Doctors may suspect diphtheria in a sick child who has a sore throat with a gray membrane covering the tonsils and throat. Growth of C. diphtheriae in a laboratory culture of material from the throat membrane pins down the diagnosis. Your doctor should notify the laboratory that diphtheria is suspected, because special media are needed for the growth of C. diphtheriae cultures.
Doctors can also take a sample of tissue from an infected wound and have it tested in a laboratory to check for the type of diphtheria that affects the skin (cutaneous diphtheria).
If a doctor suspects diphtheria, treatment begins immediately, even before the results of bacterial tests are available.