Raised Creatine Kinase (CK) Algorithm

Safety

Red Flags — Rhabdomyolysis & Necrotising Myopathy

Done

Express CK as a multiple of the upper limit of normal (ULN) — it varies between laboratories and between the sexes. The danger is rhabdomyolysis: muscle breakdown releasing myoglobin, which causes acute kidney injury and hyperkalaemia. Rhabdomyolysis is suspected when a raised CK occurs with compatible symptoms or precipitant, particularly muscle pain/swelling, weakness, dark urine, reduced urine output, AKI, hyperkalaemia or systemic illness. CK magnitude helps assess severity but does not replace clinical assessment.

CK ≥10× ULN or approximately ≥5,000 IU/L Treat as significant muscle injury/rhabdomyolysis until assessed. Urgent same-day medical assessment, particularly if symptomatic, dehydrated, after ongoing exertion/trauma, or if renal function, potassium or urine output is abnormal. Very high, rapidly rising or >50× ULN: urgent hospital/specialist assessment is generally appropriate, but the final disposition depends on renal function and trend, urine output, potassium, calcium and phosphate, fluid status, ongoing muscle injury, the precipitant, ability to maintain oral intake and obtain reliable follow-up, comorbidity and local protocol. Stop any causative drugs.

Any CK elevation with AKI, oliguria/anuria, hyperkalaemia, ECG changes, severe pain or weakness, dark urine, systemic illness, ongoing muscle injury or inability to maintain oral intake Immediate admission / emergency assessment. Urine dipstick positive for blood with few or no red cells supports pigmenturia and may reflect myoglobinuria, but is not diagnostic; dark urine is a red flag but is not specific — do not delay renal and electrolyte assessment or hospital referral while waiting for microscopy or urine myoglobin.

Objective progressive proximal weakness with substantially raised CK that persists or progresses despite stopping a statin Consider immune-mediated necrotising myopathy (e.g. anti-HMGCR) — rare but very significant. Needs urgent specialist (rheumatology/neurology) assessment; diagnosis usually includes myositis antibodies, EMG, MRI and/or muscle biopsy as appropriate. Muscle pain alone, or a CK that falls after stopping the statin, is more consistent with other statin-associated muscle syndromes.

Crush injury, prolonged immobility, seizures, extreme exertion or hyperthermia High rhabdomyolysis risk — check CK, renal function, potassium and urine; treat the precipitant; same-day assessment if CK ≥10× ULN, AKI or other red flags. CK may still be rising early after the injury.

New muscle aches or raised CK after starting / up-titrating a statin Go to the statin-intolerance pathway. Stop the statin for 4–6 weeks if CK is 4–10× ULN or symptoms are intolerable, then reassess (NHS England statin intolerance pathway).

Hyperkalaemia or AKI with a raised CK Any hyperkalaemia or a rising creatinine → same-day admission; severe hyperkalaemia or ECG changes → 999; treat as rhabdomyolysis until proven otherwise.

Tense, painful limb after crush, prolonged lie or injection-drug use Possible compartment syndrome — pain out of proportion, pain on passive stretch → emergency surgical assessment. Suspected compartment syndrome is a surgical emergency. Do not delay for CK, MRI or compartment-pressure testing if the clinical picture is convincing.

Chest pain with a raised CK CK also rises with myocardial injury — if the story is cardiac, manage as acute coronary syndrome (troponin, not CK, is the diagnostic test).

Weakness with breathing or swallowing difficulty Inflammatory myopathy or neuromuscular disease involving respiratory or bulbar muscles → same-day specialist assessment.

Creatine kinase is released from damaged skeletal (and cardiac) muscle. The clinical risk in a very high CK is rhabdomyolysis — myoglobin released from breaking-down muscle is filtered by the kidney and is directly nephrotoxic, precipitates in tubules, and (with the volume depletion that often accompanies the precipitant) causes acute kidney injury. Hyperkalaemia from muscle breakdown can be life-threatening independently. Because microscopy takes time, a positive dipstick for blood with few or no red cells supports pigmenturia (possible myoglobinuria) but is not diagnostic, and urine myoglobin can be transient — so you act on the clinical suspicion (dark urine + very high CK + a precipitant) without waiting. Immune-mediated necrotising myopathy is a rare but important mimic of simple statin myalgia: the key discriminator is objective, progressive proximal weakness with a substantially raised CK that persists or progresses after the statin is stopped, whereas ordinary statin myopathy improves on withdrawal. CK typically peaks one to three days after the muscle injury, so a moderately raised value early after a crush injury, prolonged lie or seizure may still be climbing — which is why a precipitant plus dark urine is acted on even before the number is very high.

