There are several common blood tests that healthcare providers use to gain a quick assessment of patient health and detect potential issues. These include the complete blood count (CBC), the basic metabolic panel (BMP), and the comprehensive metabolic panel (CMP). This article summarizes these most common blood tests, approximate normal ranges, and the common causes of out-of-range results, with a special emphasis on the health of people with diabetes.
The normal reference range provided below may vary slightly depending on the specific laboratory and may also vary slightly depending on age, sex, race, and pregnancy status. It is crucial to work with your healthcare provider to fully understand what each lab result means for your individual situation. Your physician will look at your overall health status and consider any medications you take, as well as your lab work trends over time to make the most appropriate recommendations.
A complete blood count (CBC) provides an important overview of your health and can reveal a variety of potential issues, ranging from dehydration or dietary deficiency to potentially more serious ones like infections and cancer, among others. Let’s review the different cell types and other important components that are found in our blood and what elevated or low levels may indicate.
Complete Blood Count (CBC)
There are many different types of white blood cells, namely: neutrophils, lymphocytes, monocytes, eosinophils, and basophils, which all work together to combat infections. A lower than normal WBC count may occur for several reasons, including use of certain medications (e.g., some antibiotics), an autoimmune condition (including lupus and rheumatoid arthritis), issues with the bone marrow or spleen (both produce white blood cells), or certain types of cancer. Lack of specific nutrients (like B vitamins) could also be responsible for a low count. A higher than normal WBC count usually indicates an ongoing infection, as the body increases the production of its defenses. Less frequently, a high WBC count may be indicative of leukemia or a bone marrow disorder. In addition, some medications may result in higher WBC production. In case of an abnormal result, looking at the specific distribution of all specific WBC types may help identify the likely cause.
Red blood cells (RBCs), also called erythrocytes, are specialized flat-shaped cells that distribute oxygen through the body. A protein called hemoglobin (see below) is abundant in these cells and can bind to and release oxygen. A lower than normal RBC count is called anemia and may indicate blood loss, a nutritional deficiency, or certain bone marrow disorders. Sometimes, a low count may indicate chronic kidney disease or a rare inflammatory health condition that could cause premature cell destruction. Higher than normal levels of RBC counts could also be due to dehydration. More rarely, it could signify a rare genetic health condition, kidney tumors, or lung disease.
University of Minnesota Physicians and University of Minnesota Medical Center. Created for the National Cancer Institute.
Hemoglobin (HgB) is the protein in RBCs that binds to oxygen and delivers it to the tissues that need it. As with lower RBC counts, lower than normal levels of hemoglobin are termed anemia. Often, low hemoglobin levels signify an iron deficiency and can also be a result of excess bleeding. Higher than typical hemoglobin levels may be a compensation mechanism for poor lung function, or could be normal in certain cases, such as for people who live at higher altitudes. Less frequently, high hemoglobin levels arise from a bone marrow disorder or from taking certain medications.
Hematocrit (HcT) is defined as the ratio of red blood cells to the total volume of plasma. Lower than normal levels may indicate anemia, blood loss, nutritional deficiency, or an infection (thus raising the % of WBCs and resulting in a lower % of RBCs). Higher than normal levels are often due to dehydration but could also be due to some lung and heart conditions.
Mean corpuscle volume (MCV) is an estimate of the average size of RBC. Lower than expected levels are often due to anemia or blood loss. Larger than expected values may be indicative of a B vitamin deficiency.
Platelets (Plt), named for their plate-like shape, are very specialized cells that promote blood clotting, thereby preventing blood loss. Lower than normal platelet levels could be due to numerous causes, including taking certain medications, some rare genetic disorders, and some forms of cancer (e.g., leukemias and lymphomas). Alcohol abuse and kidney problems could also be the culprit. Higher than normal platelet levels could be related to bone marrow issues, but could also arise from another issue, like anemia, infection, and certain types of cancer.
Mean platelet volume (MPV) is an estimate of the average size of the platelets. Larger than normal platelet size is associated with a low platelet count but can also be a sign of blood cancer, cardiovascular disease, and is a hallmark of pre-eclampsia in pregnant women. Smaller than normal platelet size may result from certain medications and in some cases, from bone marrow disorders.
The basic metabolic panel (BMP) provides an overview of electrolytes and a few other key substances in the blood and can be used to diagnose metabolic disorders (e.g., diabetes) and to screen for kidney disease.
