Test Catalog

Test ID: CDIP    
Corynebacterium diphtheriae Culture, Varies

Useful For Suggests clinical disorders or settings where the test may be helpful

Confirmation of the clinical diagnosis of diphtheria

Testing Algorithm Delineates situations when tests are added to the initial order. This includes reflex and additional tests.

When this test is ordered, the reflex tests may be performed at an additional charge.

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Corynebacterium diphtheriae is the etiological agent of diphtheria and occurs in 2 forms, respiratory and cutaneous diphtheria. Respiratory diphtheria may be further classified into pharyngeal, tonsillar, laryngeal, and the less common anterior nasal diphtheria. Due to vaccination programs in the United States, diphtheria is now a rarely reported disease. Corynebacterium diphtheriae is primarily spread by droplets from coughing or sneezing. The incubation period averages 2 to 5 days. The illness is characterized by fever, malaise, and sore throat with a distinguishing thick pseudomembrane present over the involved mucosa. A swab from beneath the pseudomembrane is the preferred specimen for culture. The organisms multiplying at the infection site produce a toxin, diphtheria toxin, which may result in systemic complications affecting the heart, nervous system, etc.


In patients with a clinical diagnosis of possible diphtheria, appropriate specimens should be collected for culture; patients should be placed in appropriate isolation and consideration given to administration of empiric antitoxin (available in the United States through the Centers for Disease Control and Prevention) and antibiotics; respiratory and airway support may be required.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

No growth of Corynebacterium diphtheriae

Interpretation Provides information to assist in interpretation of the test results

A positive result supports a diagnosis of diphtheria. The pathogenesis of the associated disease relates to production phage-encoded diphtheria toxin. Since isolates of Corynebacterium diphtheriae may or may not harbor genes to produce the toxin, they should be further tested for diphtheria toxin production. When isolated, other potentially toxin-producing organisms (eg, Corynebacterium ulcerans, Corynebacterium pseudotuberculosis) will also be reported.


A negative result is evidence against a diagnosis of diphtheria but does not definitively rule out this disease since culture may be negative because of prior antimicrobial therapy or organism present below the limit of detection of the assay.

Clinical Reference Recommendations for in-depth reading of a clinical nature

Procop GW, Hall GS, Janda WM, Koneman EW, Schreckenberger PC, Woods GL: Color Atlas and Textbook of Diagnostic Microbiology. 7th ed. In: Wolters Kluwer Health; 2017:890-896