What is magnesium?
Magnesium is the quiet helper of your metabolism. More than three hundred enzymes need it, from the enzymes that make energy from food to the enzymes that copy your DNA and let your muscles relax after a contraction. It keeps the potassium channels in your cells closed, lets your parathyroid glands release PTH and lets your heart beat in a regular rhythm. Of all the magnesium in your body about sixty percent sits in your bones, almost all the rest in your cells, and only one percent in your blood. That one percent is what the test measures, and that is the limitation of this value. Your body keeps blood magnesium up by taking it from the bones and the cells, so the blood value stays normal for a long time while the store in the tissue is already shrinking. A low blood value therefore means the deficiency has existed for a while, and a normal value does not rule out a deficiency. The kidneys regulate removal: they hold on to magnesium when there is little and excrete it when there is plenty, and anything that disturbs that regulation shifts the value. Your report shows magnesium in mmol/L. Normal is about 0.73 to 0.98 mmol/L for a man and 0.77 to 0.98 mmol/L for a woman, where the labs overlap. Below 0.4 mmol/L and above 3.0 mmol/L the requester is phoned the same day, because the heart rhythm can then be at risk.
Why is magnesium relevant?
Magnesium is the value you read when potassium or calcium stay low while you top them up. Without magnesium the kidneys leak potassium away and the parathyroid glands release no PTH, so a low potassium and a low calcium only recover once magnesium is topped up. Anyone who takes diuretics, acid-reducing medicines or a lot of alcohol loses magnesium through the kidneys or does not absorb it, and that is the most common reason a low potassium or calcium will not correct. For anyone who is healthy and does sport, magnesium is more interesting than the blood value shows. Muscle cramps, twitching eyelids, poor sleep and a heart that skips are the symptoms of a deficiency in the tissue, and those can be there with a normal blood value. A diet with few nuts, seeds, legumes, whole grains and green vegetables and a lot of processed food delivers less magnesium than the body needs, and sweat carries it away. A generous intake from food goes with a lower blood pressure, a better blood sugar and less cardiovascular disease, and that is an effect of the store in the cells, not of the number in your blood. The upper end is almost always the kidneys. Healthy kidneys excrete every surplus, so a high magnesium means they can no longer do that, or that more comes in through medicines such as magnesium-containing laxatives or antacids than they can handle. A magnesium supplement hardly lifts the blood value with healthy kidneys.
Magnesium reference ranges
What counts beside the number:
- Potassium and calcium from the same draw, because those do not recover while magnesium is low
- Which medicines you take: acid-reducing medicines, diuretics and magnesium-containing laxatives or antacids
- How much alcohol you drink, and whether you have long-lasting diarrhoea or a bowel disease
- Creatinine and the eGFR, which say whether the kidneys can get rid of a surplus
- Your symptoms and your diet, because a normal blood value does not rule out a deficiency in the tissue
- Whether you take a magnesium supplement, and in which form and dose
More important than the margin between labs is what this test measures: your blood holds about one percent of all the magnesium in your body, and the rest sits in your bones and inside your cells. Your body keeps the blood value up by taking from that store, so a normal value does not rule out a deficiency in the tissue and a low value means the deficiency has existed for a while. A low potassium or calcium that will not recover is often the first clue.
What Dutch labs actually use
Three of the four labs publish one range for all adults and sit close together: Unilabs 0.70 to 1.00, Star-shl and Certe both 0.71 to 0.98. Clinical Diagnostics is the only one splitting by sex, with 0.73 to 1.06 for men and 0.77 to 1.03 for women. A woman at 0.74 mmol/L is therefore normal at three labs and too low at Clinical Diagnostics.
0.77 – 0.98mmol/L
Between 0.70 and 0.77 and between 0.98 and 1.03 it depends on the lab, because each sets its limits on its own method and population. Above 1.03 every lab calls it abnormal.
