinic. Send serial CK with dates and ULN, and a clear statement on weakness.
7Never reassure by
- An absolute cut-off such as CK <500 IU/L.
- A CK below 5,000 IU/L when it is already ≥10× ULN.
- A moderate CK early after a crush, long lie or seizure — it may still be rising.
- Waiting for urine microscopy or myoglobin.
- "Statin aches" when weakness progresses after stopping.
- A fit athlete with a very high CK assessed by phone.
8Safety-net — say it, then document it
999 “Collapse, confusion, getting rapidly worse, or a tense, swollen, very painful limb — call 999.” Same day: “If your urine goes dark like cola, you pass much less urine, or your muscles become very painful or weak — get seen the same day.” Weakness worsening after stopping a statin → urgent review.
Remote or OOH: a very high CK is never judged safe by phone, even in a fit athlete — that judgement belongs to the admitting team.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
CK <10× ULN; renal function, K⁺ and urine normal
Cause named (exercise, drug) or uncertainty stated
Repeat CK date and owner set; drug changes recorded
Safety-net given and documented
Summary of the full Reasoning GP raised CK algorithm, which holds the detail, causes, statin pathway and evidence. Sources: NICE NG238; MHRA Drug Safety Update (simvastatin, August 2012); local statin-intolerance pathway (local guidance); Alfirevic et al. 2014. Clinical reference — interpret against your local laboratory range, follow local policies and check doses and interactions in the current BNF.