This is a medical question of type : exams and tests 
 How to diagnose Microscopic Colitis: Collagenous Colitis and Lymphocytic Colitis ? 
 A pathologista doctor who specializes in examining tissues to diagnose diseasesdiagnoses microscopic colitis based on the findings of multiple biopsies taken throughout the colon. Biopsy is a procedure that involves taking small pieces of tissue for examination with a microscope. The pathologist examines the colon tissue samples in a lab. Many patients can have both lymphocytic colitis and collagenous colitis in different parts of their colon.
                
To help diagnose microscopic colitis, a gastroenterologista doctor who specializes in digestive diseasesbegins with
                
- a medical and family history  - a physical exam
                
The gastroenterologist may perform a series of medical tests to rule out other bowel diseasessuch as irritable bowel syndrome, celiac disease, Crohns disease, ulcerative colitis, and infectious colitisthat cause symptoms similar to those of microscopic colitis. These medical tests include
                
- lab tests  - imaging tests of the intestines  - endoscopy of the intestines
                
Medical and Family History
                
The gastroenterologist will ask the patient to provide a medical and family history, a review of the symptoms, a description of eating habits, and a list of prescription and over-the-counter medications in order to help diagnose microscopic colitis. The gastroenterologist will also ask the patient about current and past medical conditions.
                
Physical Exam
                
A physical exam may help diagnose microscopic colitis and rule out other diseases. During a physical exam, the gastroenterologist usually
                
- examines the patients body  - taps on specific areas of the patients abdomen
                
Lab Tests
                
Lab tests may include
                
- blood tests  - stool tests
                
Blood tests. A blood test involves drawing blood at a health care providers office or a commercial facility and sending the sample to a lab for analysis. A health care provider may use blood tests to help look for changes in red and white blood cell counts.
                
- Red blood cells. When red blood cells are fewer or smaller than normal, a person may have anemiaa condition that prevents the bodys cells from getting enough oxygen.  - White blood cells. When the white blood cell count is higher than normal, a person may have inflammation or infection somewhere in the body.
                
Stool tests. A stool test is the analysis of a sample of stool. A health care provider will give the patient a container for catching and storing the stool. The patient returns the sample to the health care provider or a commercial facility that will send the sample to a lab for analysis. Health care providers commonly order stool tests to rule out other causes of GI diseases, such as different types of infectionsincluding bacteria or parasitesor bleeding, and help determine the cause of symptoms.
                
Imaging Tests of the Intestines
                
Imaging tests of the intestines may include the following:
                
- computerized tomography (CT) scan  - magnetic resonance imaging (MRI)  - upper GI series
                
Specially trained technicians perform these tests at an outpatient center or a hospital, and a radiologista doctor who specializes in medical imaginginterprets the images. A patient does not need anesthesia. Health care providers use imaging tests to show physical abnormalities and to diagnose certain bowel diseases, in some cases.
                
CT scan. CT scans use a combination of x rays and computer technology to create images. For a CT scan, a health care provider may give the patient a solution to drink and an injection of a special dye, called contrast medium. CT scans require the patient to lie on a table that slides into a tunnel-shaped device where the technician takes the x rays.
                
MRI. MRI is a test that takes pictures of the bodys internal organs and soft tissues without using x rays. Although a patient does not need anesthesia for an MRI, some patients with a fear of confined spaces may receive light sedation, taken by mouth. An MRI may include a solution to drink and injection of contrast medium. With most MRI machines, the patient will lie on a table that slides into a tunnel-shaped device that may be open ended or closed at one end. Some machines allow the patient to lie in a more open space. During an MRI, the patient, although usually awake, must remain perfectly still while the technician takes the images, which usually takes only a few minutes. The technician will take a sequence of images to create a detailed picture of the intestines. During sequencing, the patient will hear loud mechanical knocking and humming noises.
                