Diagnose

When to check CK & how to interpret it

Done

When to check

Check CK if any significant symptoms: muscle pain, tenderness or weakness. This pathway also applies if CK is found raised for any other reason (incidental). New muscle symptoms on a statin → use the statin-intolerance pathway.

Express as multiples of ULN

CK reference ranges vary lab to lab and between the sexes — always interpret as a multiple of the local ULN, not the absolute number. An absolute value such as 500 IU/L can be more than 4× ULN in some laboratories, so do not use fixed absolute cut-offs; a CK of approximately ≥5,000 IU/L (about 30× a typical ULN) is often used as a practical rhabdomyolysis risk threshold, but the ≥10× ULN band is reached well below it — use 10× ULN, not 5,000 IU/L, to trigger same-day assessment.

Other tests at the same time

Check renal function, potassium and a urine dipstick; send microscopy/culture when infection or haematuria is part of the differential. In suspected significant rhabdomyolysis also check calcium, phosphate, bicarbonate/acid-base status, and an ECG if potassium is abnormal or the patient is unwell. Look actively for precipitating causes — especially drugs (statins/fibrates).

Confirm & recheck

A transient rise (e.g. after exercise) settles. If the patient is well, has no weakness, dark urine, oliguria, renal impairment or electrolyte disturbance, and recent strenuous exercise is a plausible explanation, avoid strenuous exercise for approximately 7 days and repeat CK. CK may normalise within several days after ordinary exertion, but extreme or eccentric exercise can cause a longer elevation. Do not delay hospital assessment in suspected rhabdomyolysis.

Recheck conditions

Ask the patient to avoid strenuous exercise, intramuscular injections and heavy alcohol for about a week before the repeat test, so that the result reflects the resting level.

Statins — before starting

If a person has persistent generalised unexplained muscle pain before a statin is started, measure CK; if it is more than 5× ULN, re-measure after 7 days; if still more than 5× ULN, do not start a statin; if raised but below 5× ULN, start statin treatment at a lower dose (NICE NG238, 2023, rec 1.5.7).

Statins — asymptomatic

Do not measure CK routinely in people taking a statin who have no muscle symptoms (NICE NG238).

Statins — new muscle symptoms

Assess severity, weakness, dark urine, renal function and other causes; check CK. Stop the statin for 4–6 weeks if CK is 4–10× ULN or symptoms are intolerable (CK >10× ULN: same-day assessment). If CK is <4× ULN, statin causality is less likely (but not excluded) — explore other causes, and if symptoms are tolerable consider continuing or rechallenging according to the local statin-intolerance pathway, using symptom response to a supervised pause/rechallenge to assess causality. Once symptoms resolve, reintroduce a lower dose or alternative statin where appropriate; seek specialist lipid advice if several statins are not tolerated (NICE NG238; NHS England statin intolerance pathway).

Unusual results

Isolated persistently raised CK with a normal examination may be macro-CK (a laboratory phenomenon) or idiopathic hyperCKaemia; the laboratory can advise on testing for macro-CK.

Because exercise is such a common and benign cause, a single mildly raised CK in a well person with a recent bout of exertion rarely needs a full myopathy work-up — the pragmatic step is to remove the precipitant (rest, hydration, hold any non-essential causative drug) and recheck after the muscle has recovered. Interpreting CK as a multiple of the ULN matters because reference ranges differ substantially between laboratories and are higher in men and in people of African ancestry, so an "absolute" number can mislead. The multiples used in this pathway follow a published phenotype classification for statin-related muscle toxicity (Alfirevic et al., Clinical Pharmacology and Therapeutics, 2014), adapted here as pragmatic triage bands.

