Magnesium Blood Test
Feb 11, 2026
Magnesium Blood Test
A magnesium blood test measures the magnesium level in your blood—with deficiency affecting up to 50% of the population and causing symptoms including muscle cramps, twitches, fatigue, anxiety, poor sleep, headaches, and heart palpitations. Magnesium is involved in over 300 biochemical reactions in your body, making adequate levels essential for health.
At Blood Test London, magnesium testing costs from £245 with results in 2-3 days.
Why Magnesium Matters
Magnesium is essential for:
Muscle function (relaxation after contraction)
Nerve function (signal transmission)
Energy production (ATP requires magnesium)
Heart rhythm (electrical stability)
Sleep quality (GABA activation)
Bone health (60% of magnesium is in bones)
Blood sugar control (insulin sensitivity)
Blood pressure (vasodilation)
Normal Magnesium Levels
Level (mmol/L) | Interpretation |
|---|---|
Below 0.7 | Deficient |
0.7-0.85 | Low normal (may still be suboptimal) |
0.85-1.0 | Optimal |
Above 1.0 | High (usually from supplements/medication) |
Important: Serum magnesium only reflects 1% of body stores. You can have low tissue magnesium with "normal" serum levels. Red blood cell magnesium is more accurate but less available.
Signs of Magnesium Deficiency
Muscular
Muscle cramps and spasms
Twitches (especially eyelid)
Restless leg syndrome
Muscle weakness
Tension headaches
Neurological/Mental
Anxiety and irritability
Poor sleep
Fatigue
Brain fog
Depression
Cardiovascular
Heart palpitations
Irregular heartbeat
High blood pressure
Other
Constipation
PMS symptoms
Migraines
Asthma (magnesium relaxes airways)
Who's at Risk of Deficiency?
Stressed individuals (stress depletes magnesium)
Athletes (lost through sweat)
Diabetics (increased urinary loss)
Alcohol drinkers (impairs absorption)
Those on certain medications (PPIs, diuretics)
Digestive disorders (Crohn's, coeliac)
Elderly (reduced absorption)
Poor diet (processed foods lack magnesium)
How to Optimise Magnesium
Food Sources
Food | Magnesium (mg per serving) |
|---|---|
Pumpkin seeds (30g) | 156 |
Spinach (cooked, 1 cup) | 157 |
Dark chocolate (30g) | 65 |
Almonds (30g) | 80 |
Avocado (1 medium) | 58 |
Black beans (1 cup) | 120 |
Salmon (100g) | 30 |
Daily requirement: 300-400mg
Supplementation
Form | Notes |
|---|---|
Magnesium glycinate | Best absorbed, good for sleep |
Magnesium citrate | Good absorption, can loosen stools |
Magnesium threonate | Crosses blood-brain barrier |
Magnesium malate | Good for energy and muscles |
Magnesium oxide | Cheap but poorly absorbed |
Tips
Split doses throughout day (better absorption)
Take with food
Vitamin D helps magnesium absorption
Avoid taking with calcium (they compete)
Book Your Magnesium Test
Price: From £245
Results: 2-3 days
Doctor review: A doctor always reviews every result
Fasting required: No
Phone: 020 3951 3429
FAQ
Can I have low magnesium with a normal blood test?
Yes—serum magnesium only reflects 1% of body stores. You may be tissue-depleted but test normal. Symptoms and response to supplementation also guide assessment.
Is it safe to supplement magnesium?
Generally yes. Excessive intake may cause loose stools (your body's signal to reduce dose). Those with kidney disease should be cautious.
How long to correct deficiency?
With supplementation, levels improve in weeks, but replenishing tissue stores may take 3-6 months.
Blood Test London by The Wellness. Magnesium testing from £245, results in 2-3 days.