A comprehensive metabolic panel (CMP) is a group of blood tests that provide your doctor with information about your overall health and metabolism. Read on to learn about what doctors look for, how to prepare for the test, and what your results mean.
What is a Comprehensive Metabolic Panel (CMP)?
A comprehensive metabolic panel (CMP), or chemical screen, is a panel of 14 blood tests commonly ordered by doctors to screen for health issues during yearly physical exams. A CMP provides a rough overview of:
- Kidney and liver function
- Blood sugar (glucose) levels
- Electrolyte and acid/base fluid balance
- The amount of proteins in the blood
This test is also regularly used to monitor disease progression in patients with diabetes or high blood pressure, as well as liver and kidney damage in patients taking certain medications (e.g., acetaminophen, statins, opioids, antibiotics).
How is the CMP Different from the BMP?
The CMP is an expanded version of the basic metabolic panel (BMP). The BMP consists of only 8 tests (not including liver or protein tests) [1].
While both tests provide a broad screen of overall health and metabolism, a doctor may order a CMP instead of a BMP to get a more complete picture of a person’s organ function or to check for specific conditions, such as diabetes, liver or kidney disease.
What is Included in a CMP Blood Test?
- Albumin
- Carbon Dioxide (Bicarbonate)
- Calcium
- Potassium
- Sodium
- Chloride
- Blood Urea Nitrogen (BUN)
- Creatinine
- Glucose
- Total Bilirubin
- Total Protein
- Alanine Aminotransferase (ALT)
- Alkaline Phosphatase (ALP)
- Aspartate Aminotransferase (AST)
Glucose Test
Glucose is the body’s main source of energy. It’s produced during the breakdown of carbohydrates. Glucose levels typically rise after a meal and then decrease over time. If blood glucose levels remain consistently high, they can cause eye, kidney, nerve, and blood vessel damage [2].
Testing the level of glucose in the blood is one of the best ways to help diagnose or monitor prediabetes and diabetes [3].
Kidney Function Tests
Kidney function tests are done to determine the overall health of the kidneys, diagnose and manage conditions affecting kidney function, screen people at risk of developing kidney disease, or monitor patients with kidney disease [4].
Creatinine Test
Creatinine is a waste product found in the blood and urine. It is a product of the normal wear and tear of muscles [5].
Kidneys filter creatinine from the blood into the urine at a fairly constant rate. When kidneys aren’t working properly, less of creatinine is filtered into urine and blood levels increase. That’s why blood levels can be used as an indication of kidney function [6, 5].
Blood Urea Nitrogen (BUN)/Urea Test
Like creatinine, urea is a waste product that is tested to gauge kidney function [5].
Urea is produced in the breakdown of proteins in the body. When the kidneys are not filtering toxins out properly, urea can accumulate in the blood [7, 5].
However, BUN is a less reliable indicator of kidney function than creatinine because it is far more likely to be affected by other factors, including diet, dehydration, and exercise [5].
Kidney function can also be determined by looking at BUN and creatinine together. This is called the BUN/creatinine ratio [5].
Proteins
Proteins are building blocks of all cells and tissues. They are necessary for growth, development, and overall health and wellbeing [8].
Normally, protein levels in the blood are relatively stable, reflecting a balance between protein loss and production. This balance can be disrupted in certain conditions, such as kidney disease, heart failure, or inflammation, resulting in high or low protein levels in the blood [9].
Albumin Test
Albumin is a protein made in the liver. One of its main functions is to keep fluids inside of blood vessels and maintain blood volume. Albumin also helps transport hormones, vitamins, drugs, fatty acids, minerals, and other substances by binding them in the blood and delivering them to tissues [10, 11].
Low levels of albumin in the blood may indicate inflammation, liver disease, or other health issues, such as malnutrition [12, 13, 9].
Globulin Test
Globulins are a group of proteins in the blood that help transport nutrients and fight infections [9].
Globulin proteins can be enzymes, antibodies, transport proteins, and others [9].
Some globulins are made in the liver, while others are made by the immune system [9].
Lower than normal globulin levels may indicate liver or kidney disease, while higher levels may be a sign of infection or a bone marrow disorder [9, 14].
