My doctor just told me that white blood cells were found in my stool culture. She explained that I could be treated with antibiotics for inflammation, or I would be scheduled for a scope. I had previously gone to the doctor three times for diarrhea that lasted nine weeks. What exactly does finding white blood cells in a stool culture mean?

J.

There are many causes for acute diarrhea -- diarrhea that starts abruptly and lasts for a few weeks. The most common causes of this type of diarrhea are food poisoning (caused by bacterial toxins), infections, certain medications (such as antibiotics) and inflammatory diseases of the colon. The factors that a doctor considers in determining the cause of a specific patient's diarrhea include whether the person has traveled recently, whether others in the patient's household or workplace are also ill, whether the patient has been using new medications, and whether there are other symptoms that indicate severe infection or inflammation (fever, vomiting, blood in the stool or abdominal pain).

Often a diagnosis cannot be made on the basis of historical facts, so diagnostic testing is done. Tests done directly on the stool often prove very helpful in the evaluation of diarrhea. These include the simple test to look for white blood cells (WBCs) in the stool. WBCs are not normally present in the stool. The presence of these cells indicates that the cause of the diarrhea is one that results in significant inflammation in the colon. Usually such inflammation stems from invasive bacterial infections such as shigella, campylobacter and salmonella. These infections, which can also be diagnosed by stool culture (although this often takes a few days), are treated with antibiotics. Other infectious causes of diarrhea such as noninvasive bacteria (traveler's diarrhea), bacterial toxins (food poisoning) or viruses do not commonly cause WBCs to be found in the stool.

WBCs can also be found in diarrhea caused by inflammatory diseases of the colon (ulcerative colitis or Crohn's colitis). So, further testing may be needed to establish whether the diarrhea is caused by an infection or by colitis. Colonoscopy can help in this regard by allowing the gastroenterologist to examine the lining of the colon and to take tissue specimens if needed.

If your history indicates probable infection, then the doctor may try antibiotics before resorting to colonoscopy. In cases where the diarrhea lasts longer than a few weeks, it is prudent to perform colonoscopy to evaluate for colitis, which can begin as an acute diarrhea but often progresses to a chronic problem.