Interpreting Lab Results
When viewing your lab results, it is important to understand and be able to interpret what they mean. Every test that your physician orders provides information to help them diagnose and assess your health. Some of the most common lab tests used during a routine physical exam are listed below. Click on each name to read specific information about these tests.
Complete Blood Count (CBC)
Comprehensive Chemistry Panel
Hemoglobin A1c (HbA1c)
Thyroid Stimulating Hormone (TSH)
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Complete Blood Count (CBC)
A Complete Blood Count (CBC) gives important information about the kinds and numbers of cells in your blood. The blood specimen is run through an instrument that uses a laser to count and categorize the various cells that make up your blood.
- Red Blood Cells (RBC) are the most common types of blood cells, and the body's principal means of delivering oxygen from the lungs to all body tissues via the blood. This oxygen delivery happens through a complex molecule called hemoglobin. The average number of red blood cells in women is four to five million per cubic millimeter, and five to six million per cubic millimeter in men. Red blood cells contain approximately 65% of the body's iron; therefore, a doctor may use your count to determine if anemia is present.
- White Blood Cells (WBC) are cells that make up your immune system and defend the body against infection and foreign materials. Your bone marrow produces several types of white blood cells, all of which are found throughout your body, blood, and lymph nodes. The number of white blood cells is often an indicator of disease. There are normally 4,000 to 11,000 white cells in a liter of blood. If your white blood cell count rises, it could mean an infection has begun and your doctor may require additional tests.
- Hemoglobin (HGB) is a protein carried by red blood cells. The protein picks up oxygen in the lungs and delivers it to organs and tissues of the body to keep all cells alive. In women, a normal hemoglobin level is considered to be 12 to 15 grams. Men range from 13 to 16.5 grams, and children from 11 to 16 grams. Hemoglobin is also used to assess the presence of anemia.
- Platelets are cells that circulate through the blood and are involved with the formation of blood clots. Platelets help form a web around a wound when it is bleeding. If you have low levels of platelets, you could be predisposed to bleeding. If you have a platelet level that is too high, you could develop abnormal clots called thrombosis. Platelets circulate in your blood for about one week and then they are destroyed by the liver and the spleen as new ones are produced by your bone marrow. Normal platelet levels are anywhere from 150,000 to 400,000 per microliter of blood.
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A Lipid panel is performed by collecting a blood specimen that is allowed to form a clot. The clot is then placed in a centrifuge to produce a serum that is tested for total cholesterol, triglycerides, HDL, and LDL.
- Cholesterol is a fat found in all cell membranes that is transported throughout your blood. Most of the cholesterol that is found in your blood is either produced by your body or is introduced by your diet. Cholesterol is very important in regards to the body's biochemical processes, such as cell membrane production and the metabolism of fat-soluble vitamins including A, D, E, and K. Cholesterol is also important in the production of estrogen and testosterone hormones. Since cholesterol is insoluble in the blood, it is carried by lipoproteins. The two most important lipoproteins are HDL and LDL. High levels of LDL and low levels of HDL are associated with heart disease because they promote plaque build-up in the coronary arteries of the heart.
- LDL (bad cholesterol) is responsible for carrying cholesterol to body tissues where it is deposited and can then clog the arteries of the heart.
- HDL (good cholesterol) scrubs the artery walls, picks up the cholesterol-like material, and carries it back to the liver to be excreted out of the body.
- Your total cholesterol number is made up of the LDL and HDL, and should be under 200 mg/dL. Your LDL should be less than 100 mg/dL and your HDL should be greater than 60 mg/dL. You can have a normal total cholesterol with a low HDL and a high LDL, which is associated with atherosclerosis.
- Triglycerides are formed from a glycerol molecule, and make up most of the fats digested by humans. It is the main component of vegetable oil and animal fats. Triglycerides play an important role in the metabolism process as an energy source and the transporter of dietary fats. They contain more than twice as much energy as carbohydrates and proteins. In the body, high levels of triglycerides in the blood have been linked to artherosclerosis (plaque in the coronary arteries), and by extension, the risk of heart disease and stroke. High triglycerides have also been associated with pancreatitis. Triglyceride levels often remain temporarily high for a period of time after eating, so it is important to obtain blood tests after an 8 to 12 hour fast. Normal levels of triglycerides in the blood are less than 150 mg/dL for both males and females. Moderate consumption of fats, alcohol, and carbohydrates, as well as moderate exercise are essential to reducing triglyceride levels in the blood.