Electrolytes are charged particles that serve many functions in the body. The major electrolytes include sodium, potassium, chloride, calcium, bicarbonate, and phosphate. Some of their most important roles include regulating electrical impulses in the brain and muscles, stimulating the appropriate release of hormones from various glands, maintaining blood pressure and fluid balance throughout the body, and much more.
So, it is not surprising that one of the most basic blood tests, the BMP, focuses primarily on assessing the levels of these molecules. Let’s dig deeper into this test and learn what a low or high result may mean.
Basic Metabolic Panel (BMP)
Low sodium levels may be due to kidney function problems, medications that increase urination (diuretics), or dehydration (such as from diarrhea, vomiting, etc.). Higher levels of sodium may be a symptom of Cushing’s disease, a condition characterized by the overproduction of cortisol by the adrenal glands. It could also be a result of dehydration.
Low potassium may be a result of dehydration, but could also be due to dietary deficiency, alcohol abuse, or indicate an adrenal gland issue, like Cushing’s disease. Higher than normal potassium levels can have many causes, including kidney problems, Addison’s disease, injury, and certain medications (i.e., some diuretics and antibiotics). It can also present during diabetic ketoacidosis (DKA) in patients with diabetes.
The balance of sodium and potassium inside vs. outside cells is critical for correct cellular function. Fluid balance illustration by Christine Dobrowolski, CC BY-NC-SA 4.0.
Low levels of chloride may be due to kidney problems and in some cases, may be due to acidosis. Vomiting or diarrhea can also cause low chloride levels. Higher than normal chloride levels may indicate dehydration or high sodium intake. However, it could also be due to heart disease and certain lung conditions, like cystic fibrosis.
Low levels of calcium may be due to parathyroid gland dysfunction or low vitamin D status. A higher than normal level may be due to overactive parathyroid gland, or a very high intake of vitamin D. High levels may increase the risk for developing kidney stones.
Low levels of bicarbonate may indicate kidney issues or acidosis (including DKA). It may also be due to poisoning (e.g., aspirin, antifreeze) or may present due to Addison’s disease. Higher than normal levels may be a result of dehydration but can also arise in patients with certain lung conditions, and in those with anorexia, as well as adrenal gland disorders, like Cushing’s syndrome.
Blood urea nitrogen (BUN) is a waste product produced by the liver that is then removed by the kidneys; however, if the kidneys are not functioning properly, the levels of this substance in the blood may rise. A lower than expected result could indicate liver disease, or a nutritional deficiency (low-protein diet). Also, too much water intake could cause an artificially low result.
Creatinine is a metabolite of creatine, a substance that is abundant in muscle cells. Creatinine is excreted as a waste product by the kidneys. Lower than normal levels of creatinine in the blood may point to a muscle disorder, liver disease, or could be due to a diet that is very low in protein. Also, pregnant women may sometimes have lower blood creatinine levels. A higher than normal creatinine level is often a red flag for kidney disease (as the waste product builds up in the bloodstream due to ineffective clearance by the kidneys). This could also be a temporary effect of dehydration, a very high protein diet, or from using certain medications.
Higher than normal blood glucose levels usually indicate diabetes or pre-diabetes, but could also be a temporary occurrence due to a stress response or illness, or from certain medication, like corticosteroids. A hemoglobin A1c test can be performed to reveal the average blood glucose levels over the course of several months. In people who are being treated for diabetes, lower than normal blood glucose levels are usually due to too much insulin or another blood glucose-lowering medication. In those without diabetes, low blood glucose levels may be due to long periods of fasting or excessive alcohol use. Sometimes, this could indicate insulin overproduction due to a tumor in the pancreas (insulinoma), or issues with adrenal and/or pituitary glands.
A comprehensive metabolic panel (CMP) includes all the tests performed in the BMP (see above), but also usually assesses the following components:
Additional parameters are evaluated as part of the comprehensive metabolic panel (CMP). *Read about the estimated glomerular filtration rate (EGFR) and anion gap below.
Proteins are the workhorses of the body and perform an array of important functions. In fact, the human body is approximately 16% protein. Higher than normal values may be due to dehydration, certain infections (e.g., hepatitis C), and some cancers. Lower than normal protein levels in the blood can have various causes, including dietary deficiency, certain autoimmune conditions that affect the GI tract, as well as liver or kidney disease (as protein is lost through the kidneys via urine).
