From the Guidelines
Blood magnesium testing is not an accurate measurement of magnesium status because less than 1% of magnesium stores are in the blood. This is according to the British Society of Gastroenterology consensus guidelines on the management of inflammatory bowel disease in adults 1.
Key Points to Consider
- Magnesium deficiency has been reported to occur in 13–88% of patients with IBD, but serum magnesium levels do not accurately reflect this due to the small proportion of magnesium in the blood.
- The majority of magnesium is stored in bone, soft tissue, and muscle, making serum magnesium a poor indicator of overall magnesium status.
- Symptoms of magnesium deficiency, such as abdominal cramps, impaired healing, fatigue, and bone pain, should be considered alongside blood test results.
- Healthcare providers may need to use alternative methods, such as red blood cell magnesium testing or magnesium loading tests, to get a more accurate assessment of magnesium status 1.
Factors Affecting Test Accuracy
- Recent magnesium intake
- Certain medications (e.g., diuretics, proton pump inhibitors)
- Kidney function
- Sample handling techniques in the laboratory It is essential to interpret blood test results in the context of these factors and consider clinical symptoms and risk factors for deficiency to make an informed decision about magnesium supplementation.
From the Research
Accuracy of Testing Magnesium Levels in the Blood
The accuracy of testing magnesium levels in the blood is a topic of ongoing discussion in the medical community.
- Magnesium is an essential element for maintaining normal cellular and organ function, and inadequate magnesium balance can lead to various disorders 2.
- However, routinely measured serum magnesium levels do not always reflect total body magnesium status, which can lead to widespread magnesium deficiency being overlooked 2.
- Other methods, such as the magnesium loading test, may provide more accurate reflections of total body magnesium status 2.
Limitations of Serum Magnesium Tests
- Serum magnesium concentration is maintained for a long time by releasing magnesium from body pools, which limits its informative value 3.
- A low serum magnesium is a definite sign of magnesium deficiency, but values within the reference range do not rule out deficiencies 3.
- The traditional method of establishing a reference interval for serum magnesium concentration is flawed due to the large number of "normal" individuals with a subtle chronic negative magnesium balance 4.
Recommendations for Assessment of Magnesium Status
- A combination of available tests is recommended to assess magnesium status, including determining total magnesium in tissues and physiologic tests 5.
- A test for the routine determination of free magnesium in serum could improve the assessment of magnesium status 5.
- Evidence-based medicine should be used to establish the appropriate lower limit of the reference interval for health, with a recommended lower limit of 0.85 mmol/L 3, 4.