Blood Tests for Muscle Cramps: What to Check

Muscle cramps are sudden, painful tightenings of a muscle, most often in the calf and often at night. The NHS describes them as common and usually harmless, and many have no clear cause. They become more likely with age, hard exercise, later pregnancy, dehydration and some medicines, including statins and diuretics.

When cramps are frequent, keep waking you, or come with weakness or aching, a blood test can check for treatable causes such as low magnesium, calcium or potassium, kidney or thyroid problems, raised blood sugar or muscle irritation from statins. This guide explains each test, which panel to choose and the warning signs that need urgent care.

Test it in Chiswick: our Muscle and Joint Screen blood test costs £129, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Prefer to test at home? A home finger-prick kit is also available, ask us when you enquire.

Quick answer

The main blood tests for muscle cramps are magnesium, calcium, potassium and sodium, kidney function, vitamin D, creatine kinase (CK), thyroid function (TSH) and HbA1c. Low magnesium, calcium and potassium can all cause cramps, an underactive thyroid can cause aches and cramps, and kidney disease and diabetes-related nerve damage are other causes. If you take a statin and have unexplained muscle pain, a CK test shows whether muscles are inflamed. Severe muscle pain with dark urine needs A&E straight away.

Blood tests that can help

Magnesium

NHS pharmacy guidance lists muscle cramps, tiredness and weakness among the symptoms of mild low magnesium. Low magnesium often occurs alongside low potassium and can make low potassium harder to correct. A Magnesium test costs £39. Read more in our guide to magnesium levels.

Calcium

Low calcium can cause muscle cramps, twitching and tingling around the mouth or in the fingers. Calcium is controlled by parathyroid hormone and vitamin D, and the result is adjusted for the protein albumin. Our Adjusted Calcium test costs £49. See our guide to calcium levels.

Potassium and sodium

Low potassium can cause muscle weakness, cramps and tiredness. Common causes include diarrhoea, vomiting and water tablets (diuretics). Sodium is checked alongside it, because salt and fluid balance is affected by dehydration and some medicines. You can test Potassium (£49) or Sodium (£49) alone, but the Kidney and Electrolytes (U&E) test checks both plus kidney function for the same £49.

Kidney function

The NHS lists muscle cramps among the symptoms of more advanced chronic kidney disease, which is diagnosed with blood and urine tests. Kidney function also affects your potassium, calcium and magnesium levels. The Kidney and Electrolytes (U&E) test (£49) measures creatinine, eGFR, urea, sodium, potassium and chloride. Our kidney results guide explains eGFR.

Vitamin D

Vitamin D helps keep bones and muscles healthy and helps regulate the amount of calcium in the body. Long-term deficiency can cause bone pain from a condition called osteomalacia. A Vitamin D test costs £59. NHS advice is to consider 10 micrograms a day in autumn and winter.

Creatine kinase (CK) and statins

CK is released into the blood when muscles are inflamed or damaged. Statins can sometimes cause muscle inflammation, and the NHS advises speaking to your doctor if you have muscle pain, tenderness or weakness that cannot be explained. A big rise in CK may mean your doctor pauses or changes your statin. Hard exercise can also raise CK, so mention any recent training. Our Creatine Kinase (CK) test costs £49. Do not stop a prescribed statin without talking to your doctor first.

Thyroid function

The British Thyroid Foundation lists muscle weakness, cramps and aches among the most common symptoms of an underactive thyroid, along with tiredness, feeling cold and weight gain. A TSH test costs £39, or the full Thyroid test with free T3, free T4 and antibodies costs £59.

HbA1c (blood sugar)

Diabetes is the most common cause of peripheral neuropathy (nerve damage) in the UK, and the NHS lists twitching and muscle cramps among its symptoms. An HbA1c test (£59) shows your average blood sugar over the past two to three months. See our guide to HbA1c levels.

Which test should I book?

• A focused start: Muscle and Joint Check, £59. CK, LDH, uric acid and rheumatoid factor, a quick look at muscle irritation, gout and inflammatory joint disease.
• A broader picture: Vitamins and Minerals Check, £99. Magnesium, adjusted calcium, vitamin D, iron studies with ferritin, B12, folate and zinc, suited to cramps with tiredness or a restrictive diet.
• The fullest view: Muscle and Joint Screen, £129. Kidney function and electrolytes, calcium, magnesium, vitamin D, CK, liver function, iron, CRP and immune markers in one sample.

If you also want thyroid function or HbA1c, add a TSH or HbA1c test at the same visit.

What blood tests cannot tell you

Most people with cramps have normal blood tests, because many cramps are linked to age, muscle fatigue or posture rather than a measurable imbalance. Blood tests also cannot assess nerve compression in the back, poor circulation or problems with the muscles themselves. A single result shows one moment in time, so a borderline level may need repeating.

If your results are normal, regular calf stretches, staying well hydrated and reviewing your medicines with your GP or pharmacist are good next steps.

When to see a GP urgently

Go to A&E or call 999 if you have severe muscle pain or weakness together with dark brown, red or cola-coloured urine. This can be a sign of rhabdomyolysis, a rare but serious breakdown of muscle that releases CK and myoglobin into the blood and can damage the kidneys. It can follow very intense or unaccustomed exercise, and in rare cases statins.

Ask for an urgent GP appointment or contact NHS 111 if you have throbbing pain and swelling in one leg, with red or darkened skin, as this could be a blood clot (DVT). Call 999 if leg pain and swelling come with breathlessness or chest pain.

See your GP if cramps disturb your sleep, last longer than 10 minutes, or come with numbness or swelling in your legs, and tell your doctor about any unexplained muscle pain, tenderness or weakness while taking a statin.

Frequently asked questions

Which deficiency causes muscle cramps?

Low magnesium, low calcium and low potassium are the minerals most linked to cramps. Low vitamin D can lower calcium and cause muscle weakness. A blood test can check all of these.

Can statins cause muscle cramps?

Yes. The NHS lists statins as a cause of leg cramps, and they can occasionally inflame muscles. A CK blood test helps your doctor decide whether to change your treatment. Do not stop a statin on your own.

Should I take magnesium for night cramps?

Check your level first and talk to your GP or pharmacist, especially if you have kidney disease or take other medicines. The NHS recommends regular calf stretches as a first step for night cramps.

Do I need to fast before the test?

You do not usually need to fast for these tests. Avoid very hard exercise in the days before if CK is being measured, as it can raise the result, and ask when you book if you are unsure.

Muscle cramp blood testing in Chiswick

Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick, London W4 1LZ, a short walk from Turnham Green station (District line; Piccadilly line trains stop there early morning and late evening only) and on the 94, E3 and 272 bus routes. Limited parking is available on request when you book. Every clinic test price includes your sample taken at the clinic, analysis at the Randox accredited laboratory, a review of your result with a practitioner and a GP feedback report on request. No GP referral is needed and most results are back within a few working days.

Book the Muscle and Joint Screen or the Vitamins and Minerals Check, or compare every blood test and price. For more detail, read our guides to magnesium levels and calcium levels.

This article is general information, not medical advice. Discuss your results with your GP or practitioner.