Blood tests are useful tools for uncovering many diseases and disorders. They detect abnormally high or low levels of substances that may indicate a variety of conditions, including sources of pain ranging from Lyme disease to sickle cell anemia to types of arthritis.

Blood tests may be ordered for a number of reasons, including:

• Screening for a disease before symptoms appear
• Helping determine a diagnosis
• Monitoring the progression of a disease
• Monitoring the effectiveness of a patient’s treatment

Common blood tests include:

• Complete blood count (CBC). Measures the number of red blood cells, white blood cells and platelets.
  
  
• C-reactive protein test and sedimentation rate. Indicate inflammation.
  
  
• Enzyme test. Detects damage to tissues and assesses functioning of the body’s systems.
  
  
• Rheumatoid factor test. Measures an antibody that may indicate diseases such as rheumatoid arthritis.
  
  
• Waste product test. Helps detect gout and kidney damage due to conditions such as lupus.

Depending on the amount of blood required for the test, blood can be drawn from a vein puncture (venipuncture), artery puncture (arterial puncture) or skin puncture. Obtaining a blood sample takes only a few minutes, and most patients find blood tests to be virtually painless.

Some blood tests require fasting, but most involve little or no preparation, and patients can generally return to their usual daily activities afterward. Additional diagnostic tests such as urinalysis, imaging tests or biopsy may be necessary to confirm a diagnosis.

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

Blood tests serve a number of purposes related to the diagnosis and monitoring of various conditions and diseases. They may be used to:

• Determine a person’s risk of developing a disease
• Screen for a disease before signs and symptoms appear
• Help determine a diagnosis
• Rule out other diseases during diagnosis
• Monitor the progression of a disease
• Monitor the effectiveness of a patient’s treatment
• Detect complications of a condition
• Detect the spread of the disease to other areas of the body  
• Detect recurrence of a disease

Although blood tests may help detect many diseases, additional tests are usually necessary to verify the diagnosis.

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

• Vein puncture (venipuncture). A needle is inserted directly into a patient’s vein to draw blood into one or more tubes for laboratory analysis. 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 pricked with a needle to produce a drop of blood that is then collected for analysis.
  
  
• 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.

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 blood cells, white blood cells and platelets)

Certain blood tests are performed routinely to monitor people with chronic diseases, such as glycohemoglobin tests for people with diabetes. In addition, blood tests such as a cholesterol profile and glucose test are recommended for everyone periodically.

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 number and types 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 of the blood to form a 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 proper balance. Biochemicals and other substances that may be analyzed include:

• Sodium
• Cholesterol and other fats
• Vitamins and minerals
• Enzymes
• Hormones
• Blood gases
• Certain prescription drugs
• Illegal/recreational drugs
• Alcohol

Biochemical tests not only accurately measure these substances, but they can also be used to indicate how well some organs and systems are functioning. Measuring the amount of certain enzymes in the bloodstream can indirectly reflect the progression of a disease and its effect on the body.

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 is placed on a glass slide for examination under a microscope. Sometimes the blood smear 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 performed 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.

A variety of blood tests may be used to determine base levels of substances in blood or to screen for or identify certain conditions, many of which are characterized by inflammation. These include lupus and many forms of arthritis, such as rheumatoid arthritis and gout. These common blood tests include:

• Autoantibody testing such as an antinuclear antibody test (ANA test). Checks blood levels of antibodies that are often present in patients with certain autoimmune disorders such as lupus. According to the American College of Rheumatology, nearly everyone with lupus tests positive for antinuclear antibodies. However, other conditions (including rheumatoid arthritis, Sjogren’s syndrome, polymyositis and scleroderma) and the use of certain medications may also result in a positive ANA test. Further testing is necessary to establish a diagnosis.
  
  
• Basic metabolic panel (BMP). A group of tests that are often ordered in hospital emergency rooms because their components provide important information about a patient’s kidneys, electrolytes and acid/base balance, in addition to glucose (blood sugar) levels. Significant changes in these test results can indicate acute conditions, such as kidney failure, insulin shock or diabetic coma, respiratory distress or changes in heart rhythm.
  
  
• Blood differential. Also called a white blood cell (WBC) count. Measures the numbers of white blood cells in a blood sample. This test also includes information about abnormal cell structure and the presence of immature cells. A patient’s WBC count may increase as a result of infection or decrease with use of certain medications or in response to certain diseases, such as lupus. In addition, a low level of WBCs indicates that a patient may be at higher risk for infections.
  