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Comprehensive Chemistry Panel
- Blood Sugar (Glucose) Blood sugar concentrations, or glucose levels, are tightly regulated in the human body. Normally the blood glucose level is maintained between 90 and 120 mg/dL. Glucose levels rise after meals for an hour or two, and are usually lowest in the morning before the first meal of the day. Failure to maintain blood glucose in the normal range lead to conditions of persistently high (hyperglycemia) or low (hypoglycemia) blood sugar. Diabetes mellitus is characterized by persistent hyperglycemia. Hypoglycemia or low blood sugar occurs when the blood sugar drops too low. Symptoms may include lethargy, impaired mental function, and irritability. If blood sugar levels remain too high for a long period of time, damage can occur in the eyes, nerves, and kidneys.
- Blood Urea Nitrogen (BUN) is a test that measures the amount of nitrogen in the blood in the form of urea, and a measurement of renal function. Urea is a substance secreted by the liver, and removed from the blood by the kidneys. The most common cause of an elevated BUN is poor kidney function. An abnormally high BUN can indicate impaired kidney excretion of urea. This may be due to temporary dehydration, shock, or acute kidney disease. A low BUN usually is of little significance, but causes may include malnutrition (not enough protein) or excessive alcohol consumption. Over hydration or pregnancy can also cause a BUN to be low.
- Electrolytes ( Sodium, Potassium, Chloride and Carbon Dioxide) are substances that become ions in solution and acquire the capacity to conduct electricity. Electrolytes are essential for the normal function of our cells and our organs.
- Sodium is the major positive ion in the fluid outside of cells. Sodium regulates the total amount of water in the body and transmission of sodium into and out of individual cells also plays a role in critical body functions. Many processes in the body, especially those involving the brain, muscles, and nervous system, require electrical signals for communication. The movement of sodium is critical in generation of these electrical signals. Too much or too little sodium can cause cells to malfunction.
- Potassium is the major positive ion found inside the cells. Among the many functions of potassium in the body are the regulation of heartbeat and function of the muscles. A serious increase or decrease in potassium can profoundly affect the nervous system and increase the potential for irregular heartbeats.
- Chloride is the major negative ion in the fluid outside of the cells and in the blood. Chloride plays a role in helping the body maintain a normal balance of fluids. Increased amounts of chloride can be found in diarrhea, certain kidney diseases, and sometimes in overactivity of the parathyroid glands. Chloride is normally lost in the urine, sweat, and stomach secretions. Excessive loss can occur from heavy sweating, vomiting, and adrenal gland and kidney disease.
- Carbon Dioxide (CO2) bicarbonate is an ion that acts as a buffer to help maintain the normal levels of acidity or pH of the blood and other body fluids. The acidity is affected by foods or medications that we ingest and the function of the kidneys and lungs.
- Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a constant rate by the body. The kidney mainly filters creatinine, and a serum creatinine test is simple and an excellent indicator of kidney function. If the filtering of the kidneys is deficient, blood levels of creatinine will rise. As part of creatinine testing, a secondary test called GFR (glomerular filtration rate) may be performed. The GFR is clinically important because it measures how well the kidneys are filtering. Creatinine levels can be higher in men because they have greater muscle mass. Certain medications such as ACE-inhibitors or Beta-blockers used for chronic heart failure can cause creatinine levels to be increased without having kidney problems.
- Calcium is essential in a healthy diet. It is needed for the normal growth and maintenance of bones and teeth, and calcium requirements must be met throughout life. Long-term calcium deficiency can lead to rickets and poor blood clotting, and in the case of a menopausal woman, it can lead to osteoporosis, in which the bone deteriorates and causes an increased risk of fractures. Lifelong deficits in calcium can affect bone and tooth formation. Calcium levels that are too high (hypercalcemia) can cause impaired kidney function and decrease the absorption of other minerals.