Illustration of the makeup of the human body. Youst / Getty Images
Albumin is an abundant protein (~60% of total protein) that is produced by the liver. It can bind to many natural and foreign substances in the body and transport them. A lower than normal level of albumin in the blood could be due to kidney or liver disease. Another possibility is dietary deficiency of protein, over time, or due to fasting. A higher than expected level of albumin in the blood is often an artifact of dehydration, or sometimes caused by a very high-protein diet.
In addition to albumin (see above), globulin proteins make up the remaining ~40% protein in the blood. Globulins are produced by the immune system and the liver and play a central role in fighting off infection. Higher than normal globulin levels may be due to an ongoing infection or immune system disorder. It could also be a result of dehydration, from using certain medications, and in some cases, due to certain cancers. Low levels of globulin could indicate liver or kidney disease.
ALP is a protein that helps to break down other proteins, and is mainly present in the liver, kidneys, and bones. Lower that normal ALP levels may be due to a dietary deficiency (e.g., zinc) and very rarely a genetic bone development condition. Certain medications, like some oral contraceptives may cause lower levels of ALP. Higher than normal ALP levels may signify liver disease. Sometimes, levels can be transiently elevated during pregnancy (especially in the third trimester) or in growing children: this is generally a normal occurrence in these cases.
ALT is a protein that is released into the bloodstream when cells are damaged. Too high levels of ALT may indicate liver damage. Some medications (e.g., statins) may cause higher ALT levels. In general, it is normal for ALT levels to be low and very low levels are generally not a cause for concern; however, very low levels may be a marker of older age and frailty, and some research suggests that this may be a risk factor for mortality in some patient populations.
AST is a protein typically found in the liver and muscles and is released into the blood when there is liver damage. Thus, a higher than normal reading is often indicative of liver problems or could also be related to pancreatitis or cardiovascular problems. Some medications (e.g., statins) may cause higher than normal AST levels. As with ALT, low levels of AST are not generally a cause for concern.
Bilirubin is produced when red blood cells are broken down and is cleared via the liver. Elevated levels of bilirubin in the blood may signify liver disease. In general, lower than expected levels of bilirubin are not a cause for concern and may be due to caffeine intake and the use of certain drugs (e.g., NSAIDs).
EGFR is a value that is calculated based on the creatinine levels in your blood (see above) and it also takes the patient’s age, sex, and race into account. This measure is a hallmark for evaluating kidney function (see chart below).
Image credit: American Kidney Fund
The anion gap is a calculated value typically obtained by subtracting the concentration of the chloride AND bicarbonate from the sodium concentration in the blood. It is a measure of the electrolyte balance in the body and is related to the acid/base balance (pH). A lower than normal anion gap value may be due to low albumin levels in the bloodstream (e.g., due to kidney or cardiovascular disease), and sometimes, certain cancers. A higher than normal value is indicative of acidosis and is often due to an underlying condition, such as diabetes (DKA). Metabolic acidosis can also arise from dehydration, alcohol abuse, and certain medications.
The blood tests discussed above (CBC, BMP, and CMP) are some of the most common laboratory blood tests that can help to reveal a variety of potential health issues. Numerous other in-depth tests may be performed to pinpoint health problems, depending on a patient’s specific health history and symptoms.
For example, for people with diabetes, urinalysis if often performed to look for any early signs of kidney damage (such as protein spilling into the urine, also known as microalbuminuria), or to rule our bladder or kidney infections. People with type 1 diabetes usually undergo regular tests to check their thyroid function, as autoimmune conditions, such as type 1 diabetes and thyroid disease often co-present. Also, the hemoglobin A1c test provides an estimate of blood glucose over several months and is a hallmark of assessing blood sugar management in people with diabetes. It is typically performed every 3-6 months. Finally, the lipid panel is also commonly performed, as having diabetes is a risk factor for cardiovascular disease.
Routine blood work assesses numerous important parameters, including specific blood cell counts, electrolyte concentrations, and various indicators of liver and kidney function. It can detect common red flags, especially to identify nutritional deficiencies, diabetes, or potential signs of kidney, liver, cardiovascular disease, and more.
Talk to your healthcare provider about your specific results and trends over time to get the most thorough understanding and accurate and timely diagnosis and treatment for any conditions. Providing your thorough medical and family history and reporting any health symptoms or concerns can help your healthcare provider better understand which other laboratory tests would be most useful for your specific situation.
