Food Poisoning Workup

Updated: Jun 19, 2018
  • Author: Roberto M Gamarra, MD; Chief Editor: Praveen K Roy, MD, MSc  more...
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Laboratory Studies

Obtain the following laboratory studies in cases of suspected food poisoning:

  • Gram staining and Loeffler methylene blue staining of the stool for WBCs help to differentiate invasive disease from noninvasive disease.

  • Perform microscopic examination of the stool for ova and parasites.

  • Bacterial culture for enteric pathogens, such as Salmonella, Shigella, and Campylobacter organisms, becomes mandatory if a stool sample shows positive results for WBCs or blood or if patients have fever or symptoms persisting for longer than 3-4 days.

  • Perform blood culture if the patient is notably febrile.

  • CBC with differential, serum electrolyte assessment, and BUN and creatinine levels help to assess the inflammatory response and the degree of dehydration.

  • Assay for C difficile to help rule out antibiotic-associated diarrhea in patients receiving antibiotics or in those with a history of recent antibiotic use.

Histamine food poisoning from gram-negative bacteria in fin-fish products is also common, and Morganella morganii and M psychrotolerans are particularly strong histamine producers. The development of real-time quantitative polymerase chain reaction (RTiqPCR) techniques in conjunction with the use of selective primers and a quantitative enrichment step appear to have the potential to identify and quantify these two species in fish products. [15]


Imaging Studies

Flat and upright abdominal radiographs should be obtained if the patient experiences bloating, severe pain, or obstructive symptoms or if perforation is suggested.



When a stool examination is nondiagnostic, performing sigmoidoscopy/colonoscopy with biopsy and esophagogastroduodenoscopy (EGD) with duodenal aspirate and biopsy may be beneficial. This is especially important in patients who are immunocompromised.

Consider sigmoidoscopy in patients with bloody diarrhea. It can be useful in diagnosing inflammatory bowel disease, antibiotic-associated diarrhea, shigellosis, and amebic dysentery.