Investigations
1st investigations to order
stool microscopy, culture, and sensitivity
Test
Useful to delineate causes of diarrhoea and indicated in suspected shigellosis. A positive result is reportable.[5][16][24][28]
The stool sample is suspended in MacConkey agar to identify non-lactose fermenters such as Shigella species.[5] More selective media are then used, after which slide agglutination with Shigella antisera further indicates the likelihood of shigellosis. Biochemical screening tests are confirmatory for species if non-lactose fermenters are found and thought likely to be Shigella on the basis of selective media cultures and slide agglutination. [Figure caption and citation for the preceding image starts]: Stool exudates in a patient with Shigella infectionCDC [Citation ends].
Result
confirmation of Shigella and sensitivities
serum urea and creatinine
Test
Volume depletion may be evidenced by rising serum urea levels. Useful to guide fluid resuscitation, along with clinical findings.
Oligo-anuria and acute renal failure are common clinical findings in haemolytic uraemic syndrome.
Result
serum urea may be increased; renal failure suggests haemolytic uraemic syndrome
FBC
Test
WBC count may not always be elevated and is non-specific. However, leukocytosis may be indicative of septicaemia in severe presentations.
Volume depletion may be evident with rising haematocrit.
Anaemia due to non-immune-mediated haemolysis and thrombocytopenia are features of haemolytic uraemic syndrome.
Result
occasional leukocytosis; possible high haematocrit; thrombocytopenia and anaemia suggest haemolytic uraemic syndrome
Investigations to consider
Shigella serotyping
peripheral blood smear
Test
Used along with clinical findings to detect haemolytic uraemic syndrome.
Result
usually normal; presence of fragmentocytes suggests haemolytic uraemic syndrome
abdominal x-ray
Test
Ordered if toxic dilation or severe colitic process secondary to severe shigellosis is suspected.[28]
Although rare, intestinal necrosis and pancreatic involvement may be seen with haemolytic uraemic syndrome.
Result
markedly dilated colon suggests toxic colon or severe colitis
flexible sigmoidoscopy
Test
Not often required. May be useful to exclude strongly suspected idiopathic inflammatory bowel disease.[28]
Result
normal; ulcers suggest ulcerative colitis
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