Is Magnesium Included in a Comprehensive Metabolic Panel (CMP)?
No, magnesium is not included in a standard Comprehensive Metabolic Panel (CMP) and must be ordered separately as an additional test.
What is Actually Included in a CMP
A CMP is defined as a panel that includes "basic chemistries and liver function tests" 1. The standard components are:
- Electrolytes: sodium, potassium, chloride, bicarbonate
- Kidney function: blood urea nitrogen (BUN), creatinine
- Liver function: ALT, AST, alkaline phosphatase, total bilirubin, albumin, total protein
- Glucose
- Calcium
When Magnesium Must Be Ordered Separately
Clinical guidelines consistently demonstrate that magnesium requires separate ordering alongside a CMP when monitoring is needed:
- When monitoring cyclosporine therapy, guidelines specify ordering "CBC, CMP, magnesium, uric acid, lipids, and blood pressure" as distinct tests 1
- For tacrolimus monitoring, protocols require "CMP, magnesium, phosphorus monitored 1-2 times per week" 1
- These recommendations explicitly list magnesium separately from the CMP, confirming it is not included 1
Why This Matters Clinically
Magnesium deficiency is common but easily missed because it requires specific testing:
- Approximately 45% of Americans are magnesium deficient, yet serum magnesium is not routinely measured 2
- Serum magnesium levels represent less than 1% of total body magnesium, making deficiency difficult to detect without specific testing 3, 4
- Magnesium deficiency is associated with hypertension, diabetes, cardiac arrhythmias, and refractory hypokalemia 5, 2
Common Clinical Pitfall
The most critical error is assuming a "normal" CMP rules out magnesium abnormalities. Clinicians must specifically order serum magnesium when:
- Monitoring medications that affect magnesium (cyclosporine, tacrolimus, diuretics) 1
- Evaluating refractory hypokalemia 5
- Assessing patients with malabsorption, short bowel syndrome, or chronic diarrhea 5
- Managing cardiac arrhythmias, particularly torsades de pointes 5
Always order magnesium as a separate test when clinical suspicion exists—it will not be captured by a standard CMP.