Vitamins, minerals and amino acids
Magnesium
The magnesium in your blood; mainly shows large deficiencies or excesses and says little about the store in your body.
Everything about this testWhat it measures
Magnesium is a mineral needed for muscles, nerves, bones and energy production in cells. About half is in the bones and the rest mainly in cells, muscles and organs; only about 1 percent is in the blood. The intestines and kidneys keep the amount in the blood within narrow limits by absorbing and excreting more or less. This analysis measures the magnesium in serum.
- A magnesium level that is too low (hypomagnesemia) due to loss or poor absorption, for example with prolonged diarrhea, water pills (diuretics), stomach acid inhibitors (proton pump inhibitors), bowel diseases or a lot of alcohol
- A magnesium level that is too high (hypermagnesemia), mainly with reduced kidney function or use of laxatives containing magnesium
- A possible explanation for a persistently low potassium or calcium
High
According to the Dutch Society for Clinical Chemistry (NVKC), a raised magnesium is rarely caused by diet. It is usually due to reduced kidney function, which makes the body less able to get rid of magnesium, or to magnesium from laxatives or high-dose supplements. Dehydration can also raise the value. A slightly raised value usually causes no symptoms. With a finger prick or a difficult blood draw, damaged blood cells (hemolysis) can release magnesium, making the result falsely high.
Low
A low magnesium mainly results from loss or poor absorption: prolonged diarrhea, a lot of alcohol, malnutrition, bowel diseases such as Crohn's disease, water pills (diuretics), long-term use of stomach acid inhibitors (proton pump inhibitors) and poorly controlled diabetes. According to Het Acute Boekje of the Dutch internists, symptoms usually only appear at a strongly low value (below 0.5 mmol/l), often because potassium and calcium then also fall: muscle weakness, trembling, cramps and heart rhythm disorders. Vague symptoms such as tiredness or muscle cramps usually have another cause; according to Thuisarts, magnesium does not help against nighttime calf cramps, except sometimes during pregnancy. A normal value does not rule out a small deficiency in the cells.
If your result is abnormal
With a low magnesium, the GP looks at medicines (water pills, stomach acid inhibitors), alcohol use and bowel symptoms, and usually also measures potassium, calcium and kidney function. With a raised magnesium, kidney function is checked and the use of laxatives or supplements is asked about.
Reliability
The measurement itself is reliable, but serum magnesium poorly reflects the store in the body, because only about 1 percent of the magnesium is in the blood and the body keeps that value stable. The Netherlands Nutrition Centre (Voedingscentrum) therefore writes that the blood value is not a good measure for establishing a magnesium deficiency. The measurement is mainly useful with illness, medicine use or an abnormal potassium or calcium. There is no Dutch GP guideline (NHG) that recommends measuring magnesium in people without symptoms.
Limitations
- Hemolysis due to a finger prick, prolonged use of a tourniquet or a difficult blood draw can falsely raise the value.
- Magnesium supplements and laxatives raise the value; water pills (diuretics) and stomach acid inhibitors can lower it.
- Reference values differ between laboratories.
How common is this
How often a low magnesium occurs in healthy Dutch people is not known. According to the Netherlands Nutrition Centre (Voedingscentrum), a deficiency does not occur easily, because magnesium is found in many foods, such as whole grain products, vegetables, nuts and dairy products. A low magnesium is mainly seen with bowel or kidney problems, a lot of alcohol and long-term use of water pills or stomach acid inhibitors.
Who is this useful for
Useful with prolonged diarrhea or a bowel disease, heavy alcohol use, malnutrition, long-term use of water pills (diuretics) or stomach acid inhibitors (proton pump inhibitors), reduced kidney function and a persistently low potassium or calcium. With tiredness or muscle cramps without these risk factors, the measurement is of little use, because a deficiency is rarely the cause and the blood value does not show a small deficiency well. A vegetarian diet is also not expected to cause a deficiency, because magnesium is abundant in plant-based products.
Downsides and risks
- A slightly abnormal result is easily seen as the explanation for vague symptoms such as tiredness or cramps; this can lead to unnecessary supplement use while another cause is missed.
- According to the Netherlands Nutrition Centre (Voedingscentrum), more than 250 milligrams of magnesium per day from supplements can cause diarrhea.
Sources
Always discuss an abnormal result with your GP. If a result is strongly abnormal, we try to reach you as soon as possible. Read your result yourself as well and contact your GP if in doubt. A test does not make a diagnosis. Read more about risks and results