Upper GI series. This test is an x-ray exam that provides a look at the shape of the upper GI tract. A patient should not eat or drink before the procedure, as directed by the health care provider. Patients should ask their health care provider about how to prepare for an upper GI series. During the procedure, the patient will stand or sit in front of an x-ray machine and drink barium, a chalky liquid. Barium coats the upper GI tract so the radiologist and gastroenterologist can see the organs shapes more clearly on x rays. A patient may experience bloating and nausea for a short time after the test. For several days afterward, barium liquid in the GI tract causes white or light-colored stools. A health care provider will give the patient specific instructions about eating and drinking after the test. More information is provided in the NIDDK health topic, Upper GI Series.
                
Endoscopy of the Intestines
                
Endoscopy of the intestines may include
                
- colonoscopy with biopsy  - flexible sigmoidoscopy with biopsy  - upper GI endoscopy with biopsy
                
A gastroenterologist performs these tests at a hospital or an outpatient center.
                
Colonoscopy with biopsy. Colonoscopy is a test that uses a long, flexible, narrow tube with a light and tiny camera on one end, called a colonoscope or scope, to look inside the rectum and entire colon. In most cases, light anesthesia and pain medication help patients relax for the test. The medical staff will monitor a patients vital signs and try to make him or her as comfortable as possible. A nurse or technician places an intravenous (IV) needle in a vein in the arm or hand to give anesthesia.
                
For the test, the patient will lie on a table while the gastroenterologist inserts a colonoscope into the anus and slowly guides it through the rectum and into the colon. The scope inflates the large intestine with air to give the gastroenterologist a better view. The camera sends a video image of the intestinal lining to a computer screen, allowing the gastroenterologist to carefully examine the tissues lining the colon and rectum. The gastroenterologist may move the patient several times and adjust the scope for better viewing. Once the scope has reached the opening to the small intestine, the gastroenterologist slowly withdraws it and examines the lining of the colon and rectum again. A colonoscopy can show irritated and swollen tissue, ulcers, and abnormal growths such as polypsextra pieces of tissue that grow on the lining of the intestine. If the lining of the rectum and colon appears normal, the gastroenterologist may suspect microscopic colitis and will biopsy multiple areas of the colon.
                
A health care provider will provide written bowel prep instructions to follow at home before the test. The health care provider will also explain what the patient can expect after the test and give discharge instructions.
                
Flexible sigmoidoscopy with biopsy. Flexible sigmoidoscopy is a test that uses a flexible, narrow tube with a light and tiny camera on one end, called a sigmoidoscope or scope, to look inside the rectum and the sigmoid colon. A patient does not usually need anesthesia.
                
For the test, the patient will lie on a table while the gastroenterologist inserts the sigmoidoscope into the anus and slowly guides it through the rectum and into the sigmoid colon. The scope inflates the large intestine with air to give the gastroenterologist a better view. The camera sends a video image of the intestinal lining to a computer screen, allowing the gastroenterologist to carefully examine the tissues lining the sigmoid colon and rectum. The gastroenterologist may ask the patient to move several times and adjust the scope for better viewing. Once the scope reaches the end of the sigmoid colon, the gastroenterologist slowly withdraws it while carefully examining the lining of the sigmoid colon and rectum again.
                
The gastroenterologist will look for signs of bowel diseases and conditions such as irritated and swollen tissue, ulcers, and polyps. If the lining of the rectum and colon appears normal, the gastroenterologist may suspect microscopic colitis and will biopsy multiple areas of the colon.
                
A health care provider will provide written bowel prep instructions to follow at home before the test. The health care provider will also explain what the patient can expect after the test and give discharge instructions.
                
Upper GI endoscopy with biopsy. Upper GI endoscopy is a test that uses a flexible, narrow tube with a light and tiny camera on one end, called an endoscope or a scope, to look inside the upper GI tract. The gastroenterologist carefully feeds the endoscope down the esophagus and into the stomach and first part of the small intestine, called the duodenum. A small camera mounted on the endoscope transmits a video image to a monitor, allowing close examination of the intestinal lining. A health care provider may give a patient a liquid anesthetic to gargle or may spray anesthetic on the back of the patients throat. A health care provider will place an IV needle in a vein in the arm or hand to administer sedation. Sedatives help patients stay relaxed and comfortable. This test can show blockages or other conditions in the upper small intestine. A gastroenterologist may biopsy the lining of the small intestine during an upper GI endoscopy.