Priority Topic: Diarrhea

Key Feature 5: Pursue investigation, in a timely manner, of elderly with unexplained diarrhea, as they are more likely to have pathology. 
Skill: Clinical Reasoning, Selectivity
Phase: Hypothesis generation, Investigation

When someone comes in with a complaint of acute diarrhea, it's usually a viral gastroenteritis. So we don't necessarily do any tests right away if the patient looks well and doesn't have risk factors. That being said, if a patient appears unwell or with risk factors for more serious underlying disease, doing some investigations sooner rather than later is warranted. What are the indications for performing investigations in the setting of acute diarrhea?

If a patient appears dehydrated then ordering a set of electrolytes and a creatinine would be useful to look for complications of the diarrhea, regardless of the etiology. A CBCd may be ordered as a nonspecific marker of disease severity if this is something that may be monitored, say in a patient who is being admitted.

Indications for first-line microbiological testing to look for an underlying infectious pathogen for the diarrhea include:

1. Stool culture & sensitivity 
   1. If there is severe illness, defined by having at least one of the following:
      1. Profuse watery diarrhea with signs of hypovolemia
         
      2. Passage of at least 6 unformed stools in past 24 hrs
         
      3. Severe abdominal pain
         
      4. Need for hospitalization
   2. If there is suspicion of inflammatory diarrhea, by at least one of the following features:
      
      1. Bloody diarrhea*
         
      2. Passage of many small volume stools containing blood and mucus
         
      3. Temp of at least 38.5
   3. If the patient is high risk, by having at least one of the following features:
      1. 70 years of age or older
         
      2. Comorbidities that may be exacerbated by hypovolemia or rapid infusion of fluid
         
      3. Immunocompromising condition
         
      4. Inflammatory bowel disease
         
      5. Pregnancy
         
   4. If there is a persistence of symptoms for greater than 1 week
   5. If there is a public health concern because they work in one of the following areas:
      1. Food prep
      2. Health care
      3. Day care
2. Stool for C diff toxins if at risk (see a previous post on this)
3. Blood cultures if the patient appears toxic or has a high fever

Imaging would seldom be indicated in the setting of acute diarrhea, but there are 2 reasons for which you may consider getting an imaging study:

1. An abdominal CT scan would be warranted in the patient who is at risk for colonic ischemia (consider this in the elderly patient, for example, if the clinical picture fits the bill)
2. Endoscopy is warranted if suspicious of inflammatory bowel disease, via referral to a gastroenterologist.

*Note that if there is bloody diarrhea, the patient is at risk of having EHEC (Enterohemorrhagic E. coli), and further tests are indicated right off the bat that include: stool culture for EHEC and shiga toxin, and fecal leukocytes or fecal lactoferrin (not available everywhere). Furthermore, if there are ever any pathogens that you are particularly suspicious of, it is a good idea to check with the lab that you are sending the sample to, to see if they test the stool for the bacteria you are suspecting, and it doesn't hurt to write this down on the requisition form as well, as certain organisms are tested for with special techniques, which the lab may not do by default.