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The difference between diarrhoea and dysentery is quite clear; but the appearance of blood in stool or bloody diarrhoea is a very confusing term when compared with dysentery. Are they different in the amount of blood or their etiology or pathogenesis or something else. I searched a lot in the internet and medicine and pathology books but nowhere I could find a straight answer. If anyone knows about it please reply with proper reference and values (if its about the amount).

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  • $\begingroup$ I think dysentery is always associated with infection but bloody diarrhoea can happen because of many other aetiological reasons. (Although, etymologically, dysentery just means an upset gut). $\endgroup$ – WYSIWYG Sep 2 '16 at 8:44
  • $\begingroup$ I am not too sure that's why I am commenting. I'll verify if this is true and then post as an answer. $\endgroup$ – WYSIWYG Sep 2 '16 at 10:36
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Diarrhoea
Diarrhea is loosely defined as passage of abnormally liquid or unformed stools at an increased frequency. For adults on a typical Western diet, stool weight >200 g/d can generally be considered diarrheal. Diarrhea may be further defined as acute if <2 weeks, persistent if 2–4 weeks, and chronic if >4 weeks in duration.
~Harrison's principles of internal medicine, 20$^{th}$ edition, page 261.

Dysentry
Dysentery is bloody diarrhoea, i.e. any diarrhoeal episode in which the loose or watery stools contain visible red blood. Dysentery is most often caused by Shigella species (bacillary dysentery) or Entamoeba histolytica (amoebic dysentery).
~WHO definition

One can also follow WHO definition of diarrhea for practical purposes but still I mentioned it from Harrison as it is more specific and quantified.

'Blood in stools' generally describe visible blood in stool, and the quantity of stool passed here can be normal like in upper GI bleeding if compared to diarrhoea or dysentry.

Diarrhoea can be classified into four major categories: Secretory, Osmotic, Malabsorbtive, and Exudative, in which exudative diarrhoea show such features of bloody stool.(~ Robbins basic pathology 9$^{th}$ edition page 577).

In fact, it is also clearly mentioned in Harrison in the topic of diarrhoea that:-

Invasive bacteria and Entamoeba histolytica often cause bloody diarrhea (referred to as dysentery).

Conclusively, bloody diarrhoea and dysentry are the same.

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  • $\begingroup$ If anyone thinks that there is some issue with this answer please do suggest me by commenting on it, this will help me to improve writing posts next time. $\endgroup$ – Sikander Aug 2 at 14:55

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