Does CMP Include HgB A1c?
No, a Comprehensive Metabolic Panel (CMP) does not include Hemoglobin A1c (HgB A1c). These are separate laboratory tests that must be ordered independently.
What is Included in a CMP
A CMP is a standard chemistry panel that measures the following components 1:
- Electrolytes: Sodium, potassium, chloride, carbon dioxide (bicarbonate)
- Kidney function markers: Blood urea nitrogen (BUN), creatinine
- Liver function tests: Aspartate aminotransferase (AST), alanine aminotransferase (ALT), alkaline phosphatase (ALP), bilirubin, albumin, total protein
- Metabolic markers: Glucose (single point-in-time measurement), calcium
The CMP provides only a single snapshot glucose value at the time of blood draw, which reflects immediate blood sugar levels 1.
What is HgB A1c and Why It's Separate
HgB A1c is a distinct test that reflects average glycemia over the preceding 2-3 months and must be specifically ordered 1. Key characteristics include:
- Measures glycated hemoglobin, which forms when glucose attaches to hemoglobin in red blood cells 1
- Requires specialized laboratory methods certified by the National Glycohemoglobin Standardization Program (NGSP) and standardized to the Diabetes Control and Complications Trial (DCCT) assay 2
- Used for both diagnosis and monitoring of diabetes, with testing recommended at least twice yearly for stable patients and quarterly for those not meeting glycemic goals 1, 2
Clinical Implications
When evaluating diabetes or glycemic control, you must order both tests separately 1:
- Order a CMP to assess current metabolic status, kidney function, liver function, and electrolytes
- Order HgB A1c separately to assess long-term glycemic control over the past 2-3 months 1, 2
The single glucose value in a CMP cannot substitute for HgB A1c because it only captures one moment in time and does not reflect average glycemic control or predict diabetes complications 1.
Common Pitfall to Avoid
Do not assume that the glucose value in a CMP provides adequate information about glycemic control. A normal fasting glucose on a CMP does not rule out diabetes or poor glycemic control, as HgB A1c may still be elevated 1. Conversely, an elevated random glucose on a CMP requires confirmation with proper diagnostic testing including HgB A1c 2.