Does a Basic Metabolic Panel Check for GFR?
Yes, a Basic Metabolic Panel (BMP) does assess GFR because it includes serum creatinine, and clinical laboratories are required to automatically calculate and report estimated GFR (eGFR) alongside the creatinine value. 1
What You Get with a BMP
A BMP routinely includes serum creatinine measurement as one of its standard components, along with electrolytes, glucose, and blood urea nitrogen (BUN). 1
Clinical laboratories must automatically report eGFR in addition to the serum creatinine concentration using validated equations—this is a laboratory implementation standard established by KDIGO guidelines. 2, 1
The eGFR is calculated using the 2021 race-free CKD-EPI equation, which incorporates your patient's serum creatinine value from the BMP along with age and sex, without requiring any additional testing or urine collection. 1, 3
How eGFR is Reported
The eGFR should be reported rounded to the nearest whole number, expressed as mL/min per 1.73 m², and any values below 60 mL/min per 1.73 m² must be flagged as being low. 2, 1
This eGFR serves as the best available index of kidney function and is used to diagnose chronic kidney disease, classify its stages, and monitor disease progression. 1, 4
Normal eGFR is typically >60 mL/min/1.73 m², and values below this threshold may indicate chronic kidney disease according to KDIGO classification. 1, 4
Important Limitations to Recognize
eGFR from a BMP is "not sufficiently accurate and precise" compared to measured GFR and is subject to multiple non-GFR determinants that can significantly compromise reliability. 3
eGFR may be less accurate in patients with extremes of muscle mass (very low or very high), very elderly patients, extremes of body size, severe malnutrition, muscle wasting diseases, advanced cirrhosis, or cancer with high cell turnover. 1, 3
Medications affecting creatinine secretion (trimethoprim, cimetidine) or anabolic steroids also compromise eGFR accuracy. 3
When the BMP's eGFR is Not Enough
When eGFR from the BMP is expected to be inaccurate and GFR affects clinical decision-making, measure serum cystatin C and calculate eGFRcr-cys (combined creatinine-cystatin C equation). 3
For critical drug dosing decisions (chemotherapy, highly nephrotoxic drugs with narrow therapeutic windows), measured GFR using exogenous filtration markers (iothalamate, iohexol) is the gold standard. 3
If measured GFR is unavailable and eGFRcr-cys is thought inaccurate, consider timed urine collections for measured creatinine clearance. 2, 3
Common Pitfalls to Avoid
Do not rely on serum creatinine alone without the calculated eGFR—approximately 60% of patients with abnormal renal function by eGFR have normal creatinine values. 3
Never ignore clinical context suggesting altered creatinine generation (extremes of muscle mass, dietary intake, catabolic states), as this leads to systematic errors in GFR estimation. 3
The laboratory must use standardized creatinine assays with calibration traceable to international standards (coefficient of variation <2.3%, bias <3.7%) to ensure accurate eGFR calculation, preferably using enzymatic methods. 1, 3