Blood tests detect abnormally high or low levels of substances in the blood that may indicate a variety of conditions, including digestive disorders or diseases. Traditionally performed in physician’s offices, laboratories and hospitals, they are useful tools for uncovering disorders in the human body.

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

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

Many digestive conditions involve blood tests in their diagnosis and treatment, in addition to other tests. One common blood test is a complete blood count (CBC), which measures the number of red blood cells, white blood cells and platelets in the blood. Other blood tests indicate the presence of certain antibodies, such as an antibody to the Helicobacter pylori bacteria, which can cause peptic ulcers.

Most blood tests require very little preparation beforehand.  Depending on the amount of blood required for the test, blood can be drawn from a vein, artery or skin puncture. Obtaining a blood sample only takes about five minutes, and most patients find blood tests to be nearly painless.

A blood test uses a sample of blood to analyze various substances in the blood. Physicians 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 or diseases, including those related to the digestive system. Blood tests may be used t

• 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

Digestive conditions that may be diagnosed through blood tests include:

• Acute pancreatitis. Inflammation of the pancreas, which may be detected with blood tests that reveal several abnormalities. These include elevated levels of the pancreatic enzymes amylase and lipase, elevated white blood cell count, elevated liver enzymes and bilirubin, high blood sugar (hyperglycemia) and low calcium levels.
  

  

• Appendicitis. A high white blood cell count may indicate an infection resulting from an inflammation of the appendix.
  

  

• Cancer. Elevated protein levels, which may indicate certain cancers of the digestive system (e.g., cancers of the colon, gallbladder, liver, pancreas) can be detected with blood tests.
  

  

• Celiac disease. Disorder in which the patient cannot tolerate wheat protein (gluten). A blood test can detect the presence of certain antibodies associated with this disease, including anti-gliadin, anti-endomysium and anti-tissue transglutaminase.
  
  
• Cholecystitis. Condition in which the wall of the gallbladder becomes inflamed. A blood test that detects elevated levels of white blood cells may indicate the presence of cholecystitis.
  
   
• Cirrhosis. Scarring of the liver, which can be detected by certain blood tests that reflect loss of liver function and changes in tissue (fibrosis).
  
  
• Diverticulitis. A high white cell count may indicate this inflammation of a diverticulum, an abnormal pouch in the digestive tract.
  
  
• Gastritis. The presence of Helicobacter pylori (H. pylori) antibodies may indicate past or present infection with H. pylori bacteria, which can cause this inflammation of the stomach lining and peptic ulcers.
  
  
• Hemochromatosis. Two blood tests can be used to detect this disorder, which interferes with iron metabolism and causes excess iron deposits throughout the body, leading to liver disease. A serum transferrin saturation test measures the amount of iron bound to the protein transferrin, which carries iron in the blood. A serum ferritin test measures the amount of iron stored in the body.
  

  

• Hepatitis. High levels of bilirubin and the enzyme aminotransferases may indicate the presence of this inflammation of the liver. There are several types of hepatitis, and various other blood tests may be performed to help determine the exact nature of a hepatitis infection. A new blood test, which both screens for hepatitis B and confirms its presence, was recently approved by the U.S. Food and Drug Administration.
  
  
• Inflammatory bowel disease. Blood tests can help detect anemia or infection, two symptoms associated with Crohn’s disease, a chronic and progressive inflammation of the ileum, or ulcerative colitis, a chronic inflammatory disease of the large intestine and rectum. Blood tests can also reveal the presence of certain antibodies, which fight foreign substances in the body, and may signal the presence of these diseases.
  
  
• Peptic ulcer. As with gastritis, blood tests can be used to detect the presence of H. pylori antibodies that may indicate past or present infection with this bacteria, which can cause peptic ulcers.
  
  
• Peritonitis. Inflammation or infection of the peritoneum, a membrane that lines the abdominal cavity and organs. Blood testing may be performed to check for an elevated white blood cell count, which may indicate infection.
  
  
• Wilson's disease. This disorder is marked by an accumulation of copper in the body. Blood tests can reveal the amount of copper and ceruloplasmin (glycoprotein to which copper is bound) in the blood.

Blood tests may also be used to detect malabsorption (inability of the body to absorb nutrients), which is associated with a number of digestive disorders.

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

• Vein puncture. 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. 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)

Many types of tests may be used to diagnose or rule out digestive conditions and diseases, including:

• Basic metabolic panel (BMP). A group of tests often ordered in hospital emergency rooms because their components provide important information about the status of a patient’s kidneys, electrolyte and acid/base balance. They also reveal a patient’s blood glucose (sugar) levels. Significant changes in these test results can indicate acute conditions, such as kidney failure, insulin shock or diabetic coma, respiratory distress or heart rhythm changes.
  
