Does a Comprehensive Metabolic Panel Monitor Serum Calcium?
Yes, a Comprehensive Metabolic Panel (CMP) includes serum calcium measurement as one of its 14 standard components. 1, 2
Components of the CMP
The CMP is a standardized panel that measures:
- Electrolytes: sodium, potassium, carbon dioxide (bicarbonate), and chloride 1, 2
- Kidney function tests: blood urea nitrogen (BUN) and creatinine 2
- Glucose 2
- Liver function tests: aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase, total bilirubin, albumin, and total protein 1, 2
- Serum calcium 1, 2
Clinical Context and Interpretation
When interpreting calcium results from a CMP, you must correct for albumin levels, as the CMP provides total calcium rather than ionized (free) calcium. 1, 3 The correction formula recommended by K/DOQI guidelines is:
Corrected total calcium (mg/dL) = Total calcium (mg/dL) + 0.8 [4 - Serum albumin (g/dL)] 1, 3
This correction is essential because:
- Low albumin falsely lowers total calcium measurements 3
- Approximately 40% of total calcium is protein-bound, 48% is ionized (physiologically active), and 12% is complexed with anions 3
- The corrected value better reflects the clinically relevant free calcium 3
Important Clinical Considerations
The inclusion of calcium in the CMP has led to a dramatic increase in calcium testing volumes without corresponding increases in calcium-related diagnoses. 4 A 2020 study found that implementation of AMA-approved panels increased total calcium test volumes by more than 3-fold, with the majority coming from BMPs and CMPs, yet the prevalence of hypo- and hypercalcemia-related diagnoses remained unchanged (1.29% before vs 1.27% after implementation). 4
Normal reference ranges for calcium are:
- Total serum calcium: 8.6 to 10.3 mg/dL (2.15 to 2.57 mmol/L) 3
- Ionized calcium: 4.65 to 5.28 mg/dL (1.16 to 1.32 mmol/L) 3
- For CKD patients, maintain calcium toward the lower end of normal (8.4 to 9.5 mg/dL) 3
When to measure ionized calcium directly instead of relying on CMP total calcium:
- Subtle calcium changes are expected 3
- Plasma protein levels are abnormal 3
- Acid-base disturbances are present 3
- Total calcium measurements with correction formulas are inadequate 3
Note that ionized calcium measurement has worse reproducibility and higher cost than total calcium, limiting its routine use. 3