What is the Magnesium (Serum) Test?

The Magnesium (Serum) test measures the concentration of magnesium circulating in the blood. Magnesium is an essential mineral involved in over 300 enzymatic reactions, playing a key role in muscle contraction, nerve transmission, energy production and heart rhythm regulation.

Serum magnesium reflects the body’s available magnesium at the time of testing. While most magnesium is stored in bones and tissues, abnormal serum levels can indicate deficiency, excess intake or underlying medical conditions affecting absorption or excretion.

This test is commonly used in routine health screening, hospital monitoring and investigation of neuromuscular or cardiac symptoms.

Why do I need a test for Magnesium (Serum)?

You may need this test if you have symptoms suggestive of magnesium imbalance or if you have conditions that affect mineral absorption or loss. Magnesium deficiency is relatively common and can be overlooked, particularly in people with gastrointestinal disorders, kidney disease or certain medication use.

Monitoring magnesium levels supports early intervention, helping prevent complications such as arrhythmias, muscle dysfunction and metabolic disturbances.

Symptoms and scenarios where testing is recommended:

• Muscle cramps or spasms
• Fatigue or weakness
• Irregular heartbeat or palpitations
• Numbness or tingling
• Headaches or migraines
• Digestive disorders affecting absorption
• Diuretic or proton pump inhibitor use
• Chronic kidney or metabolic conditions

Benefits of the Magnesium (Serum) Test

• Assesses essential mineral status
  Evaluates magnesium availability in the bloodstream.
• Supports neuromuscular health assessment
  Helps explain cramps, spasms and weakness.
• Monitors heart rhythm risk
  Magnesium is critical for cardiac electrical stability.
• Identifies deficiency or excess
  Detects imbalance before severe symptoms develop.
• Guides supplementation decisions
  Supports safe and targeted magnesium replacement.
• Useful in hospital and outpatient settings
  Commonly used in acute and chronic care.
• Supports metabolic health monitoring
  Magnesium is involved in glucose and energy metabolism.
• Simple and widely accepted test
  Requires only a standard blood sample.

Step-by-Step: How Testing Works

Choose your preferred testing method

You can attend one of our UK partner clinics or arrange a home or hotel visit with a mobile phlebotomist.

Option 1 – In-Clinic Blood Draw

1. Select your nearest UK clinic and book an appointment.
2. A clinician or phlebotomist collects a venous blood sample.
3. The sample is analysed for serum magnesium levels.
4. Results are delivered securely online.

Option 2 – Home or Hotel Phlebotomy (+£60)

1. Book a UK-wide home or hotel visit at a convenient time.
2. A trained phlebotomist collects your blood sample on-site.
3. The sample is transported to the laboratory.
4. Results are uploaded digitally without the need to travel.

Your Results Explained

Low Levels

Low serum magnesium may indicate dietary deficiency, malabsorption, increased loss via kidneys or gastrointestinal tract, or medication effects.
Symptoms may include muscle cramps, fatigue and heart rhythm disturbances.
Typical UK reference range: approximately 0.70–1.00 mmol/L.

Normal Levels

Normal magnesium levels suggest adequate circulating magnesium and stable mineral balance.
This supports normal neuromuscular and cardiovascular function.

High Levels

Elevated magnesium levels are less common and may occur with excessive supplementation or impaired kidney function.
High levels can cause lethargy, low blood pressure and cardiac conduction abnormalities.