When to Order BMP vs. CMP
Order a BMP when you need only kidney function, electrolytes, and glucose monitoring; order a CMP when liver function assessment is also required. 1
Clinical Decision Framework
Order a BMP for:
Routine electrolyte and kidney function monitoring in patients with diabetes, chronic kidney disease, or those on diuretics where liver assessment is not indicated 1
Follow-up monitoring of known metabolic conditions when liver function has been previously assessed and is stable 2
Acute care settings where rapid assessment of electrolytes, renal function, and glucose is needed without liver concerns 3
Cost-conscious care when liver function tests are not clinically indicated, as BMPs cost approximately $21 less than CMPs 3
Order a CMP when:
Right upper quadrant pain, jaundice, hepatomegaly, or ascites are present 3
Suspected liver disease, overdose, or malignancy requiring comprehensive metabolic assessment 3
Heart disease or bleeding disorders where liver synthetic function assessment is relevant 3
Initial cancer workup including renal cell carcinoma and myeloproliferative neoplasms 1
Obesity assessment requiring comprehensive metabolic and liver function evaluation 1
Tumor lysis syndrome risk where comprehensive metabolic monitoring including liver function is needed 1, 4
Acute stroke evaluation where underlying liver conditions may influence management 1
NAFLD screening in high-risk patients 1
Key Clinical Variables Predicting Need for CMP
The presence of any of these 12 clinical variables justifies ordering a CMP over a BMP: 3
- History of liver disease (strongest predictor, P = 0.007) 3
- History of heart disease (P = 0.040) 3
- Jaundice (P = 0.045) 3
- Hepatomegaly (P = 0.048) 3
- Right upper quadrant pain or tenderness 3
- Overdose 3
- Malignancy 3
- Bleeding disorder 3
- Ascites or peripheral edema 3
- Shock 3
- Emesis (persistent) 3
In the absence of all 12 variables, a BMP is sufficient and avoids unnecessary testing. 3
Important Caveats
Avoid Reflexive CMP Ordering
Implementation of routine CMP ordering increased total calcium testing by over 3-fold without changing the rate of calcium-related diagnoses (1.29% vs 1.27%), suggesting substantial unnecessary testing 5
Only 1.4% of preoperative CMPs and 1.5% of postoperative CMPs were actionable in surgical patients, indicating most routine comprehensive panels do not alter management 6
The false-negative rate for missing liver abnormalities with BMP-only ordering is 16%, but these missed values are typically marginally abnormal and rarely prompt further investigation 3
Cost and Resource Considerations
Limiting testing to BMP in patients without the 12 clinical variables can save approximately $7,125 annually in a single pediatric emergency department 3
A 20% reduction in total labs ordered was achieved through mindful ordering practices that emphasized BMP over CMP when liver assessment was not indicated 2
Multifaceted interventions reducing unnecessary CMP ordering decreased laboratory costs from $138 to $123 per day without increasing length of stay or readmissions 7
Practical Implementation
Start with these questions before ordering:
- Is there any clinical suspicion for liver disease based on the 12 variables above? If yes → CMP 3
- Is this initial evaluation of a complex condition (cancer, metabolic disorder, obesity)? If yes → CMP 1
- Is this routine monitoring of known kidney disease, diabetes, or electrolyte disorders? If yes → BMP 1
- Has liver function been recently assessed and is stable? If yes → BMP 2
This algorithmic approach maximizes diagnostic yield while minimizing unnecessary testing and costs. 3, 2