- Bilirubin is a brownish-yellow substance found in bile. It is produced when the liver breaks down old red blood cells. Bilirubin is then removed from the body through the stool and gives stool its normal brown color. Bilirubin is in the blood in two forms: Indirect bilirubin does not dissolve in water. It travels in the blood to the liver, where it is changed into a soluble form of direct bilirubin. Direct bilirubin dissolves in water and is made in the liver from indirect bilirubin. When bilirubin is high, the skin and whites of the eyes may appear yellow (jaundice). Jaundice may be caused by liver disease, blood disorders, or blockage of the bile ducts not allowing bile to pass from the liver to the small intestines. The bilirubin test checks liver function and bile duct blockages as well as conditions where the red blood cells are destroyed too quickly.
- Alkaline Phosphatase (ALP) is an enzyme in the blood, made mostly in the liver. Some conditions cause large amounts of ALP in the blood. These conditions include rapid bone growth (during puberty), bone disease (osteomalacia or Paget's disease), a disease that affects calcium levels in the blood (hyperparathyroidism), or damaged liver cells. The test for alkaline phosphatase is often done at the same time as other routine blood tests and checks for liver disease or bone problems.
- Total Protein serum testing measures the total amount of protein in the blood. It measures the amounts of two major proteins in the blood: albumin and globulin. Albumin is made mainly in the liver. It helps keep the blood from leaking out of the blood vessels. Albumin also helps carry medicines and other substances through the blood and is important for healing.
- Globulin is made up of different proteins called alpha, beta, and gamma types. Some globulins are made in the liver, while others are made by our immune system. Certain globulins bind with hemoglobin. Other globulins transport metals such as iron and help fight infections. Serum globulins can be separated into subgroups by a test called serum protein electrophoresis.
- Albumin is tested to check on liver and kidney function and to find out if your diet has enough protein. It can help determine the cause of ankle swelling or fluid collecting in the lungs or abdomen.
- Globulin can be tested to determine your chances of developing infections and is used to determine rare blood diseases such as multiple myeloma. The amounts of albumin and globulin are compared. Normally, there is more albumin than globulin and the ratio is greater than one.
- Aspartate Aminotransferase (AST) is an enzyme found in the blood. It is normally found in the red blood cells, liver, heart, muscle, pancreas, and kidneys. Low levels of AST are normally found in the blood. When body tissue or an organ such as the heart or liver is diseased or damaged, additional AST is released into the bloodstream. The amount of AST in the blood is directly related to the extent of the tissue damage. After severe damage, AST levels rise in 6-10 hours and remain high for about 4 days. Often AST is done at the same time as ALT. The ratio of AST to ALT sometimes can help determine whether the liver or other organs have been damaged. Certain medications can interfere with your AST test results. Please ask your doctor if you should be off of any medication prior to testing. Some herbs such as Echinacea and valerian can cause AST results to be abnormal.
- Alanine Aminotransferase ( ALT) is an enzyme found in the blood. It is mainly found in the liver, but also in smaller amounts in the kidneys, heart, muscles, and pancreas. ALT is measured to see if the liver is damaged or diseased. Low levels of ALT are normal in the blood, but when the liver is damaged or diseased, it releases ALT into the bloodstream, which makes the ALT levels go up. Most increases in ALT are caused by liver damage. If you are taking cholesterol-lowering medicine, your doctor will likely use ALT to make sure your medication is not damaging your liver.
- Certain medications can interfere with your ALT test results, so please ask your doctor if you should be off of any medication prior to testing. Some herbs such as Echinacea and valerian can cause ALT results to be abnormal.
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Hemoglobin A1c (glycosylated hemoglobin)(A1c)(HbA1c)
Hemoglobin A1c is a form of hemoglobin used primarily to identify the average blood glucose over a 3 month period. In the normal 120-day life span of a red blood cell, glucose molecules join hemoglobin inside the red cell, forming glycated hemoglobin. In individuals with poorly controlled diabetes, increases in the quantities of these glycated hemoglobins are noted.
Once a hemoglobin molecule is glycated, it remains that way. A buildup of glycated hemoglobin within the red cell reflects the average level of glucose to which the cell has been exposed during its life cycle. Measuring glycated hemoglobin assesses the effectivness of therapy by monitoring long-term serum glucose regulation. The HbA1c level is proportional to average blood sugar concentration over the previous four weeks to 3 months.
