Understanding Your Comprehensive Metabolic Panel (CMP)

The comprehensive metabolic panel — usually shortened to CMP — is a group of fourteen blood tests that together provide a wide-ranging snapshot of how the body’s most important organ systems are functioning. It includes everything in a basic metabolic panel (BMP) plus six additional measurements that focus on the liver and blood protein levels.

The CMP is one of the most commonly ordered blood test panels in medicine. It is a routine part of annual health checks, pre-operative screening, and the evaluation of patients with abdominal pain, jaundice, fatigue, and many other symptoms. This article explains what each component measures, what abnormal results may mean, and how the additional CMP tests build on the information provided by a BMP.

The reference range that applies to your result is the one printed on your laboratory report, not the typical ranges shown here. Reference ranges vary between laboratories based on the equipment used, the population tested, and individual factors such as age, sex, and pregnancy status. Always compare your result to the reference range printed on your own report, and discuss any abnormal result with your doctor.

What is a comprehensive metabolic panel?

A comprehensive metabolic panel is a group of fourteen measurements performed together on a single blood sample. It includes the eight components of the BMP plus six additional tests:

Components shared with the BMP (covered in detail in our BMP article):

Sodium (Na)
Potassium (K)
Chloride (Cl)
Bicarbonate (CO₂ or HCO₃)
Blood urea nitrogen (BUN)
Creatinine
Glucose
Calcium

Additional components in the CMP:

Albumin — the most abundant protein in the blood
Total protein — the combined amount of albumin and globulin in the blood
Alkaline phosphatase (ALP) — an enzyme found in liver and bone
Alanine aminotransferase (ALT) — an enzyme found mostly in the liver
Aspartate aminotransferase (AST) — an enzyme found in the liver, heart, and muscle
Total bilirubin — a waste product processed by the liver

This article focuses on the six additional components. For details on the eight tests shared with the BMP, see our article Understanding your basic metabolic panel.

Why is a CMP done?

The CMP is ordered for many of the same reasons as a BMP, but with the added ability to assess liver function. Common reasons include:

To investigate symptoms. Jaundice (yellowing of the skin or eyes), abdominal pain, unexplained weight loss, fatigue, and nausea may all prompt a CMP.
To screen for liver disease. The CMP is the standard test for screening for liver problems during routine medical check-ups.
To monitor known liver disease. People with chronic hepatitis, fatty liver disease, cirrhosis, or other liver conditions have CMPs done regularly.
To monitor medications. Many medications can affect the liver, and a CMP is often used to monitor liver function during treatment with drugs such as statins, antibiotics, antifungals, anti-seizure medications, and chemotherapy.
Before surgery and during hospitalization. A CMP is part of routine pre-operative testing and is often repeated during hospital stays.
For routine annual screening. Many doctors include a CMP as part of routine annual health checks.

How is the test performed?

A CMP is performed on a small sample of blood, usually drawn from a vein in the arm. The same blood sample provides results for all fourteen components. The glucose component is affected by recent food intake, so the test may be ordered as a fasting CMP, requiring eight to twelve hours without food. The other components do not require fasting, though some doctors order all CMPs fasting for consistency. Your doctor will tell you whether to fast.

The six additional CMP components

Albumin

Albumin is the most abundant protein in the blood. It is made by the liver and serves several important functions: it helps keep fluid within the blood vessels (rather than leaking into tissues), and it carries hormones, vitamins, and medications through the bloodstream.

A typical reference range for adults is 3.4–5.4 grams per decilitre (g/dL).

Causes of low albumin (hypoalbuminemia):

Severe liver disease, including cirrhosis — the liver loses its ability to make albumin
Kidney disease, particularly nephrotic syndrome, is characterized by the loss of albumin in the urine
Severe inflammation or infection
Malnutrition or malabsorption (such as celiac disease or inflammatory bowel disease)
Burns or other major fluid losses
Heart failure
Pregnancy (a mild decline is normal)

Causes of high albumin:

Dehydration, the most common cause (the albumin appears concentrated in less fluid)
High-protein diet (rare as a sole cause)

Low albumin is more common and clinically meaningful than high albumin. A persistently low albumin level often indicates a serious underlying problem and prompts further investigation.

Total protein

Total protein is the combined amount of all proteins in the blood, primarily albumin and globulin. Globulins are a diverse group of proteins that include antibodies, transport proteins, and clotting factors. Total protein is most useful when interpreted alongside albumin — the difference between the two estimates the globulin level.

