Endocrine Blood Tests

Endocrine Blood Tests


Blood tests are useful tools for uncovering disorders in the human body. For many patients with diabetes, blood testing is a part of daily life. For others, routine blood tests may be ordered by a physician only once or twice a year.

Blood tests are used to diagnose diabetes as well as prediabetes, thyroid conditions and other endocrine disorders. In people with diabetes, blood tests are used to measure glucose (blood sugar) levels, to monitor the effectiveness of treatment, and to detect, prevent and delay the onset of diabetic complications.

Though traditionally performed in physician offices and laboratories, certain over-the-counter blood tests can be performed in the home.

Depending on the amount of blood required for the test, blood can be drawn from a vein (venipuncture), skin puncture or artery (arterial puncture). For diabetic individuals, blood is usually drawn from a vein or fingertip. Newer home tests allow for alternative site testing from the upper arm, forearm, hand, calf, abdomen or thigh.

Obtaining blood samples takes only about five minutes, and most patients find them to be virtually painless. For most blood tests, there is very little preparation, and people can generally return to their usual daily activities after testing.

About blood tests

A blood test uses a sample of blood to detect and measure various factors in the blood. It is important to measure these factors because abnormally high or low levels may affect normal body function.

Blood tests serve a number of purposes related to the diagnosis and management of diabetes and other endocrine disorders. These purposes include:

  • To screen for prediabetes (glucose intolerance) and diabetes in high-risk people
  • To help diagnose diabetic conditions when suspected, including prediabetes, type 1 diabetes, type 2 diabetes, gestational diabetes and other forms of diabetes
  • To provide glucose (blood sugar) readings for diabetes management
  • To monitor the effectiveness of a patient’s diabetes treatment
  • To detect consequences of poorly controlled diabetes, such as hyperglycemia, hypoglycemia or diabetic ketoacidosis
  • To prevent or delay the onset of diabetic complications (e.g., retinopathy, nephropathy, neuropathy, heart conditions) by alerting patients to problems that can be treated
  • To help detect and monitor hyperthyroidism, hypothyroidism and other endocrine conditions

Samples of blood may be taken in one of three ways:

  • Vein puncture (venipuncture). A needle is inserted directly into a vein to draw blood into one or more tubes. Blood is usually drawn from a vein in the inner arm, opposite the elbow.
  • Skin puncture. Used when only a small amount of blood is needed to perform the desired blood test. The skin of the finger, earlobe or heel (in infants) is jabbed with a needle to produce a drop of blood that is then collected for testing.
  • Artery puncture (arterial puncture). Used only when the blood test needs to be performed on a sample of oxygen-rich blood traveling from the heart to the body via the arteries. Blood is usually drawn from an artery in the side of a wrist.

Most blood samples are collected from a vein or by skin puncture. Diabetic individuals performing home blood tests will usually collect a sample by pricking their finger with a lancet. Some newer glucose meters allow foralternate site testing from the upper arm, forearm, hand, calf, abdomen or thigh.

Blood tests can be performed on different parts of the blood, including:

  • Whole blood (blood that has not been separated into its many components)
  • Blood plasma (the liquid part of the blood)
  • Blood serum (plasma that has had the clotting agent removed)
  • Blood cells (the individual red, white and platelet cells)

Certain tests are routinely run on the blood of people with diabetes. Some blood tests, such as cholesterol tests, are recommended at least once a year. Other tests, such as glucose self-measurement, may have to be performed several times a day. Home blood tests are available to make blood testing more convenient (see Home blood tests).

Types and differences of blood tests

Hundreds of blood tests are performed every day in laboratories and in people’s homes. In general, there are four main types of blood tests:

  • Hematology tests
  • Biochemistry tests
  • Microbiology tests
  • Serology tests

Hematology tests examine the blood to identify:

  • The types and numbers of blood cells that are present (e.g., red blood cells, white blood cells and platelets)
  • The appearance of the cells, especially their maturity
  • The ability for the blood to form a blood clot and the speed at which clotting occurs

Biochemistry tests measure the levels of normally occurring chemicals and biochemicals in the blood, both individually and in relation to other chemicals. These measurements are compared to normal ranges and are used to determine whether blood biochemicals are in a proper and healthy balance. Biochemicals and other substances that may be studied include:

  • Cholesterol and other fats
  • Vitamins and minerals (e.g., sodium, calcium, potassium)
  • Hormones
  • Blood gases
  • Prescription drugs
  • Illegal drugs
  • Alcohol

Not only can biochemical tests precisely measure these substances, but they can also be used to indicate how well some organs and organ systems are functioning. For instance, the amount of glucose in the bloodstream can help diagnose or monitor diabetes, and levels of thyroid hormones in the blood can indicate hypothyroidism or hyperthyroidism.

