Does a CMP Include eGFR?
Yes, a Comprehensive Metabolic Panel (CMP) typically includes an estimated Glomerular Filtration Rate (eGFR) calculation based on the serum creatinine value that is part of the panel.
Components of a CMP and eGFR Calculation
A standard Comprehensive Metabolic Panel includes:
Kidney function markers:
- Serum creatinine
- Blood Urea Nitrogen (BUN)
- eGFR (calculated from serum creatinine)
Electrolytes:
- Sodium
- Potassium
- Chloride
- Carbon dioxide (CO2)
Liver function tests:
- Albumin
- Total protein
- Bilirubin
- Alkaline phosphatase (ALP)
- Alanine aminotransferase (ALT)
- Aspartate aminotransferase (AST)
Glucose
eGFR Calculation in Clinical Practice
The eGFR is not directly measured in the blood sample but is calculated from the serum creatinine value using validated equations 1, 2. Most laboratories automatically report eGFR alongside serum creatinine as a standard practice when processing a CMP.
Common eGFR Calculation Methods:
- CKD-EPI equation: The most widely used equation, recommended by KDIGO guidelines 1
- MDRD Study equation: An older equation still used in some settings
- Cockcroft-Gault equation: Used primarily for medication dosing
Clinical Significance and Interpretation
The inclusion of eGFR in CMP reporting provides several important clinical benefits:
- Improved detection of kidney disease: eGFR is more sensitive than serum creatinine alone for detecting early kidney dysfunction 3
- Standardized assessment: Provides a standardized method for assessing kidney function across different patient populations
- Clinical decision-making: Facilitates appropriate timing of nephrology referrals and medication adjustments 3
Important Considerations
When interpreting eGFR results from a CMP:
- Non-GFR determinants: eGFR calculations are influenced by factors such as muscle mass, diet, medications, and certain disease states 2
- Race considerations: Many laboratories have moved away from race-based eGFR calculations following recommendations from the NKF-ASN Task Force 1
- Confirmation options: For critical clinical decisions, consider confirming with cystatin C-based eGFR (eGFRcys) or measured GFR when eGFRcr may be inaccurate 1, 2
Laboratory Reporting Standards
According to KDIGO guidelines, laboratories should 1:
- Report eGFR in addition to serum creatinine
- Round eGFR to the nearest whole number
- Flag eGFR values <60 mL/min/1.73 m² as being low
- Report units as mL/min/1.73 m²
In summary, while the eGFR is not directly measured in the blood sample, it is a calculated value derived from serum creatinine that is routinely included in CMP reporting by most clinical laboratories.