A typical reference range for adults is 6.0–7.8 g/dL.

Causes of low total protein:

Severe liver disease
Kidney disease with protein loss in urine
Malnutrition or malabsorption
Severe burns or major fluid losses

Causes of high total protein:

Dehydration
Chronic inflammation, which raises globulin levels
Chronic infection, including HIV and hepatitis
Multiple myeloma and other conditions in which abnormal antibodies are produced

If total protein is high but albumin is normal, the increase is in globulins, which may prompt additional testing such as serum protein electrophoresis to look for an abnormal antibody.

Alkaline phosphatase (ALP)

Alkaline phosphatase is an enzyme found in many tissues throughout the body, but mainly in the liver and bones. ALP enters the blood when these tissues are active or damaged. Because it comes from two main sources, an elevated ALP can reflect either liver or bone disease, and follow-up tests are often needed to determine the source.

A typical reference range varies considerably by age and laboratory. Adult ranges are commonly around 44–147 units per litre (U/L). ALP is naturally higher in growing children and adolescents because of bone growth, and is also higher during the second and third trimesters of pregnancy because the placenta produces ALP.

Causes of high ALP from a liver source:

Bile duct obstruction (gallstones, tumours, or strictures)
Inflammation of the bile ducts (cholangitis)
Some forms of hepatitis
Liver tumours, including liver cancers and metastases
Certain medications

Causes of high ALP from a bone source:

Bone fracture and healing
Paget’s disease of bone
Hyperparathyroidism
Vitamin D deficiency
Bone metastases from cancer
Normal childhood and adolescent growth

Causes of low ALP:

Rare; can occur in malnutrition, severe anemia, or certain genetic conditions

If ALP is elevated, an additional test called gamma-glutamyl transferase (GGT) is often ordered to determine whether the source is liver-related — GGT rises with liver and bile duct problems but not with bone disease.

Alanine aminotransferase (ALT)

Alanine aminotransferase is an enzyme found mostly inside liver cells. When liver cells are injured or destroyed, ALT leaks out into the bloodstream, raising blood levels. Of all the tests in a CMP, ALT is the most specific for liver injury, which makes it one of the most clinically useful liver tests.

A typical reference range for adults is 7–56 U/L, though ranges vary by laboratory and may be slightly higher in men than in women.

Causes of high ALT:

Viral hepatitis (hepatitis A, B, or C)
Alcohol-related liver disease
Non-alcoholic fatty liver disease (NAFLD), now the most common cause of mildly elevated ALT in many populations
Medication-induced liver injury (acetaminophen overdose, statins, antibiotics, anti-seizure medications, herbal supplements, and many others)
Autoimmune hepatitis
Hereditary liver conditions such as hemochromatosis and Wilson disease
Liver tumours, including liver cancer and metastases
Strenuous exercise (a mild and temporary increase)

Causes of low ALT:

Rare and not usually clinically significant
Can occur in chronic kidney disease and vitamin B6 deficiency

The pattern of how high ALT rises and how it compares to AST helps narrow down the cause. A sudden, very high ALT (sometimes more than 1000 U/L) suggests acute viral hepatitis, drug toxicity, or severe liver injury. Mildly elevated ALT that is persistent often suggests fatty liver disease or chronic viral hepatitis.

Aspartate aminotransferase (AST)

Aspartate aminotransferase is an enzyme found in the liver, heart, skeletal muscle, kidneys, and red blood cells. Like ALT, it leaks into the blood when its parent cells are damaged. Because AST comes from multiple tissues, an elevated AST is less specific for liver disease than ALT — it can also reflect heart attack, muscle injury, or red blood cell breakdown.

A typical reference range for adults is approximately 10–40 U/L.

Causes of high AST:

The same liver causes as ALT (viral hepatitis, alcohol, NAFLD, medications, and others)
Heart attack, although troponin is now the preferred cardiac test
Skeletal muscle injury, including rhabdomyolysis and after strenuous exercise
Red blood cell destruction (hemolysis)
Some thyroid conditions

The AST:ALT ratio can suggest specific causes:

An AST:ALT ratio greater than 2 in someone with elevated liver enzymes is a classic sign of alcohol-related liver disease
An AST:ALT ratio less than 1 (i.e., ALT higher than AST) is more typical of viral hepatitis or fatty liver disease
A very high AST without elevated ALT may suggest a non-liver source such as muscle injury

Total bilirubin

Bilirubin is a yellow-orange waste product produced when red blood cells are broken down. The liver processes bilirubin and excretes it into the bile, which then flows into the intestines and out of the body. Bilirubin builds up in the blood when red blood cells are being destroyed faster than the liver can clear them, when the liver is not working properly, or when the bile ducts are blocked.