Diagnose

Focused history & examination

Done

Symptom pattern

Pain vs weakness; distribution (proximal weakness — difficulty rising from a chair, climbing stairs, raising arms — suggests a myopathy); onset, duration, relation to exertion; dark urine; systemic features (rash, arthralgia, dysphagia).

Drug & substance history

Statins/fibrates and timing of any dose change; CYP3A4 interactors; antipsychotics, hydroxychloroquine, colchicine, retinoids, antiretrovirals; alcohol, cocaine, MDMA.

Precipitants

Recent unaccustomed/eccentric exercise, trauma, seizure, surgery, prolonged immobility, hyperthermia, intercurrent illness.

Background

Thyroid/endocrine symptoms; autoimmune features; family history of muscle disease; ethnicity (higher baseline CK in men and people of African ancestry).

Examination

Confirmed proximal weakness (e.g. unable to rise from squat), muscle tenderness/wasting, skin rash (dermatomyositis), thyroid status; check for signs of the precipitant.

Discriminating patterns

Exertional pain and cramps with dark urine after exercise, sometimes easing after a few minutes of rest ("second wind") → metabolic myopathy such as McArdle disease. Heliotrope rash, Gottron papules, shawl sign, mechanic's hands or objective proximal weakness → urgent rheumatology/dermatology assessment (?dermatomyositis); malignancy risk assessment and screening are coordinated through the specialist inflammatory-myopathy pathway and should include age-appropriate national screening — not an extensive GP cancer panel. Calf hypertrophy, family history, young male → muscular dystrophy. Weight gain, cold intolerance, slow relaxing reflexes → hypothyroid myopathy. Breathlessness, arthritis, mechanic's hands → antisynthetase syndrome.

Features of rhabdomyolysis

Muscle pain and swelling, weakness, dark urine, reduced urine output, and systemic upset (fever, nausea, confusion) — ask about all of these at the first contact.

Ideas and concerns

Patients on statins often worry the drug is "damaging their muscles"; asking about this early helps keep the conversation on the statin-intolerance pathway rather than permanent discontinuation.

The single most useful clinical discriminator is whether there is true weakness (especially proximal) as opposed to pain alone: ache after exertion or with a statin is usually benign, whereas progressive proximal weakness points towards an inflammatory or hereditary myopathy and changes the threshold for referral and investigation. A careful drug and exertion history identifies the reversible drivers that account for most raised CK results, so they can be removed before any extensive work-up. Pattern recognition matters because some myopathies have their own associations: dermatomyositis in adults carries an increased risk of an underlying cancer (screening coordinated by the specialist pathway), and antisynthetase syndrome brings interstitial lung disease, so these patients need specialist assessment rather than repeat CK checks.

Diagnose

Severity bands (multiples of ULN)

Done

Any CK + red flags

AKI, oliguria, hyperkalaemia, dark urine, severe pain/weakness or systemic illness → same-day hospital assessment/admission; stop causative drugs. 999 for shock, severe hyperkalaemia/ECG changes, compartment syndrome, altered consciousness or rapid deterioration — not for a CK value alone in a clinically stable patient.

≥10× ULN (or ≥5,000 IU/L)

Urgent same-day clinical assessment; consider rhabdomyolysis, especially with symptoms or ongoing injury. Stop causative drugs; on a statin → statin-intolerance pathway. Very high, rapidly rising or >50× ULN: urgent hospital/specialist assessment is generally appropriate — final disposition by the complete clinical picture and local protocol.

4–10× ULN, no red flags

More likely a secondary cause. Repeat CK and check renal function, potassium, urine and secondary causes (step 5); stop/review a causative drug where appropriate. CK 4–10× ULN with statin symptoms (or intolerable symptoms): stop the statin for 4–6 weeks; assess renal function, potassium, urine and symptoms; follow the statin-intolerance pathway.

<4× ULN, well

Usually incidental / transient (e.g. exercise). If recent strenuous exercise, normal examination and renal function: stop strenuous exercise, review drugs/precipitants, repeat CK after approximately 7 days.

Persistent + weakness / not falling

Persistent CK elevation with objective weakness, or CK not falling after stopping an implicated drug → urgent rheumatology/neurology assessment.