every lab calls 0.77 – 0.98 mmol/L normal. Between 0.70 and 0.77 and between 0.98 and 1.03 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | From 19 yrs | 0.70–1.00 mmol/L |
| Call-back limit, low | < 0.4 mmol/LDecision limit | |
| Call-back limit, high | > 3.0 mmol/LDecision limit | |
| Star-shl2026 | From 6 yrs | 0.71–0.98 mmol/L |
| Certe2026 | From 6 yrs | 0.71–0.98 mmol/L |
| Clinical Diagnostics2026 | Men | 0.73–1.06 mmol/L |
| Women | 0.77–1.03 mmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Magnesium high or low: what it means
A low magnesium almost always means loss or poor absorption, and rarely too little food alone. Usually it is the first and rarely the last: acid-reducing medicines, which with long-term use block absorption in the gut; diuretics, which make the kidneys release magnesium; and alcohol, which makes the kidneys excrete magnesium and often makes the diet one-sided. After that come long-lasting diarrhoea or a bowel disease, and a poorly controlled diabetes, in which the kidneys lose magnesium along with the sugar. The symptoms are cramps, twitching, tiredness and a heart that skips, and a low potassium or calcium that will not recover is often the first clue. A high magnesium means the kidneys cannot get rid of it. With kidneys that filter less, magnesium builds up, certainly if magnesium-containing laxatives, antacids or supplements are added. With healthy kidneys a high value is rare, and then usually a matter of dehydration or a tube in which the red cells broke. Above 3.0 mmol/L the muscles go weak and the heart slows, and that should be assessed the same day. What you do about it: with a low magnesium food is the first step, with nuts, seeds, legumes, whole grains, green leafy vegetables, cocoa and mineral water, and less alcohol. If the value is really low or a potassium or calcium stays low, a supplement is the way; magnesium citrate or glycinate is absorbed better than the cheaper oxide, and a lot in one go gives diarrhoea, so spread it over the day. With acid-reducing medicines or diuretics the question is whether the drug stays necessary, and you discuss that with whoever prescribed it. With a high magnesium from medicines you stop them, and with kidneys that work less it belongs to the values a kidney specialist follows. Magnesium belongs beside potassium and calcium, because those do not recover while magnesium is low, beside creatinine and the eGFR, which say whether the kidneys can get rid of it, and beside your symptoms and your diet, because a normal blood value does not rule out a deficiency in the tissue.
What lowers it
Loss through the kidneys or the gut, or an absorption that is blocked.
| Cause | How often |
|---|---|
| Acid-reducing medicationWith long-term use they block absorption in the gut; the most common reason in anyone who has taken them for years, and after stopping the value recovers | Often |
| DiureticsThe kidneys release magnesium along with the water; often together with a low potassium that will not correct | Often |
| AlcoholMakes the kidneys excrete magnesium and often makes the diet one-sided; in anyone who drinks a lot a deficiency is the rule | Often |
| Prolonged diarrhoeaGut fluid is full of magnesium; a bowel disease or stomach surgery also lower absorption | Sometimes |
| Poorly controlled diabetesThe kidneys lose magnesium along with the sugar; it recovers once the blood sugar comes under control | Rare |
What raises it
The kidneys cannot get rid of it, or more comes in through medicines than they can handle.
| Cause | How often |
|---|---|
| Reduced kidney functionHealthy kidneys excrete every surplus; with a low eGFR magnesium builds up, and creatinine shows the kidney | Often |
| Magnesium-containing medicinesLaxatives, antacids and high-dose supplements; rarely a problem with healthy kidneys, a problem with weaker kidneys | Sometimes |
How does a magnesium blood test work?
- Referral
- Not needed. You can have magnesium measured yourself, preferably with potassium, calcium and creatinine alongside.
- Fasting
- Not needed; the blood value hardly moves with a meal. Skip a magnesium supplement on the day of the draw.
- When
- Not straight after a hard training session or a day of heavy sweating, and not during diarrhoea, if you want to know your usual level.
- The draw
- One tube of blood from a vein in your arm, with a loose tourniquet and a relaxed hand, because broken red cells release magnesium and lift the value.
- Repeating
- Three months after starting a supplement or stopping an acid-reducing medicine, to see whether the value recovers. Anyone who keeps taking diuretics or acid-reducing medicines measures once a year.
- Which test
- Magnesium is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 350+ locations near you, no referral needed. See the locations
Frequently asked questions
The mineral that drives more than three hundred enzymes in your cells: the enzymes that make energy from food, copy your DNA and let your muscles relax after a contraction. It keeps the potassium channels in your cells closed, lets your parathyroid glands release PTH and keeps your heart in a regular rhythm. Sixty percent sits in your bones, almost all the rest in your cells, and only one percent in your blood.
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): magnesium. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): magnesium. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): magnesium. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): magnesium. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
- 6.Costello et al., Perspective: The Case for an Evidence-Based Reference Interval for Serum Magnesium: The Time Has Come, Advances in Nutrition. 2016. doi.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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