Since canker sores can mimic other mouth sores and vice versa, it is important to be sure that the mouth sore that you are dealing with is actually a canker sore. Unfortunately canker sore diagnosis can be a bit challenging, even for dentists and doctors. For an illness that is so common, aphthous ulcers are still a diagnosis of exclusion, that is, the diagnosis is made once other possible causes are ruled out. Fortunately there are a number of factors that can strongly support the diagnosis.

History and physical examination

Canker sore diagnosis rests mostly on the history of the illness and the physical examination of the mouth sores. The diagnosing physician will ask about all canker sore symptoms but also about other diseases and triggers that may have brought on the lesion. The doctor will ask if these mouth sores have ever occurred in the past (since canker sores often recur) and if anyone on the family has had similar mouth lesions. Inciting factors, intensity and quality of the pain, and whether there are any other medical problems that occurred as a result of the possible canker sore will be explored in detail.

The physical examination is usually the most useful and revealing part of the canker sore diagnosis. The physician will look for small red ulcers covered in a gray-yellow coating, possibly encircled in a halo of white or red. She will also identify where in the mouth the lesions occur. There are several visual cues that can help make the physician make the diagnosis.

Blood tests and laboratory studies

There is no specific blood test for a canker sore. Likewise, there is no specific laboratory analysis than can unequivocally make a canker sore diagnosis. Nevertheless, the diagnosing physician will likely take some blood tests to rule out other causes of mouth sores. These tests usually include a complete blood count (measures the number of white blood cells, red blood cells, and platelets in the blood) and a hemoglobin test. Abnormalities in these blood tests may lead to further diagnostic tests. Serum antiendomysium antibody, anti-gliadin antibody and transglutaminase assay may be performed if celiac disease is suspected. Often the blood levels of several key vitamins are measured including Vitamin B₁₂, folate (folic acid), and iron. While a vitamin deficiency does not necessary confirm a canker sore diagnosis, it can be highly suggestive. What is more, once a vitamin deficiency is diagnosed, it is easily corrected.

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Biopsy

A biopsy is a small bit of tissue taken from the body so that it can be studied in a laboratory, usually under a microscope. Taking a biopsy in the course of a canker sore diagnosis is usually, but may occur if the mouth sores are severe or the cause is in question. The biopsy of the canker sore will look abnormal under a microscope but it will not be specific to canker sores. If a biopsy is taken, the pathologist will look for other causes of mouth sores as well. In some cases, the biopsy will include the entire canker sore and also serve as a form of surgical canker sore treatment.

References

Besu I, Jankovic L, Magdu IU, Konic-Ristic A, Raskovic S, Juranic Z. Humoral immunity to cow’s milk proteins and gliadin within the etiology of recurrent aphthous ulcers? Oral Dis 2009;15:560-564.

Scully C, Gorsky M, Lozada-Nur F. The diagnosis and management of recurrent aphthous stomatitis: a consensus approach. J Am Dent Assoc 2003;134:200-207.