Persistent mild, asymptomatic

Individualised observation or non-urgent specialist advice; do not use an absolute <500 IU/L rule. The decision not to investigate further should be documented.

What overrides the band

Weakness, dark urine, AKI, hyperkalaemia or systemic illness move a patient up a band regardless of the number. Conversely, a very high CK in a fit athlete 24 hours after an ultra-endurance event, with normal renal function and clear urine, may need only close review — but that judgement belongs to the admitting team, not a phone call.

The degree of CK elevation guides both urgency and the breadth of investigation. Very high values are about preventing kidney injury (rhabdomyolysis); intermediate values prompt a structured search for a secondary cause; modest values in a well person are most often physiological and self-limiting. The bands are pragmatic multiples of ULN rather than fixed numbers because of inter-laboratory and sex variation. In the SCA, state the multiple explicitly ("your CK is about six times the top of the normal range") — it shows the examiner you are interpreting, not just reading, the result.

Diagnose

Causes & secondary work-up

Done

Physiological / muscle insult

Exercise (resistance or extreme) ± dehydration — commonest; trauma, seizures, recent surgery, systemic illness.

Substances

Alcohol excess (and associated thiamine deficiency); stimulants — cocaine, MDMA.

Drugs

Statins / fibrates (especially with other drugs affecting CYP3A4), antipsychotics, hydroxychloroquine, colchicine, systemic retinoids, antiretrovirals for HIV, some cancer drugs.

Endocrine

Thyroid disease, hyperparathyroidism, Cushing's, acromegaly.

Autoimmune

RA, SLE, coeliac disease, dermatomyositis, polymyositis. Commoner in those >50 with symptoms.

Hereditary myopathies

Glycogen storage disease (e.g. McArdle disease), muscular dystrophy, mitochondrial myopathy; carriers of Duchenne or Becker dystrophy (including some women) can have a raised CK with few symptoms.

Infection

Viral myositis (influenza, COVID-19 and others), especially in children with calf pain after a viral illness; severe sepsis.

Drug interactions to check

Simvastatin with clarithromycin or erythromycin, some azole antifungals and HIV protease inhibitors; dose limits for simvastatin with amlodipine, diltiazem, verapamil and amiodarone (MHRA Drug Safety Update, August 2012; SPC). Statin plus fibrate (especially gemfibrozil), fusidic acid, ciclosporin or colchicine raises the risk further. This list is non-exhaustive — check current MHRA advice, the SPC and your local formulary before prescribing.

Secondary investigations (persistent or unexplained)

Select according to the history and examination — not a routine package for every asymptomatic result. Commonly consider U&Es/eGFR Potassium Calcium Phosphate Magnesium Glucose LFTs TSH + urine testing. Add vitamin D, inflammatory markers, autoimmune tests, viral testing or other investigations only where clinically indicated.

Raised CK is frequently multifactorial — for example a statin plus alcohol plus a recent bout of unaccustomed exercise. The secondary panel screens for the common reversible drivers (thyroid and other endocrine disease, electrolyte abnormalities, renal impairment; vitamin D deficiency may contribute to myalgia or weakness but is not a standard explanation for every raised CK) so that the elevation is not wrongly attributed to a primary muscle disease. Persisting, unexplained elevation — particularly with weakness in someone over 50 — raises the possibility of an inflammatory myopathy, where rheumatology assessment and consideration of myositis-specific antibodies and imaging is worthwhile. Drug interactions deserve a specific check because the same statin dose can become myotoxic when a short course of a macrolide or azole blocks its metabolism — a common, preventable cause of statin-related rhabdomyolysis.

Treat

Management in primary care

Done

<4× ULN, well, recent exercise

Avoid strenuous exercise ~7 days, then repeat CK

Only if no weakness, dark urine, oliguria, renal impairment or electrolyte disturbance. Advise rest and good hydration; repeat CK after about 7 days (extreme or eccentric exercise can cause a longer elevation). Do not delay hospital assessment in suspected rhabdomyolysis. Review alcohol, medication and personal/family history of muscle disease.

