Magnesium (Whole Blood)
The whole blood magnesium test measures magnesium inside blood cells. It reflects long-term magnesium status more accurately than serum testing.
Turnaround time
1-2 days
Biomarkers count
1
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Details about Magnesium (Whole Blood)
What is the Magnesium (Whole Blood) test?
The Magnesium (Whole Blood) test measures magnesium levels in whole blood, including red blood cells, rather than just serum. Because most magnesium is stored inside cells, whole blood testing provides a more accurate reflection of intracellular and long-term magnesium status.
Magnesium is essential for muscle and nerve function, heart rhythm regulation, energy production, bone health, and glucose metabolism. Serum magnesium can remain normal even when cellular deficiency exists, making whole blood measurement clinically valuable.
This test is often preferred when magnesium deficiency is suspected despite normal serum results.
Why do I need a test for Magnesium (Whole Blood)?
Magnesium deficiency is common and frequently overlooked. Chronic low levels can contribute to cardiovascular, neurological, metabolic, and muscular symptoms.
Whole blood testing helps uncover hidden or functional magnesium deficiency, particularly in people with ongoing symptoms or increased magnesium demand.
You may benefit from this test if you experience:
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Muscle cramps, spasms, or twitching
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Heart palpitations or irregular heartbeat
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Fatigue or low energy
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Anxiety or poor sleep
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Headaches or migraines
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Insulin resistance or blood sugar issues
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Digestive or absorption problems
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Long-term stress or high physical demand
Benefits of the Magnesium (Whole Blood) test
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Reflects true cellular magnesium status
Measures magnesium inside blood cells, not just serum. -
More accurate than serum magnesium
Detects deficiency missed by standard tests. -
Supports cardiovascular health assessment
Magnesium is critical for heart rhythm stability. -
Useful in muscle and nerve symptoms
Low levels contribute to cramps and neuromuscular issues. -
Relevant for metabolic health
Magnesium plays a role in glucose and insulin regulation. -
Supports stress and nervous system evaluation
Chronic stress depletes magnesium stores. -
Guides targeted supplementation
Helps personalise magnesium support strategies. -
Non-invasive nutritional assessment
Requires only a blood sample.
Step-by-step – how we offer Magnesium (Whole Blood) testing
Clinic-based testing (UK-wide)
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Choose your nearest UK clinic
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Attend your appointment
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Blood sample collected by a qualified clinician or phlebotomist
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Sample is sent to the laboratory for analysis
At-home or hotel testing (+£60)
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A qualified phlebotomist visits your home or hotel
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Blood sample collected in a comfortable, familiar setting
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No clinic visit or travel required
Both services are available UK-wide.
Your Magnesium (Whole Blood) results explained
Low whole blood magnesium
Low levels indicate intracellular magnesium deficiency. This may affect muscle function, heart rhythm, nervous system balance, and energy production.
Causes include poor intake, malabsorption, chronic stress, certain medications, or increased losses.
UK reference interpretation:
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Low: Below laboratory reference range
Normal whole blood magnesium
Normal levels suggest adequate cellular magnesium availability. This supports neuromuscular function, cardiovascular stability, and metabolic processes.
Symptoms may still occur if other nutrients are imbalanced.
UK reference interpretation:
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Normal: Within laboratory reference range
High whole blood magnesium
High levels are uncommon and usually related to excessive supplementation or reduced kidney clearance. Elevated magnesium may cause lethargy, low blood pressure, or slowed reflexes.
Clinical context is essential.
UK reference interpretation:
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High: Above laboratory reference range
How It Works
Simple steps to get your results
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Choose your test online and book in seconds. Select your preferred clinic location or home visit option.
Visit or Test at Home
Attend one of our UK or London clinics, arrange a home nurse visit, or use a finger-prick kit where available.
Get Your Results
Your sample is analysed by accredited UK laboratories, with secure results delivered directly to you.
Take control of your health with London Blood Tests
WhatsApp UsHow to Prepare for Your Test
Follow these guidelines for accurate results
Sample Timing
Where possible, attend your blood test between 7am and 12pm. Please wait until any short-term illness or infection has fully resolved before testing. Avoid intense exercise for 24–48 hours beforehand, as this can affect certain markers.
Fasting & Hydration
Fasting is not always required, but some tests may recommend it. If fasting is advised, avoid food for 8–12 hours before your appointment and drink water only. Stay well hydrated, as this helps with sample collection and accuracy.
Medications & Supplements
Continue prescribed medications unless advised otherwise by your clinician. Avoid vitamin, mineral, or biotin supplements for at least 24–48 hours before your test, as these can interfere with results. If you are unsure about any medication or supplement, please let us know before your appointment.
Hormones & Menstrual Cycle
For hormone-related tests, timing within your menstrual cycle may be important. If relevant, follow any specific guidance provided on your test page.
If you have any questions or special circumstances, our team is happy to advise before your appointment.