Total Protein Test
The total protein test measures the total amount of albumin and globulin in your blood [9].
Normally, albumin makes up more than half of blood proteins, and the remainder of the protein count is the total globulins [9].
Total blood protein is used to check for nutritional deficiencies, digestive problems, and dehydration. It is also used to help evaluate liver and kidney function [9].
Liver Function Tests
Liver function tests help assess how well the liver is working.
When the liver is not functioning properly, levels of various enzymes, proteins, and other substances in the blood may rise or fall. Elevated liver enzyme levels may be a sign of liver damage caused by infection (e.g., viral hepatitis), disease, excessive alcohol consumption, or drug toxicity [15].
Alanine Aminotransferase (ALT)
ALT is an enzyme involved in the breakdown of proteins for energy in the body. It is mainly found in the liver, but also in smaller amounts in the kidney, heart, muscles, fat tissue, intestines, and pancreas [16].
Normally, ALT levels in the blood are low. However, when the liver is damaged, ALT is released into the bloodstream [16].
An ALT test is done to monitor liver health and determine if the liver is damaged (from drugs or disease) [16].
Aspartate Aminotransferase (AST)
AST is another enzyme involved in the breakdown of proteins for energy. It is mainly found in the liver and heart, and in smaller amounts in the pancreas, kidneys, and muscles. Damage to any one of these tissues increases AST release into the blood [17, 18].
AST levels are measured in liver function tests to help determine overall liver health. But since increases in AST levels can also indicate damage to other organs (i.e., heart, kidneys, muscle tissue), AST is often paired with additional tests. This helps doctors with the diagnosis [19].
Alkaline Phosphatase (ALP)
Alkaline phosphatase is an enzyme found in all tissues in the body but is mostly concentrated in the bones, kidneys, liver, intestines, and placenta. It exists in different forms, depending on its origin [20].
Its major function is to protect your intestinal tract against bacteria, aid in digestion, break down fats and some B vitamins, and promote bone formation [20].
Higher than normal blood ALP levels may indicate bone, bile duct, or liver disorders [21].
Bilirubin
Bilirubin is a yellow pigment that is produced by the normal breakdown of hemoglobin from red blood cells [22].
Before bilirubin can get removed from the body, it has to be first processed by the liver. In the liver, bilirubin attaches to sugars, becoming water-soluble, and is then removed via the gallbladder [23].
Bilirubin levels may be elevated in people with severe liver disease, gallbladder disease, or other bile duct diseases that impair bile flow. Elevated bilirubin levels can also result from conditions that increase the destruction of red blood cells (i.e., internal hemorrhage and certain hemolytic anemias) [23].
Electrolytes
Electrolytes are minerals that carry an electric charge (ions) when they are dissolved in fluids such as blood. Sodium, potassium, chloride, and bicarbonate are blood electrolytes that are essential for nerve and muscle function, blood pressure control, acid-base and water balance in the body [24].
The kidneys (and hormones) help maintain electrolyte levels by filtering electrolytes and water from the blood: they recycle what’s needed back into the blood and excrete what isn’t into the urine [24, 25, 26].
If the electrolyte balance is disturbed and left untreated, serious problems can occur, such as coma, seizures, and heart attack (cardiac arrest) [27, 26, 28].
Sodium
Sodium is an essential mineral and electrolyte that helps maintain normal fluid and acid-base balance in the body. It is also important for ensuring that neurons and muscles communicate effectively [24].
Most of the body’s sodium is found in the blood and in the fluid around cells [24].
Healthy kidneys maintain a constant level of sodium in the body by adjusting the amount that gets excreted in the urine. Sodium imbalances may indicate a problem affecting the kidneys, dehydration, or an underlying medical condition (such as Addison’s disease) [29].
Potassium
Potassium has a variety of functions. It helps [30, 31, 32, 33, 34, 32]:
- balance fluids
- facilitate nerve and muscle communication
- control blood pressure
- store nutrients (including glucose) inside cells
Unlike sodium, which is found mainly outside the cells, most of the potassium in the body is located inside the cells [35].
