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Diagnosis of diphtheria
Last reviewed: 06.07.2025
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The diagnosis of diphtheria is established by a dense whitish-grayish fibrinous film on the mucous membrane of the oropharynx, nose, larynx, etc. With fibrinous inflammation, pain and hyperemia of the mucous membrane are weakly expressed. The lymph nodes are enlarged in accordance with the local process, dense to the touch, moderately painful. Sharp pain when swallowing, bright hyperemia, prolonged fever are not characteristic of diphtheria and indicate against this diagnosis. The severity of edema of the cervical tissue and oropharynx corresponds to the size of the plaque and the degree of general intoxication.
Of the laboratory diagnostic methods, bacteriological testing is of the greatest importance. The material taken with a sterile cotton swab from the site of the lesion is inoculated onto Clauberg's elective blood tellurite medium or its modifications. After growth in a thermostat at a temperature of 37 °C for 24 hours, a bacterioscopic study is carried out. If diphtheria corynebacteria are detected, a preliminary answer is given. The final result of the laboratory test is reported 48-72 hours after studying the biochemical and toxigenic properties of the isolated culture. The study of isolated cultures for toxigenicity is of decisive importance for confirming the diagnosis of diphtheria, especially in doubtful and diagnostically difficult cases.
The toxicity of diphtheria corynebacteria can be determined on guinea pigs, but in practical work at present the determination is carried out on dense nutrient media using the Ouchterlony gel precipitation method.
Specific antibodies in blood serum can be detected using the agglutination reaction (AR), RPGA, ELISA, etc.
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