The inside poop on abnormal stool movements

Why you should look before you flush

Published: November 06, 2014 05:00 PM

The 52-year-old truck driver in my office had rushed in a few minutes earlier. He had passed a large black stool (well known as an indicator of internal bleeding) and feared the worst. A test for the presence of blood was negative, so I proceeded to ask him my usual questions about abnormal bowel movements.

Had he taken anything containing bismuth, such as Pepto-Bismol, to settle an upset stomach? Was he taking iron supplements? Did he eat a lot of beets, blueberries, or caviar? His answer was “no” to each, but then he volunteered the following: “Could it have been the squid-ink pasta I ate last night?” Yes!

I added squid-ink pasta  to my growing list of substances that cause non-worrisome dark stools.

That case ended happily, but the result could just as well have been other­wise. Had that black stool actually contained blood, his observation might have been lifesaving, leading to early treatment of whatever the cause was.

It may not be the most pleasant task, but checking your stool is important because changes in its shape, consistency, or color could be a sign of an underlying condition, and your description could help your doctor diagnose the cause. If you notice any of the warning signs below, give your doctor a call.  

A guide to problem stools

If it floats

Most stools sink. But if they contain fat they might float, or you may see actual fat droplets on the water’s surface. A lack of pancreatic enzymes may be to blame. That can occur as a result of chronic inflammation of the pancreas, or following its removal. It could also be a sign of intestinal malabsorption from diseases that affect the intestinal wall, such as celiac disease. The prescription weight-loss drug Xenical or its over-the-counter version, Alli, can also cause fatty stools because they block fat absorption to some degree.

If it's pencil-thin

The occasional thinner-than-normal stool is usually not a concern. But repeated pencil-thin ones indicate something is obstructing or constricting the rectum. Such narrowing can result from spasm of the rectal wall due to internal hemorrhoids, inflammation from radiation treatments, or colitis. A very enlarged prostate might also narrow the passageway; a cancer in the rectum is also a possibility.

If it's the color of pale clay

Bile made by the liver and concentrated in the gall bladder is responsible for the medium-brown color of normal stool. A lack of color implies some blockage of the flow of bile from the liver to the intestine. The culprit could be a gallstone blocking the bile duct. Other causes include hepatitis and cancer of the bile ducts or the pancreas.

If it has mucus in it

A small amount of visible mucus in stool is normal (the clear jellylike substance is found through­out the digestive tract). But stool containing large globs of mucus points to a problem. That could be an indicator of an inflammatory bowel disease, such as mucus colitis, or it could indicate a mucus-secreting intestinal polyp.

If it's mushy, pasty, and similar to diarrhea

Mushy or watery stools that come with frequent trips to the toilet—and are often accompanied by fever—are typical signs of infection with Clostridium difficile. C. diff is a bacteria that lives in many people’s intestines, where it is usually kept in check by other intestinal bacteria. But a prolonged course of antibiotics—especially broad spectrum ones such as clindamycin (Cleocin and generic)—can kill off those other intestinal bacteria, allowing C. diff to grow out of control. C. diff releases a toxin that attacks the intestinal wall, and if left untreated, it can be life-threatening. Metronidazole (Flagyl and generic) or vancomycin (Vancocin and generic) are required to quell the super­infection. Even so, there is a substantial recurrence rate.  

Marvin Lipman, M.D.

Chief Medical Adviser and Medical Editor
Editor's Note:

This article also appeared in the October 2014 issue of Consumer Reports on Health.

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