Normally, the kidneys maintain potassium levels in the blood within a narrow range. When blood potassium levels are too high or too low, serious problems can occur, such as an abnormal heart rhythm or a heart attack (cardiac arrest) [36, 35, 37].
A potassium blood test is important for evaluating heart, kidney, adrenal gland, muscle, and digestive system function [35].
Carbon Dioxide (CO2)/Bicarbonate
CO2 is a waste product of the body’s metabolism. Most of the CO2 in the blood is in the form of bicarbonate (HCO3-) [38].
The lungs and kidneys help maintain blood pH by controlling the amount of bicarbonate in the blood. This balance is critical because even minor deviations from the normal range can severely affect the brain, heart, arteries, muscles, and other organs. Conditions that affect the lungs, kidneys, and metabolism can cause acidosis (low pH) or alkalosis (high pH) [38].
Measuring the levels of bicarbonate in the blood can help uncover the body’s acid-base balance disturbances and diagnose electrolyte imbalances [38].
Calcium
Calcium is the most abundant mineral in the body. It is vital for muscle contractions, nerve impulse transmission, enzyme function, normal heart rhythm, blood clotting, cell division, and forming/maintaining healthy bones and teeth [39].
Nearly 99% of the body’s calcium is stored in the bones. The remaining 1% is found in the blood [40].
Calcium levels are tightly controlled by the parathyroid hormone and vitamin D. If blood levels drop, bone cells release calcium to maintain blood concentrations [40].
Calcium levels that are too low or too high may signal bone disease, thyroid disease, kidney disease, or other medical conditions [41].
Chloride
Chloride is an electrolyte. It’s essential for maintaining the acid-base (pH) and fluid balance in the body. It’s also needed for transmitting nerve impulses [42].
In general, chloride levels mirror sodium levels, meaning that when sodium levels are high, chloride levels are also high. However, if there is an acid-base (pH) imbalance in the body, chloride levels may change independently of sodium [42, 43].
Since the kidneys play an important role in controlling chloride levels in your body, a chloride imbalance may point to a kidney problem. Abnormal chloride may also be caused by other conditions, like diabetes or severe dehydration, which can affect the ability of the kidneys to maintain chloride balance [42].
General Testing Information
When Should You Get Tested?
The CMP is usually requested as part of a blood work-up for a yearly physical or medical exam.
Your doctor may also order a CMP when you have diabetes, high blood pressure, liver or kidney disease, or are taking medications that may impact your kidney or liver.
How is the Sample Collected for Testing?
A blood sample is obtained by inserting a needle into a vein in the arm. Blood is drawn through the needle into a tube and analyzed in a lab.
How to Prepare for a CMP Blood Test
To make sure your CMP results are as accurate as possible, you should not eat or drink for 8 to 12 hours before the test. Basically, it is best to do this test in the morning, before breakfast.
What Do Your CMP Blood Test Results Mean?
Doctors will usually evaluate individual tests together to look for patterns. A single abnormal test result may or may not have any medical significance if all other tests are normal. For example, a high result of just one of the liver enzyme tests has different implications than high results of several liver enzyme tests.
Results are also interpreted within the context of previous tests you have had done as well as other factors, including your medical history and physical exam.
Occasionally, especially in hospitalized patients, several sets of CMPs are performed on different days to get more information about the underlying condition and how it responds to medical treatment.
Abnormal results can be due to a variety of different medical conditions. An out of range result can be followed up with one or more specific tests to pinpoint the cause and/or decide on a treatment.
Limitations and Caveats
While the individual tests of the CMP are sensitive, they may not reveal a specific problem. For this reason, abnormal test results are usually followed up with additional tests to confirm or rule out a suspected diagnosis.
Sometimes, the results of a CMP test come back abnormal, even though nothing is wrong. That is because many factors can affect a CMP, including:
- Medication (i.e, insulin, Tylenol/acetaminophen, hormones)
- Eating or drinking before the test
- Exercising before the test
Be sure to tell your doctor about any medications you are taking. Likewise, it is important to provide a complete history of your health as many other factors can also affect the interpretation of your results.
