Jay W. Marks, MD, is a board-certified internist and gastroenterologist. He graduated from Yale University School of Medicine and trained in internal medicine and gastroenterology at UCLA/Cedars-Sinai Medical Center in Los Angeles.
Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.
What tests are useful in the evaluation of diarrhea?
Acute diarrhea. Acute
diarrhea usually requires few tests.
Measurement of blood pressure in the
upright and supine (lying) positions can demonstrate orthostatic hypotension and
confirm the presence of dehydration. If moderate or severe dehydration or
electrolyte deficiencies are likely, blood electrolytes can be measured.
Examination of a small amount of stool under the microscope may reveal white blood cells indicating that intestinal inflammation is present and prompting further testing, particularly bacterial cultures of stool and examination of stool for parasites.
If antibiotics have been taken within the previous two weeks, stool should be tested for the toxin of
Testing stool or blood for viruses is performed only rarely, since there is no specific treatment for the viruses that cause gastroenteritis.
If there has been recent travel to undeveloped countries or the mountains, stool may be examined under the microscope for Giardia and other parasites.
There are also immunologic tests that can be done on samples of stool to diagnose infection with Giardia.
Chronic diarrhea. With chronic diarrhea, the focus usually shifts from
dehydration and infection (with the exception of Giardia, which occasionally
causes chronic infections) to the diagnosis of
non-infectious causes of diarrhea. (See the prior discussion of common causes of
malabsorption can be diagnosed by measuring the fat in a 72 hour collection of
Sugar malabsorption can be diagnosed by eliminating the offending sugar
from the diet or by performing a hydrogen breath test.
Hydrogen breath testing also can be used to diagnose bacterial overgrowth of the
An under-active pituitary
or adrenal gland and an overactive thyroid gland can be diagnosed by measuring
blood levels of cortisol and thyroid hormone, respectively.
Celiac disease can be
diagnosed with blood tests and a biopsy of the small
Reviewed by William C. Shiel Jr., MD, FACP, FACR on 2/14/2013