Mild, stable, asymptomatic elevation

Individualised observation or non-urgent specialist advice

A mild, stable CK elevation with normal examination, normal renal function, no weakness, no relevant medication or systemic features, and a clear benign explanation may be observed after confirming the result at rest. Document the decision not to investigate further; do not base it on an absolute CK value (e.g. <500 IU/L) alone.

4–10× ULN, no red flags

Repeat CK + selected secondary tests

Check renal function, potassium and urine; stop/review a causative drug where appropriate; select secondary investigations (step 5) by history and examination. Treat any reversible cause found.

On a statin with muscle symptoms

Statin-intolerance pathway

Stop the statin for 4–6 weeks if CK is 4–10× ULN or symptoms are intolerable. If CK <4× ULN and symptoms tolerable: statin causality less likely — explore other causes and consider continuing or rechallenging per the local statin-intolerance pathway; re-challenge / switch per the lipids & statins pathway.

Statin re-challenge

For people with muscle symptoms on a statin, NICE NG238 (2023) advises stopping it and trying again when symptoms have resolved, to check whether the statin caused them; if symptoms recur, reduce the dose or change to a different statin; seek specialist lipid advice if several statins are not tolerated (see the local Management Pathway for Statin Intolerance in Cardiovascular Disease). Other lipid-lowering options (for example ezetimibe) are considered per NG238 and the relevant technology appraisals.

Vitamin D and coenzyme Q10

Correct vitamin D deficiency if found; coenzyme Q10 is not recommended as a treatment for statin muscle symptoms (clinical practice — trial evidence is inconsistent).

Communicating the evidence

Blinded N-of-1 trials have shown that most muscle symptoms reported on statins are similar on placebo (Herrett et al., BMJ, 2021) — a useful, non-dismissive point when discussing a re-challenge.

SCA phrasing

"Your muscle enzyme is mildly raised, which is very common after exercise. I'd like you to rest from hard exercise for a week and repeat the test. If your urine goes dark like cola, you pass much less urine, or your muscles become very painful or weak, please get seen the same day."

Next steps: see Acute kidney injury · Lipids · Hypothyroidism

Most management is conservative: remove the precipitant, hydrate, and recheck. The key judgement is distinguishing the well patient with a transient, exercise-related rise (who needs reassurance and a recheck) from the patient whose CK reflects a treatable secondary cause or an evolving myopathy. Statin-related symptoms have their own structured pathway because many patients tolerate a re-challenge, a lower dose or an alternative statin, and unnecessary permanent discontinuation removes important cardiovascular protection. The re-challenge sequence in NICE NG238 is designed to separate true statin myopathy from coincidental aches, which are common in the age group taking statins.

Refer

Referral

Done

Admit same day

Any CK with AKI, oliguria/anuria, hyperkalaemia, ECG changes, severe pain or weakness, dark urine, compartment-syndrome features, systemic illness, ongoing muscle injury or inability to maintain oral intake. Urgent same-day assessment for CK ≥10× ULN (or ≥5,000 IU/L); very high, rapidly rising or >50× ULN usually needs hospital/specialist assessment, decided on the whole clinical picture and local protocol. 999 for shock, severe hyperkalaemia/ECG changes, compartment syndrome, altered consciousness or rapid deterioration. Stop causative drugs.

Rheumatology

Suspected inflammatory myopathy — inflammatory or progressive weakness, persistent unexplained elevation, or CK not falling after stopping an implicated drug, especially in those >50 with symptoms.

Neurology

Neurology/metabolic clinic: suspected hereditary myopathy (e.g. young patient, family history, exertional symptoms, recurrent rhabdomyolysis) or unexplained progressive weakness.

Lipid clinic

Persistent statin intolerance (several statins not tolerated).

Renal / acute medicine

Rhabdomyolysis or AKI.

Surgical emergency

Suspected compartment syndrome — do not delay for CK, MRI or compartment-pressure testing if the clinical picture is convincing.

Statin pathway

New muscle aches or raised CK on starting/up-titrating a statin → lipids & statins (statin-intolerance) pathway.