A typical reference range for total bilirubin in adults is approximately 0.1–1.2 mg/dL.

When bilirubin levels rise significantly, it can cause jaundice — a yellow tint to the skin and the whites of the eyes. Jaundice typically becomes visible when total bilirubin exceeds about 2.5–3.0 mg/dL.

Causes of high bilirubin:

Liver disease, including hepatitis and cirrhosis
Bile duct obstruction (gallstones, tumours, or strictures)
Hemolysis (rapid breakdown of red blood cells)
Gilbert syndrome, a common and harmless inherited condition that causes mild bilirubin elevations, particularly during fasting or stress
Newborn jaundice in infants (particularly common and usually resolves on its own)
Certain medications

Most laboratories also offer separate measurements of direct (conjugated) bilirubin and indirect (unconjugated) bilirubin. The pattern helps determine the cause: high indirect bilirubin suggests problems before the liver processes it (such as red blood cell breakdown or Gilbert syndrome), while high direct bilirubin suggests problems with the liver itself or the bile ducts. These additional measurements are not part of the routine CMP but may be ordered as follow-up.

Patterns of liver test abnormalities

The four liver-related tests in the CMP — ALP, ALT, AST, and total bilirubin — are most useful when interpreted together as a pattern rather than individually. Three common patterns are:

Hepatocellular pattern. ALT and AST are elevated, with ALP and bilirubin normal or only mildly elevated. This pattern points to direct injury of the liver cells themselves and suggests causes such as viral hepatitis, fatty liver disease, alcohol-related liver injury, or medication toxicity.
Cholestatic pattern. ALP and bilirubin are elevated, with ALT and AST normal or only mildly elevated. This pattern points to problems with bile flow and suggests causes such as bile duct obstruction (often from gallstones), primary biliary cholangitis, or some medication reactions.
Mixed pattern. Both groups are elevated. This pattern is non-specific and may need additional investigation to clarify the cause.

Your doctor will look at the overall pattern, the magnitude of any elevations, and the trend over time before deciding what further investigation, if any, is needed. For a more detailed discussion of liver tests including additional tests beyond the CMP (such as GGT, LDH, and prothrombin time), see our Understanding your liver panel article.

What happens after a CMP?

If your CMP results are within reference ranges, no further investigation is usually needed. If a result is abnormal, the next steps depend on which measurement is abnormal, by how much, and what other findings are present. Some possibilities include:

Repeat the test. Mildly abnormal liver enzymes often resolve on their own or vary from day to day. A repeat test in a few weeks can confirm whether the abnormality is real and persistent.
Add additional liver tests. Persistently elevated liver enzymes typically prompt additional testing for viral hepatitis, autoimmune liver disease, iron studies (for hemochromatosis), and an abdominal ultrasound to look for fatty liver, gallstones, or other structural problems.
Add other organ-specific testing. An elevated ALP without an obvious liver cause may prompt bone-related testing. A high total bilirubin with otherwise normal liver tests may prompt testing for hemolysis or for Gilbert syndrome.
Adjust medications. If a medication is suspected as the cause of liver enzyme elevations, your doctor may stop or change the medication and recheck enzymes after a few weeks.
Refer to a specialist. Persistent or significant liver test abnormalities may prompt referral to a hepatologist (liver specialist) or a gastroenterologist.
Order imaging. Liver ultrasound, CT, or MRI may be ordered to look at the liver and bile ducts directly.
Consider a liver biopsy. In some cases, particularly when the cause of persistent liver test abnormalities cannot be determined by blood tests and imaging, a liver biopsy may be needed.

An abnormal CMP result is a starting point. Your doctor will interpret the results in the context of your symptoms, medical history, medications, alcohol use, and any other test results before deciding whether further investigation is warranted.

Questions to ask your doctor

Were any of my CMP results outside the reference range?
If a liver enzyme is elevated, how significant is the elevation?
What is the most likely cause given my history and medications?
Could any of my medications, supplements, or alcohol intake be contributing?
Should the test be repeated, and if so, when?
Do I need additional liver tests, hepatitis testing, or imaging?
Should I be referred to a hepatologist or gastroenterologist?
Are there changes I can make to my diet, weight, alcohol use, or medications that would improve my results?