Diagnosis of Food Poisoning

Most times, the diagnosis of food poisoning is made by history and physical examination. Often, the patient volunteers the diagnosis when they come for medical care. For example, "I got sick after eating potato salad at a picnic" or "I drank a raw egg protein shake". 

Routine blood tests are not usually ordered unless there is concern about something more than the vomiting and diarrhea. In patients with significant dehydration, the health care professional may want to check electrolyte levels in the blood as well as kidney function. If there is concern about hemolytic uremic syndrome, a complete blood count (hemogram, CBC) to check the red blood cells, white blood cells, and platelet count may be ordered. If there is concern about hepatitis, liver function tests may be ordered.

Stool samples may be useful especially if there is concern about infections caused by Salmonella, Shigella and Campylobacter, the common non traveler's diarrhea. This is especially true when the patient presents with bloody diarrhea, thought to be due to infection. If there is concern about a parasite infection, stool samples can be examined also for the presence of parasites. Some parasites may be very difficult to see under the microscope, including Cyclospora, because it is so tiny.

Depending on the suspected cause of the food poisoning, there are some immunological tests (for example, detection of Shiga toxins) that the CDC recommends. Cyclospora DNA may be detected in the stool using molecular testing called polymerase chain reaction (PCR). Other methods may be used (for example, detection of prions in tissue samples).