  
• C-reactive protein test. A nonspecific test for detecting general inflammation. An elevated level of this protein produced by the liver suggests an inflammatory disease such as rheumatoid arthritis.
  
  
• Coagulation test. Measures how long it takes a person’s blood to clot (coagulate). This test is ordered for disorders that interfere with coagulation and to monitor patients taking anticoagulant drugs. Patients using anticoagulants may also be monitored with a test called INR (international normalized ratio).
   
• Complement. Measures the blood levels of a group of proteins (complement) that helps destroy foreign substances that enter the body. Patients with lupus often exhibit low blood levels of these proteins. This type of blood test is also useful in evaluating kidney damage and in monitoring the progression of a disease.  
  
  
• Complete blood count (CBC). Measures the number of red blood cells, white blood cells and platelets in a patient’s blood as well as the amount of hemoglobin (a substance that carries oxygen throughout the body) in the red blood cells and a number of other factors. Some rheumatic conditions or certain drugs used in the treatment of arthritis are associated with low counts of white blood cells (leukopenia), red blood cells (anemia) or platelets (thrombocytopenia). Patients who take medications that affect the CBC must have periodic blood testing for monitoring.
  
  
• Electrolyte panel. Measures various minerals, abnormal levels of which can suggest conditions ranging from cancer to kidney disease. 
  
  
• Enzyme test. A group of blood tests that measure enzyme (proteins required for chemical reactions to take place in cells) levels in the blood. These tests assess how well the body’s systems are functioning and whether any tissue damage has occurred. For example, cardiac enzyme tests are used in making the diagnosis of a heart attack and determining the extent to which the heart muscle was damaged.
  
  
• Genetic tests. Screen for genetic abnormalities that may indicate a risk of certain diseases, such as cancer.
  
  
• Glucose test. Measures the amount of sugar (glucose) in a patient’s blood sample. Glucose levels are measured mostly to diagnose diabetes and to monitor its control and treatment. In rare cases, greater-than-normal levels (hyperglycemia) may indicate acromegaly, a painful metabolic disorder that causes enlargement of a patient’s bones. Diabetic patients generally undergo a glycohemoglobin test every few months to assess long-term management of their condition.
  
  
• HLA–B27 antigen test. Checks for a genetic marker in white blood cells. Its presence may indicate many inflammatory conditions including ankylosing spondylitis and Reiter’s syndrome.
  
  
• Lipid profile (cholesterol test). A group of tests that measure total cholesterol, “good” HDL cholesterol, “bad” LDL cholesterol, “very bad” VLDL cholesterol and triglycerides. These tests are good indicators of a patient’s risk of heart attack or stroke.
  
  
• Liver function test. Used to assess the functioning of the liver and to diagnose various disease associated with liver.
  
  
• Lyme serology. A group of blood tests that confirm a diagnosis of Lyme disease. These tests detect a patient’s immune response to the infectious agent that causes the inflammatory disease.
  
  
• Rheumatoid factor test. Detects the presence of rheumatoid factor (RF), an antibody found in the blood of many patients with rheumatoid arthritis. RF may also be found in other autoimmune conditions such as Sjögren syndrome and sometimes in healthy people. Also, this test may be negative in some cases of rheumatoid arthritis when the disease is in remission, with no flare–ups of inflammation. Therefore, further testing may be necessary to confirm a diagnosis.
  
  
• Sedimentation rate (sed rate). Measures the rate at which red blood cells (erythrocytes) separate from the liquid part of blood (plasma) and fall to the bottom of a test tube, forming sediment. Higher sed rates indicate the presence of inflammation and are typical of many forms of arthritis (e.g., rheumatoid arthritis, ankylosing spondylitis) and many of the connective tissue diseases (e.g., lupus).
  
  
• Sickle cell test. Indicates the presence or absence of the abnormal hemoglobin (a substance in the red blood cells that carries oxygen throughout the body) that causes sickle cell anemia, a painful condition characterized by abnormalities in a patient’s red blood cells.
  
  
• Serum myoglobin. Determines damage to muscle, such as from a traumatic injury or heart attack, and predicts a recurrence of polymyositis.
  
  
• Thyroid test. Measures thyroid hormones to help diagnose thyroid diseases.
  
  
• Total serum protein. Measures the levels of protein to help diagnose conditions including kidney disease, liver disease, heart failure and high blood pressure.
  
  
• Tumor marker tests. Detect substances that may be produced by cancer cells, such as prostate specific antigen (PSA). Conditions including prostatitis can also elevate PSA. 
  