Urgency

Same-day: weakness with breathing or swallowing difficulty (step 1). Urgent (days): progressive proximal weakness, rash of dermatomyositis, weakness persisting after stopping a statin. Specialist assessment: persistent unexplained CK elevation on repeat testing, particularly with objective weakness or abnormal examination. Also consider referral for progressive elevation, abnormal neurological examination, family history, recurrent exertional rhabdomyolysis, persistent elevation after stopping a suspected medicine, or a suspected hereditary cause in a well patient.

What to include

Serial CK values with dates and the local ULN, exercise and drug history (with statin dates), renal function, urine results, secondary investigation results, examination findings including a clear statement on weakness, and family history.

Occupational and sport

Athletes, military recruits and manual workers with recurrent exertional rhabdomyolysis need specialist assessment for an underlying metabolic myopathy before returning to full training.

Referral is reserved for the minority: those with a persistently unexplained or rising CK, with weakness suggesting an inflammatory or hereditary myopathy, where specialist investigation (antibodies, EMG, MRI, muscle biopsy or genetic testing) changes management. Most raised CK results are explained by a reversible cause found in primary care. A well-documented referral — serial values expressed as multiples of ULN, dated drug changes and an explicit strength examination — speeds up specialist triage considerably.

Lifestyle

Modifiable Factors — Remove the Muscle Insult

Done

Rest & hydrate Avoid intense/eccentric exercise and stay well hydrated before rechecking — exercise is the commonest cause; repeat CK after about 7 days. Advise a gradual return once CK normalises.

Alcohol & stimulants Reduce alcohol (and address thiamine deficiency); avoid cocaine/MDMA.

Review drugs Reassess statins/fibrates and CYP3A4-interacting drugs; use the statin-intolerance pathway rather than abandoning cardiovascular protection.

Treat reversible causes Correct thyroid disease and vitamin D deficiency if found; manage other endocrine/electrolyte abnormalities found on the secondary panel.

Training sensibly Build up new or eccentric exercise gradually (e.g. spin classes, heavy lifting), stay hydrated, and avoid training in extreme heat or when unwell.

Supplements Some bodybuilding and weight-loss supplements contain stimulants or undeclared drugs — ask directly and advise stopping while CK is raised.

Because raised CK is usually multifactorial, the highest-yield intervention is simply removing the stacked muscle insults — recent unaccustomed exercise, alcohol, dehydration and a contributing drug — and then re-measuring once the muscle has recovered. Treating an under-recognised hypothyroidism can normalise a persistently raised CK without any need for myopathy investigation. Advice about graded return to exercise matters because exertional rhabdomyolysis tends to occur in people who are unaccustomed to a new, intense activity rather than in the habitually fit.

Follow-up

Monitoring & Safety-net

Done

Recheck

Repeat CK after about 7 days without strenuous exercise if well. A mild, stable elevation with normal examination and a clear benign explanation may be observed — document the decision; no absolute CK cut-off (e.g. <500 IU/L).

If still raised

Persistent unexplained elevation → complete the secondary-cause panel ± rheumatology/neurology referral. Track the trend, not a single value.

Same-day / 999

Dark (cola/tea-coloured) urine, reduced urine output, severe muscle pain or weakness — possible rhabdomyolysis with AKI: same-day hospital assessment. Stop causative drugs. 999 for collapse, confusion, rapid deterioration, or a tense, swollen, very painful limb (possible compartment syndrome).

Progressive weakness

Weakness that worsens despite stopping a statin → urgent specialist review for immune-mediated necrotising myopathy (myositis antibodies, EMG, MRI and/or biopsy as appropriate).

After rhabdomyolysis

Check renal function has recovered after discharge; record the episode and any culprit drug in the notes; advise on the precipitant (drug, exertion, alcohol); refer if recurrent or unexplained.

Document

Record the CK as a multiple of ULN, the precipitant, drug changes made, the recheck date and the safety-net given.

Rhabdomyolysis can evolve after the initial test, so a patient sent home with a moderately raised CK must know the warning features — severe pain, dark urine, reduced urine output — that mandate urgent reassessment. Following the trend rather than a single number distinguishes the transient, resolving rise from the persistent elevation that warrants a full work-up, and the progressive-weakness rule is the safety-net for the rare necrotising myositis that does not improve on statin withdrawal. A clear recheck date, handed to the patient, stops a mildly raised CK from being forgotten in the results inbox.