Components of a Comprehensive Metabolic Panel and Liver Function Testing
A Comprehensive Metabolic Panel (CMP) includes some but not all components of liver function testing, making it insufficient for complete liver function assessment.
What a CMP Includes
- A standard CMP includes basic liver enzymes: ALT, AST, ALP, bilirubin, albumin, and total protein 1
- These components provide information about hepatocellular injury (ALT, AST) and some aspects of synthetic function (albumin) 2, 1
- Bilirubin in the CMP measures the liver's ability to process waste products 1
What a CMP Lacks for Complete Liver Function Assessment
- GGT (gamma-glutamyl transferase) is not included in a standard CMP but is recommended in initial liver function testing to increase sensitivity for detecting alcohol-related and non-alcoholic fatty liver disease 2, 1
- Prothrombin time (PT) and INR, which are critical markers of liver synthetic function, are not part of a CMP 2, 1
- Platelet count, which can indicate advanced liver fibrosis, is part of a complete blood count (CBC), not a CMP 2
Comprehensive Liver Function Assessment
- The British Society of Gastroenterology recommends that initial investigation for potential liver disease should include bilirubin, albumin, ALT, ALP and GGT, together with a full blood count 2, 1
- The AST:ALT ratio is valuable for assessing fibrosis risk, with a ratio >1 suggesting advanced fibrosis/cirrhosis 2, 1
- For true synthetic function assessment, PT/INR should be included alongside the CMP parameters 2, 1
Clinical Implications
- Relying solely on a CMP for liver function assessment may miss important indicators of liver disease, particularly in alcohol-related and non-alcoholic fatty liver disease 2, 1
- Normal liver tests, including those in a CMP, do not exclude significant liver disease 1, 3
- For patients with suspected liver disease, a more comprehensive panel beyond the CMP is necessary 1
When Additional Testing Beyond CMP is Needed
- When evaluating patients with risk factors for liver disease (alcohol use, metabolic syndrome, viral hepatitis risk) 2, 1
- When monitoring known liver conditions 1
- When initial CMP results show abnormalities that require further investigation 1
- For high-risk patients, consider simultaneous second-line testing rather than sequential testing 1
Cost-Effective Approach
- Consider "reflex" testing where additional tests like GGT are automatically performed on the same sample if initial CMP tests are abnormal 1
- For routine screening in low-risk patients, a CMP may be sufficient as an initial test, with follow-up testing if abnormalities are detected 4
Remember that liver function involves multiple complex processes, and no single test or panel can comprehensively assess all aspects of liver function 3. When comprehensive liver function assessment is needed, additional testing beyond the standard CMP is necessary.