Microbiology tests examine blood for the presence of infectious microscopic organisms such as:

  • Bacteria
  • Fungi
  • Viruses (in most clinical labs a serology test is used)
  • Parasites

Microbiology tests include:

  • Smears, in which a small amount of blood or other bodily fluid is placed on a glass slide for examination under a microscope. Sometimes the blood smear or fluid is stained with special dyes before examination.
  • Blood cultures, in which a small amount of blood is placed in a nutrient broth, incubated for days or weeks and then examined for growth of disease-causing bacteria.

Serology tests (tests done on blood serum) can detect the presence of antibodies that are produced by white blood cells to attack microscopic organisms. They are frequently used to detect viral diseases. Most hospital laboratories do not have the equipment or specially trained personnel necessary to isolate the viruses themselves, so serology tests are done instead to identify the infecting organism by studying the antibodies produced against it.

Common blood tests with diabetes

The most common blood tests used in the diagnosis and management of diabetes and related complications include:

  • Autoantibody tests. Detect self-antibodies in a person’s blood. The presence of certain autoantibodies in the body can indicate an autoimmune disorder such as type 1 diabetes, Hashimoto’s thyroiditis, rheumatoid arthritis or lupus.
  • C-peptide test. Measures levels of the protein fragment C-peptide to determine the amount of insulin a person’s body is making. The pancreas releases C-peptide and insulin into the blood in equal amounts. This test may be ordered to distinguish type 2 diabetes from type 1, evaluate hypoglycemia or hyperinsulinemia, or determine the effectiveness of a pancreas transplant or an islet cell transplant.
  • Cholesterol test. Also known as a blood fat profile or lipid profile, this test measures fats and fat-like substances in the blood that, if abnormally high, have been associated with heart disease. Diabetic patients are at higher risk for high cholesterol, atherosclerosis and related heart problems. A cholesterol test includes levels for:

    • Total cholesterol
    • LDL (low-density lipoprotein) “bad” cholesterol
    • HDL (high-density lipoprotein) “good” cholesterol
    • Triglycerides
    • VLDL (very-low-density lipoprotein) “very bad” cholesterol

  • Complete blood count (CBC). Routine test that measures levels of red blood cells, white blood cells and platelets. Abnormal results can be due to many conditions ranging from infections to heart attack and will prompt further testing.
  • Glucose tests. Measure the amount of glucose (blood sugar) in a person’s blood. Abnormally high levels of glucose may indicate that the person has prediabetes (glucose intolerance) or diabetes. In a person already diagnosed with diabetes, they can reveal the quality of glucose control. There are several tests used to measure glucose, including:

    • Fasting plasma glucose test (FPG). Measures the amount of glucose in a person’s blood after not eating for 12 to 14 hours.
    • Glucose challenge test (GCT). Measures the amount of glucose in a person’s blood one hour after the patient drinks a solution containing 50 grams of glucose.
    • Oral glucose tolerance test (OGTT). A patient’s blood sample is taken after an overnight fast. The patient then drinks a high-glucose beverage. Additional blood samples are then taken at two- to three-hour intervals to measure how the body uses glucose over time.
    • Random plasma glucose test. Measures the amount of glucose in a person’s blood at any given time without fasting or other preparation.
    • Two-hour postprandial (after meal) blood sugar test. Measures the amount of glucose in a person’s blood two hours after eating.
    • Glycohemoglobin test (A1C test). Used to assess diabetes management, this test indicates a person’s average blood glucose level over the past two to three months. The test measures the amount of glucose that is attached to the hemoglobin in a person’s blood. That quantity is proportional to the amount of glucose in the blood.
    • Fructosamine test. Used to assess diabetes management, this test provides a person’s average glucose level for the past three weeks. The test measures the amount of glucose that has attached itself to the protein molecules in a person’s blood. That quantity is proportional to the amount of glucose in the blood.

      Though glycohemoglobin and fructosamine tests do not directly test glucose levels, they are often thought of as glucose tests because they do indicate glycemic control.

  • Ketone tests. Measures the amount of ketones in a person’s blood. The presence of an abnormally large amount of ketones (ketosis) is a sign that the body is burning fat for energy instead of glucose because it does not have enough insulin available. It may indicate an increased risk of a potentially life-threatening condition called diabetic ketoacidosis.
  • Waste product tests. This group of blood tests measures the levels of waste products in the blood, including blood urea nitrogen (BUN), creatinine and uric acid. Abnormally high amounts of waste products in the blood can be a sign of kidney disease, such as diabetic nephropathy.

Additional blood tests that may be used for diabetes, other endocrine disorders or complications include:

  • C reactive protein (CRP) test or erythrocyte sedimentation rate (ESR). Nonspecific tests that indicate inflammation somewhere in the body.
  • Coagulation tests. Measure the amount of time it takes for an individual’s blood to clot under standardized conditions. Patients taking anticoagulant medication may be monitored with a blood test called INR (international normalized ratio).