  
• Complete blood count (CBC). Measures the number of red blood cells, white blood cells and platelets in a patient’s blood. It also detects the amount of hemoglobin (a substance that carries oxygen throughout the body) in the red blood cells and a number of other factors. This test can detect conditions such as anemia that may be associated with digestive disorders such as inflammatory bowel disease. It may also be used to detect conditions such as pancreatitis.  Patients who take medications that affect the CBC must have periodic blood testing for monitoring.
  
  
• Differential. Also called white blood cell count (WBC), it 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 may increase as a result of infection (e.g., appendicitis) or decrease with use of certain medications or in response to certain diseases. In addition, a low WBC indicates that a patient may be at higher risk for infections.
  
  
• Complement. Measures the blood levels of proteins (complement) that help destroy foreign substances in the body. This type of blood test is also useful in evaluating kidney damage and in monitoring the progression of a disease.
  
  
• 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 somewhere in the body.
  
  
• Electrolyte panel. Measures the body’s main electrolytes (sodium, potassium, chloride and carbon monoxide) to help determine whether or not the body has a proper fluid balance. Patients with persistent diarrhea or nausea are at risk for dehydration and may receive electrolyte panel testing.
  
  
• 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.
  
  
• Enzyme tests. A group of blood tests that measure enzyme (protein 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. These tests may be used to measure liver or pancreas function and can help identify conditions such as pancreatitis.
  
  
• Antibody tests. Blood tests are available for many antibodies, substances produced by the body to fight specific infections. The presences of some antibodies are general indicators of inflammation somewhere in the body. Other antibodies may more specifically indicate diseases. For example, two different antibodies usually identify the two types of inflammatory bowel disease: Crohn's disease and ulcerative colitis.

Some blood testing requires little or no preparation to achieve an accurate result. However, in other cases patients may need to fast or avoid certain substances to ensure that certain factors do not skew test results. For example, patients may just need to reduce or stop the use of certain medications (including herbal remedies) and/or vitamins at some point prior to the test.

Additionally, exercise and alcohol and caffeine consumption may be temporarily restricted or suspended prior to a blood test. Other factors known to potentially alter the results of some blood tests include dehydration, excessive eating or recent sexual activity.

Blood tests are performed in physicians’ offices, hospitals and in separate medical offices or laboratories. 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 a simple and nearly painless process for most people. If the test only requires a drop or two of blood, a prick of the finger, earlobe or heel (in the case of babies) 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 not usually 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. First, the technician cleans the area - usually the inside of the elbow or the back of the hand - with rubbing alcohol. Then a wide elastic band or piece of latex tubing may be tightened around the upper arm to slightly increase pressure in the vein. Next, 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. If blood must be taken from an artery instead of a vein, it is usually drawn from a small artery located on the inside or the top of the wrist.

The precise amount of blood to be drawn is determined by the type and number of tests scheduled. Usually, it is around one-fourth of an ounce (7 milliliters). The technician may change test tubes more than once during 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 prevents glucose (blood sugar) 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.

Following the withdrawal of blood, patients may resume medications and food intake according to their physician’s instructions. 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.

Blood 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 a disease or health problem, their blood test 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 the normal range, the test may be repeated to verify results or additional tests may be ordered to determine the underlying cause(s) of 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 useful in the diagnosis of many digestive conditions or diseases, other diagnostic tests are usually performed to confirm the results. These may include imaging tests such as x-rays, bone scans or computed axial tomography (CAT) scans, urine tests and other procedures, such as:

• Fecal tests. Samples of the patient’s stool are examined for evidence of blood or signs of disease, such as parasites or bacteria.
  
  
• Endoscopy. A flexible tube with a camera is inserted into the body to examine hollow spaces, such as the stomach. Other types of endoscopies include:
  
  
• • Colonoscopy. Examination of the entire colon with a long tube and camera that is inserted into a patient’s rectum.
    
    
  • Flexible sigmoidoscopy exam. Similar to a colonoscopy, this procedure uses a shorter tube to investigate the lower parts of the colon (sigmoid colon and descending colon). In some cases, this test will be performed in conjunction with a fecal occult blood test.
    
    
• Upper GI barium tests and lower GI barium tests. A contrast medium called barium is introduced into the patient, through the rectum for a lower GI and usually as a liquid that is swallowed for an upper GI. X-ray images will show the barium in the different parts of the digestive system and can help identify abnormalities such as polyps.
  

  

• Biopsy. A tissue sample may be removed and analyzed to determine whether or not it is cancerous.

There are 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. Applying warm compresses to the spot several times daily can help reduce swelling.

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

1. Which digestive conditions can be detected with this blood test?
   
   
2. Which digestive condition do you suspect that I may have?
   
   
3. Can I eat before the test or do I have to fast for a certain period of time beforehand?
   
   
4. How else should I prepare for the test?
   
   
5. Will the test be painful?
   
   
6. How many vials of my blood are needed for this test?
   
   
7. Are there any significant risks associated with the test?
   
   
8. Can the test have any side effects that I should report immediately to you, such as swelling at the injection site?
   
   
9. How long will I have to wait for results?
   
   
10. Will I need additional tests to confirm diagnosis?