Low Magnesium Levels: What Does the Blood Test Mean?

Low magnesium levels mean the amount of magnesium in a blood sample is below the laboratory's reference range. The medical name is hypomagnesaemia. It usually happens because the body is losing too much magnesium through the gut or kidneys, not absorbing enough, or not getting enough in the diet.

Magnesium is a mineral and an electrolyte. MedlinePlus explains that most of the body's magnesium is stored in bones, organs and other tissues, and only a small amount is in the blood. So a blood result is a useful signal, but it shows only a small share of the body's total magnesium.

Laboratories use different methods, units and ranges, so compare your result with the range printed on your own report and ask the clinician how far outside it you are.

Severely low magnesium can be life-threatening. MedlinePlus warns that, left untreated, it can lead to cardiac arrest or respiratory arrest. Do not wait for a routine repeat test if you have serious symptoms.

Call your local emergency number or go to the nearest hospital straight away for:

• A seizure (fit or convulsion).
• An abnormal, irregular or racing heartbeat, especially with fainting, chest pain or breathlessness.
• New confusion or delirium.
• Severe muscle spasms or cramps that will not stop, particularly if you have been told your magnesium, potassium or calcium is low.

Some people have no symptoms, and a low level is found on a blood test done for another reason. When symptoms do occur, they are often vague at first.

Milder symptoms listed by MedlinePlus, Cleveland Clinic and Healthdirect include loss of appetite, nausea and vomiting, tiredness, weakness, muscle cramps or spasms, tremor, and numbness or tingling. More severe low magnesium can cause abnormal eye movements, seizures, confusion and abnormal heart rhythms.

MedlinePlus and Cleveland Clinic group the causes into a few patterns. More than one can apply at the same time.

When the cause is not obvious, the clinician may ask about bowel habits, alcohol, diet, blood sugar control and every medicine or supplement you take. A urine magnesium test can help show whether the kidneys are losing magnesium.

• Losing magnesium through the gut: long-lasting or severe diarrhoea.
• Losing magnesium through the kidneys: uncontrolled diabetes with high blood glucose, alcohol use, certain kidney tubule disorders (such as Gitelman syndrome), and some medicines.
• Poor absorption: digestive conditions such as coeliac disease or inflammatory bowel disease (including Crohn's disease), and gastric bypass surgery.
• Low intake: malnutrition, alcohol use disorder with a poor diet, or critical illness without eating.
• Other causes listed by MedlinePlus: pancreatitis, large burns, heavy sweating, hyperaldosteronism and underactive parathyroid glands. Pregnancy also increases the body's need for magnesium.

Several medicines can lower magnesium, mainly by increasing loss through the kidneys or reducing absorption. Sources name diuretics (water tablets such as hydrochlorothiazide or furosemide), proton pump inhibitors for reflux, aminoglycoside antibiotics, some chemotherapy (such as cisplatin), and immunosuppressants (such as ciclosporin and tacrolimus). Healthdirect also lists some diabetes medicines and antivirals.

If you take a proton pump inhibitor long term, our separate guide on PPIs and low magnesium covers that link in detail. Do not stop or change a prescribed medicine without talking to the prescriber. The medicine may be important for another condition, and the clinician can weigh the benefits and look for other causes.

Cleveland Clinic notes that low magnesium often happens alongside low calcium and low potassium. MedlinePlus explains that magnesium plays a role in how the body handles calcium and potassium, which is why a magnesium test may be ordered to find the cause of abnormal levels of these minerals.

In practice, this means a clinician seeing a low potassium or low calcium result may check magnesium too, and the reverse. Some of the same causes, such as diarrhoea, diuretics and alcohol, can lower more than one at once. Our guides on low potassium and low calcium explain those results in more detail.

The clinician will usually look at how low the level is, any symptoms, other electrolytes and your medicines and health conditions. Cleveland Clinic lists related tests such as calcium, potassium, a wider metabolic panel, urine magnesium and an ECG (heart tracing).

According to Cleveland Clinic, mild cases are usually treated with magnesium by mouth, while severe cases need hospital care with magnesium given into a vein. The underlying cause is also treated. Do not start supplements on your own to correct a result; ask the clinician or pharmacist what is suitable, as supplements can interact with other medicines and kidney problems change how magnesium is handled.

People with a long-term cause, such as Crohn's disease or an inherited kidney tubule disorder, may need regular checks.

Bring your result, the reference range, the date of the test and a list of all medicines and supplements you take.

• How low is my magnesium compared with the lab's range, and is it mild or severe?
• What do you think is causing it, and could any of my medicines play a part?
• Were my potassium and calcium checked at the same time, and are they normal?
• Do I need treatment, and should it be by mouth or in hospital?
• Do I need an ECG or other tests?
• When will the level be rechecked, and who will contact me with the result?
• Which symptoms mean I should seek help before the next test?

On SameCase, patients and verified doctors share de-identified cases. Reading how others with low magnesium alongside diarrhoea, diuretics, diabetes or low potassium described their tests and follow-up can help you notice questions to raise. Other people's cases cannot tell you your cause or the right treatment; your own care team needs to interpret your results.