Magnesium is an important element in the functioning of many systems in the human body, in particular, the function of the heart and muscles. Magnesium is absorbed in the small intestine and then distributed to all the cells and stored within the bones. Any excess is eliminated by the kidneys in the form of urine. In the setting of renal failure, where the kidneys are not functioning well or at all, magnesium levels are impacted. Also, various medications can lead to either magnesium loss or retention.
Terminology
Chronic renal failure is a vague term used by some health care providers that can refer to anything from slight kidney dysfunction to end stage kidney disease requiring some form of therapy to replace the function of the kidneys, such as dialysis. Typically, a patient with chronic kidney disease is in stages 3 through 5, as defined by the National Kidney Foundation Kidney Disease Outcomes Quality Initiates guidelines, and not on any form of therapy to replace the function of the kidneys.
Chronic Kidney Disease and Magnesium
Patients with chronic kidney disease can have either high or low magnesium levels. The only commercially available way to measure magnesium is with a blood test. This blood test is not perfect and does not measure total body stores. In chronic kidney disease stage 3, patients can have magnesium losses, either due to certain medications or intrinsic kidney problems, and require supplementation. Supplementation is determined based on the blood test. Most providers adjust the magnesium supplementation to get the magnesium level in the blood back within the normal range. As kidney disease progresses, going from stage 3 to stage 5, the kidneys are less able to handle magnesium and the risk of magnesium toxicity increases.
Toxicity
Magnesium toxicity can be life threatening and is generally related to muscle and heart function. Symptoms, such as weakness, begin when the blood level is greater than 3.6 mg/dL. When greater than 7.2 mg/dL, reflexes are lost and, when greater than 12 mg/dL, there is an increased risk of low blood pressure, loss of consciousness, respiratory failure -- because the muscles that control the breathing no longer function -- and heart rhythm problems. Such severe toxicity is usually related to overdosing of magnesium supplementation.
Dosing
The safest dose of magnesium supplementation in chronic renal failure is the dose determined by the health care provider, ideally a nephrologist. This is usually done with monitoring of blood levels of magnesium. If you think you might need magnesium supplementation or are curious, discuss this with your health care provider before you begin any changes to your medication regimen.
References
- "Comprehensive Clinical Nephrology"; John Feehally, et al.; 2007
- National Kidney Foundation; KDOQI Guidelines; 2000
- "Blood Purification"; Magnesium in Chronic Kidney Disease: Challenges and Opportunities; Mehmet Kanbay, et al.; January 2010