    • Electrolyte panel. Measure electrolyte levels to assess the general functioning of a patient’s organ systems. Electrolytes that are often measured include calcium, potassium, chloride and sodium. An electrolyte panel may be ordered for patients being treated for diabetic ketoacidosis.
    • Enzyme test. Measures levels of certain enzymes to help indicate conditions ranging from pancreatitis to heart attack to cancer.

  • Genetic testing. Examines chromosomes and/or genes for abnormalities to determine whether a person has a disease or is at risk for developing a disease. The test is also used to determine the likelihood that a relative will develop certain diseases, such as maturity-onset diabetes of the young (MODY), a rare, genetic form of diabetes. Children of parents with MODY are most often diagnosed through genetic testing even before symptoms occur.

    A positive genetic blood test result indicates the genetic mutation has been inherited from a family member with diabetes. With a positive result, yearly blood glucose evaluations are highly recommended.

  • Rheumatoid factor test. Helps diagnose rheumatoid arthritis, lupus and other inflammatory and autoimmune diseases. People with an autoimmune disease, such as type 1 diabetes or Hashimoto’s thyroiditis, are at increased risk for other autoimmune disorders.
  • Testosterone test. Can reveal low levels of testosterone (hypogonadism), a common cause of sexual dysfunction in diabetic men.
  • Total serum protein. Reveals abnormal levels of proteins, which may be due to kidney disease, heart failure, liver disease, high blood pressure or other disorders.
  • Tumor marker tests. Detect substances, such as prostate-specific antigen (PSA), that may indicate cancer when present in large amounts. Diabetes increases the risk of some cancers.
  • Thyroid blood tests. Routinely performed on newborns and often offered when adults have bloodwork. They help detect and monitor conditions including Graves’ disease and other forms of hyperthyroidism, hypothyroidism and thyroiditis.

Before and during the blood test

Preparation for blood tests varies according to the requirements of each specific test. In most cases minimal preparation is necessary. The patient may need to reduce or stop certain medications and vitamins at some point prior to the test. Additionally, food intake and exercise may be temporarily restricted or suspended. Alcohol and caffeine should be avoided prior to a blood test.

On the day of the test, the procedure will be explained and patients will have the opportunity to ask questions. The medical professional will also ask questions about the patient’s medical history before the test, to determine if the patient is taking any medications that will interfere with the test’s accuracy or has any history of clotting problems.

A person performing a blood test at home should be aware of factors that can interfere with the test’s accuracy. This information is usually provided by the test’s manufacturer.

Drawing blood for a blood test is an easy and virtually painless process for most people. If the test requires only a drop or two of blood, then a simple prick of the finger, earlobe or heel (in the case of a baby) can provide enough blood for testing. Some glucose meters allow for alternate site testing from the upper arm, forearm, hand, calf, abdomen or thigh.

A sterile, sharp lancet is used to prick the skin. The technician will then gently squeeze the puncture area to produce drops of blood that are collected in tiny glass tubes. With home blood testing, the patient squeezes out the necessary amount of blood and applies it to the test kit or meter. Light pressure and sterile gauze are then applied to the puncture site to stop the bleeding. A bandage is usually not necessary.

If a substantial amount of blood is needed, it is usually drawn from a vein in a process called venipuncture. Venipuncture is not used with home blood testing.

During venipuncture, a needle is inserted into a vein – usually at the end of the elbow or on the back of the hand. The area around the puncture site is cleaned with rubbing alcohol and a wide elastic band or piece of latex tubing may be placed around the upper arm to slightly increase pressure in the vein. One end of a sterile double-ended needle that has been attached to an open-ended syringe (which contains an empty test tube) is inserted into the vein. Because the test tube contains a partial vacuum, blood flows directly from the vein through the double-ended needle and into the test tube.

The precise amount of blood to be drawn is determined by the type and number of tests to be done. It is usually around 7 milliliters. The technician may change test tubes once or twice during a venipuncture to either allow for more blood to be collected or to change the type of tubing being used. Tubes are marked with different-color tops that indicate the way in which the collected blood will be preserved:

  • Lavender tops indicate that the tube contains an anticoagulant, which prevents the collected blood from clotting.
  • Red tops indicate that the tube contains no anticoagulants, allowing the blood to form a blood clot.
  • Gray tops indicate that the tube contains a preservative, which keeps glucose from breaking down in the tube.

After the necessary amount of blood is drawn, the needle is withdrawn and a small cotton ball or pad is applied with light pressure over the puncture site. After several minutes, the cotton will be discarded or replaced, and a small bandage will be placed on the puncture wound. The entire process takes less than 10 minutes.