  
• Waste product test. A group of blood tests that measure the levels of specific waste products in a patient’s blood sample. They commonly test for uric acid, creatinine and blood urea nitrogen (BUN). When the kidneys are not working properly, waste products can build up in the body. The results of these tests can be used during the diagnosis of several diseases, including gout and lupus, as well as to monitor for underlying kidney disease.

Preparation for blood tests depends on the requirements of each specific test. Physicians will advise patients beforehand on the preparations required for each type of blood test.

In most cases, minimal preparation is necessary. The patient may just need to reduce or stop the use of certain medications and/or vitamins at some point prior to the test. Additionally, food intake and exercise may be temporarily restricted or suspended, such as an overnight fast for some glucose tests. Alcohol and caffeine should also 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. 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 physician or medical professional will also ask questions about the patient’s medical history prior to administering the test.

Having blood drawn for a blood test is an easy and nearly painless process for most people. If the test only requires a drop or two of blood, then just a prick of the finger, earlobe or heel (in the case of infants) can provide enough blood for testing.

A sterile, sharp lancet is used for pricking the patient’s skin. Then, the technician will gently squeeze the punctured area to extract drops of blood that are collected in tiny glass tubes. To stop the bleeding, sterile gauze is applied with light pressure to the punctured area. A bandage is usually not necessary since bleeding is minimal in most cases.

When a substantial amount of blood is required, it is usually drawn from a vein in a process called venipuncture. A needle is inserted into a vein, usually at the end of the elbow or on the back of the hand. The technician cleans the area around the puncture 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 then 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 scheduled. Usually, it is around 7 milliliters. The technician may change test tubes more than once 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:

• A lavender top indicates that the tube contains an anticoagulant, which prevents the collected blood sample from clotting.
  
  
• A red top indicates that the tube contains no anticoagulants, allowing serum and the blood to form a blood clot.
  
  
• A gray top indicates 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 whole process usually 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. If soreness is present, patients can immediately apply a warm compress to the puncture site and repeat the application every three hours until the discoloration or pain subsides.

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 the tests performed. Based on the test results, additional blood tests may be ordered.

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. When a person has arthritis or another disease or health problem, results may be higher or lower than normal – or “outside of the normal range.” When a physician sees that a blood test is outside of normal range, the tests may be repeated to verify results or additional tests may be ordered to determine the underlying causes behind the abnormality.

Normal ranges for some tests may vary slightly from lab to lab, especially between labs that use machines to perform blood tests and those in which blood tests are performed 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.

Although blood tests are very useful in the diagnosis of many conditions or diseases that cause chronic pain, other diagnostic tests are usually performed to determine the source of the pain and inflammation. These may include:

• Imaging tests. Tests that produce images of body parts, such as arthrography or other as x-rays, bone scan or other radionuclide imaging, CAT scan, MRI or ultrasound.

• Synovial fluid analysis. Test that analyzes fluid from an inflamed joint that is useful in diagnosing septic arthritis or juvenile rheumatoid arthritis.
  
  
• Electrodiagnostics. Tests that measure the electrical activity of nerves and muscles, such as electromyography or nerve conduction studies.
  
  
• Biopsy. Procedure in which a small sample of tissue is collected and examined under a microscope.
  
  
• Spinal tap (lumbar puncture). Insertion of a needle into the spinal canal to collect cerebrospinal fluid, to diagnose conditions including meningitis, encephalitis and some headaches. 

In addition to the blood tests, a urine test may also be used to diagnose certain inflammatory diseases, such as gout, one of the most painful forms of arthritis.

There are very few risks or side effects associated with blood tests. Sometimes, bruising may occur at the site of injection. This can be minimized and alleviated by keeping direct pressure on the spot for several minutes after the syringe has been removed.

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

People with bleeding disorders or who are taking anticoagulants, including aspirin, may have problems with continued bleeding. Those who experience these side effects should consult their physician.

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 regarding blood tests:

1. Why is a blood test being recommended for me?
2. Which type or types of blood testing will I have?
3. What can this testing tell about my condition?
4. How should I prepare for the test?
5. Are there any risks associated with my test?
6. How long will I have to wait for results?
7. What do my test results show?
8. Will I need additional tests to confirm diagnosis?
   
   
9. Do I need regular blood testing to monitor my condition or medication?
   
   
10. If my blood work shows I need treatment, what are my options?
    
    
11. Should I have regular screening for cholesterol, diabetes or other conditions?