What tests diagnose 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."
The health-care professional may ask questions about the symptoms, when they started, and how long they have lasted. A review of systems may help give direction as to what type of infection is present. For example, a patient with numbness of their feet and weakness may be asked about whether they have opened any home canned food recently.
Travel history may be helpful to see if the patient had been camping near a stream or lake and the potential for drinking contaminated water, or if they have traveled out of the country recently and have eaten different foods than they normally do, such as raw eggs or wild game.
Physical examination begins with taking the vital signs of the patient (blood pressure, pulse rate, and temperature). Clinical signs of dehydration include dry, tenting skin, sunken eyes, dry mouth, and lack of sweat in the armpits and groin. In infants, in addition to the above, subtle signs of dehydration may include poor muscle tone, poor suckling, and sunken fontanelle.
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).