Despite the precautions taken to avoid bruising and soreness, it does sometimes occur. Typically, this is not a cause for great concern. To minimize soreness, patients may immediately apply a warm compress to the puncture site and repeat the application every three hours until the discoloration or pain subsides.

If blood must be taken from an artery instead of a vein, it is usually drawn from a very small artery located on the inside or the top side of the wrist.

After the blood test

Following the withdrawal of blood in a physician’s office or laboratory, patients may resume medications and food intake according to their physician’s orders. Immediately after the blood sample is taken, the test tubes are labeled with the date and the patient’s name, and they are sent to the laboratory for testing. Results are usually returned within 24 hours, depending on which tests need to be performed. Based on the test results, additional blood tests may be ordered.

Most home blood tests provide results in less than a minute. Others may require the patient to mail the test kit back to the company for analysis. The company would then send results back to the patient.

Test results are always evaluated in relation to the “normal range” for that test. The range of values considered to be normal is the range of test results from the blood of normal, active, healthy people. For people with diabetes or another endocrine disease or health problem, blood test results may be higher or lower than normal, or “outside of the normal range.” A physician who sees that a blood test is outside of normal range may order repeat tests to verify results or additional tests to determine the underlying causes behind the abnormality.

Patients performing home blood tests should always discuss abnormal readings with their physician. Diabetic individuals who perform glucose (blood sugar) tests should keep a record of their test results and show the results to their physician during appointments.

Normal ranges for some tests may vary slightly from lab to lab, especially in labs that use machines to perform blood tests and those that perform blood tests by hand. Frequently, results of a patient’s blood test are compared to another “known” blood sample taken from a healthy individual that is run at the same time and is designated as the “normal control.” When the “normal control” sample falls within the normal range, or reaches a specific “known” measurement, the laboratory results confirm that the blood test has been carried out accurately.

Potential risks with a blood test

There are very few risks or side effects reported with blood tests. Occasionally, bruising is reported at the injection site. This can be minimized by keeping direct pressure on the spot for several minutes after the needle has been removed.

In rare situations, the vein used to obtain the sample may become inflamed. Applying warm compresses to the spot several times daily can help reduce the swelling.

Patients with bleeding disorders or who are taking anticoagulants (including aspirin) may have problems with continued bleeding. Patients who experience these side effects should consult with their physician.

Home blood tests

Blood testing has traditionally been performed at physician offices and laboratories. However, many home blood tests are available over the counter. These tests allow for convenient blood testing from anywhere.

The most popular way for people with diabetes to perform home glucose blood tests is with a glucose meter. Testing glucose levels with a typical meter requires a person to place a small sample of blood on a test strip. Test strips are coated in chemicals that combine with glucose. When the sample is read by the monitor, it measures how much glucose is present.

Some glucose meters also test for other substances in the blood, including ketones, glycohemoglobin (A1C) and cholesterol. Separate testing kits are available to measure these substances as well.

Although not as accurate as glucose meters, visually read glucose strips are also available. These strips require a drop of blood to be placed on a chemically coated test strip. The chemicals on the strip’s test pad react with the glucose in the blood and it changes color accordingly. The user then compares the color on the test pad to a color chart on the side of the vial and estimates their glucose level.

Though home blood testing is a convenient way for diabetic patients to monitor their health, there are drawbacks. One major disadvantage is that there is a greater risk for inaccuracy than with professionally administered tests. Meter malfunction and human error can lead to inaccurate test results.

Because reading a color chart is sometimes necessary to interpret test results, a person with colorblindness would be unable to use some tests.

Patients are advised to consult their physician about where to draw blood when testing at home. Two recent studies suggest that forearm readings generally appear comparable with fingerstick results but may overestimate glucose levels during periods of hypoglycemia (low glucose).

Not all home blood tests provide results to the patient. Some tests require a blood sample be applied to the test kit and mailed back to the company. The results are then returned to the patient for evaluation.

Questions for your doctor about blood tests

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about blood tests:

  1. Why do I need a blood test?
  2. Which type or types of blood testing do you recommend for me?
  3. Do I need to fast, withhold medication or do anything else to prepare for the test?
  4. When and where will my testing take place?
  5. What is the normal range for me according to this lab’s testing methods?
  6. Who will explain my test results to me, and when?
  7. What do my test results show? Could any factors be affecting my test results?
  8. Do I need any follow-up blood tests, urine tests, imaging studies or other tests?
  9. If my test shows I need to start or change treatment, what are my options, and which do you recommend?
  10. How often should I have laboratory blood tests?
  11. Should my relatives and I have genetic blood testing if diabetes runs in our family?
  12. How often should I perform glucose monitoring or other types of blood tests at home?
  13. When I do a home blood test, what site should I draw blood from?
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