Diagnosis and Tests for Diphtheria

Diphtheria is one of the few diseases where doctors are taught to act first and confirm later. When the classic picture is there - a grey membrane that bleeds when touched, a swollen "bull neck", hoarseness or noisy breathing - treatment with antitoxin begins on suspicion alone, because waiting for lab results costs lives.

How the diagnosis is made:

• Clinical examination. The pseudomembrane is so characteristic that an experienced doctor often suspects diphtheria the moment the throat is examined. The membrane's grey colour, its tight adherence and the bleeding when scraped set it apart from ordinary tonsillitis.
• Throat and membrane swabs. Swabs from beneath the membrane are sent for smear and culture. Special stains (Albert's stain) show the bacteria's typical appearance within hours, but this alone cannot prove the strain makes toxin.
• Toxigenicity testing. Culture confirmation plus a toxin test (classically the Elek test, or PCR detecting the toxin gene) confirms the case. This usually takes days, which is exactly why treatment cannot wait for it.
• Heart monitoring. An ECG is done early and repeated, because myocarditis can develop silently. Changes on the ECG often precede symptoms of heart damage.
• Blood tests and supportive workup to assess severity and organ involvement.

Conditions that can look similar include streptococcal tonsillitis, infectious mononucleosis (glandular fever), severe oral thrush and epiglottitis. The grey, adherent, bleeding membrane is the feature that points to diphtheria.

Diphtheria is also a notifiable disease in India: a confirmed or suspected case must be reported to public health authorities, who trace and protect contacts.