High levels of hemoglobin A1c are found in patients with diabetes mellitus. Hemoglobin A1c is recommended for checking blood sugar in people who are or might be pre-diabetic. It is also used to monitor blood sugar control in patients with diabetes every 3-6 months.
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Urinalysis is an array of tests performed on urine, and is one of the most commonly ordered tests when diagnosing illness, especially bladder infections. A part of the urinalysis can be performed by using a chemical dipstick that turns colors when dipped into fresh urine. The color change is interpreted as positive or negative by the laboratory staff. The typical components of urine tests include:
- Specific gravity reflects the degree of concentration or dilution of the specimen. Under appropriate conditions of fluid restriction or increased fluid intake, specific gravity measures the concentrating and diluting abilities of the kidney. Specific gravity is the highest first thing in the morning where a specimen is considered normal when it is between 1.003 and 1.030. Low specific gravity can occur in diabetics and patients with kidney disease. High specific gravity is seen in congestive heart failure, liver disease, excessive sweating, diarrhea, or vomiting.
- pH is a measure of the hydrogen ion concentration of the urine. A pH below 7 indicates an acidic urine sample. A pH above 7 indicates an alkaline urine sample. Normal kidneys are capable of producing urine than can vary from a pH of 4.5 to 8.0. Freshly voided urine from patients who are not on special diets is usually acidic, and has a pH of about 6.0. High protein diets produce acidic urine and certain medications can affect the pH .
- Glucose is the sugar most commonly found in urine. The presence of glucose in the urine occurs when the blood glucose level exceeds the capacity of the kidneys to reabsorb, causing the excess sugar to spill out into the urine. Glucose in the urine could be caused by diabetes or a kidney problem. A normal result for glucose is negative or none present.
- Ketones appear when there is an inadequate amount of carbohydrates in the diet. The body begins to metabolize and increases the amounts of fatty acids in the body and the by-product raises fat metabolism that appears in the blood and is excreted in the urine. Diabetes is known for making large amounts of ketones appear in the urine. A normal ketone result is negative or none present.
- Proteins in the urine are one of the most important indicators of kidney disease. One-third of the normal urine protein is albumin. A normal urine sample has 40 to 100 mg of protein. Protein in the urine, at high amounts, will require follow-up care by your physician. A normal protein result is negative or none present.
- Blood presence in the urine is an indication of damage to the kidney or urinary tract. Red blood cells, or free hemoglobin, in the urine is called hematuria and indicates bleeding in the urinary tract. This could be caused by infection or trauma and further testing is required. A normal urine blood test is negative or none present.
- Bilirubin in the urine is an early sign of liver disease. Bilirubin will appear in the urine when the amount in blood is increased. The presence of bilirubin requires further testing by your physician. A normal bilirubin is negative or none present.
- Nitrite tests look at the by-products produced by various bacteria. If there is a significant number of bacteria in the urine, the nitrite test can be positive. This means an infection is occurring and a urine culture is typically ordered. This test is important when a physician is trying to determine if you have a bladder infection.
- Leukocyte Esterase testing detects the esterase released from white blood cells in the urine. Usually the presence of a significant number of white blood cells in the urine indicates a urinary tract infection. Your physician may follow up with a urine culture.
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Thyroid Stimulating Hormone (TSH)
TSH is the test of choice when evaluating thyroid gland function. TSH is used to diagnose hyper (over active), or hypo (under active), thyroid activity. Patients are screened for TSH if they are showing symptoms of thyroid gland dysfunction. Physicians will also screen newborns for an under active thyroid, as well as use it to monitor thyroid replacement medication, diagnose and monitor female infertility, and help evaluate the functioning of the pituitary gland.
- A high TSH result often indicates an under active thyroid gland that is not responding to the stimulation of TSH due to some type of thyroid dysfunction. It can also mean that patients on thyroid medication are not receiving a high enough dose. Rarely, a high TSH can point to a problem with the pituitary gland such as a tumor.
- A low TSH result can indicate an over active thyroid gland or too much thyroid medication. An abnormal TSH, high or low, is usually followed by additional thyroid testing to determine the cause of the increase or decrease.