Investigation of persistent diarrhoea

Article from one of last year’s BJGPs, summarising the BSG guidance on investigation of persistent diarrhoea, as updated in April 2018:


Types 5 – 7 on Bristol stool chart, with increased frequency, for >4 weeks, different from normal.


Much of it is what I’d do anyway; FBC, CRP, coeliac screen, stool culture. They also list TFTs, which I’m more dubious about; I’m curious as to how often thyrotoxicosis would show up purely as chronic diarrhoea without any other symptoms, and the chance of picking up a case of thyrotoxicosis that would otherwise be missed does have to be weighed against the risk of overdiagnosis and overtreatment. But, anyway, it’s on there. (I’ve since found out that it’s also on the list of tests our local system requires us to have checked before checking a faecal calprotectin, so it’s one I’ll have to include in investigations for the foreseeable future.)

They don’t list PV/ESR, which interested me. Maybe this is also an overtreatment thing?

However, there are a few more tests:

  • Faecal calprotectin. (Misspelled as ‘faecal calprotection’ in their flowchart, BTW, so I think the authors’ spellcheck might have been getting overenthusiastic; anyway, I double-checked the spelling for myself.) This detects inflammation within the gut, and is useful in cases where cancer is not suspected. The guidelines recommend that FCP be requested if the person is <40 yrs and cancer is not suspected. <50 mcg/g is reassuring, >250 mcg/g is suspicious of IBD, and anything in between is borderline; consider repeats/further investigations according to symptoms.
  • Faecal immunochemical testing. This detects the presence of blood in faeces, and has a ‘better diagnostic performance’ than FOBT. It’s recommended in cases where malignancy is suspected and there is no rectal bleeding, as a ‘rule-out’ test to guide further investigations.
  • HIV testing/immunoglobulins. Always bear in mind that immunodeficiencies can cause chronic diarrhoea, so consider the possibility and whether a test should be offered.
  • Cryptosporidium. Following on from the above, in patients who are immunodeficient, it’s worth asking for this on a stool test.

EDITED: We’ve just had a letter through from the lab mentioning the interpretation of faecal calprotectin, which mentions:

  1. It can be used in patients 16 – 45 yrs.
  2. If the level is >250 mcg/g in a patient in whom IBD is suspected, refer urgently. If it’s 50 – 250, repeat in 6 weeks if other causes excluded.
  3. Polyps and coeliac disease can cause raised FCP. So can NSAIDs, gastroenteritis, diverticulitis.

There are also some new recommendations in secondary care. A surprisingly high proportion of patients with diarrhoea-predominant IBS actually have bile salt malabsorption, so this should now be tested for (or sequestrants trialled empirically if testing is unavailable). Elderly patients with faecal incontinence should be offered anorectal manometry and endoanal ultrasonography. (On this subject; always remember the possibility of faecal impaction with overflow.)

Note that diarrhoea due to hormone-secreting tumours is rare. The recommendation is that these be tested for only after other causes of diarrhoea have been excluded; therefore, I shouldn’t be ordering any urinary 5-HIAAs on people with chronic diarrhoea.


About Dr Sarah

I'm a GP with a husband and two young children.
This entry was posted in Credits 2020, Gastroenterology. Bookmark the permalink.

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