What is the role of lab studies in the diagnosis of proctitis and anusitis?

Updated: Mar 27, 2020
  • Author: David E Stein, MD; Chief Editor: John Geibel, MD, MSc, DSc, AGAF  more...
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In general, for all patients diagnosed with proctitis, a routine workup should be performed to rule out infectious etiologies. The laboratory workup includes stool cultures, ova and parasite analysis, and fecal smears.

In patients at risk, obtain and send an anorectal swab for gonococcal, chlamydial, and herpes simplex viral proctitis. Darkfield microscopy and Venereal Disease Research Laboratory (VDRL)/rapid plasma reagin (RPR) tests should be performed for suspected syphilitic proctitis. Additional tests (eg, polymerase chain reaction [PCR], serologic studies, and nucleic acid amplification tests [NAATs]) may be performed, depending on the suspected etiology.

If the patient is immunocompromised, perform fungal and viral cultures. (Note that fungal and viral anorectal infections are rare in the immunocompetent population.)

Regarding pseudomembranous proctitis or colitis due to C difficile, send the stool for C difficile toxin titers for any patient with a history of current or recent use of antibiotic usage. This must be sent three times to ensure an accurate result; many of the tests have a sensitivity of only 60%. Sending the collection and cultures in accordance with the laboratory specifications is important because the specifications may vary from hospital to hospital.

Entamoeba histolytica is diagnosed by finding the amoeba in the stool; one must send three stool samples for the analysis to be valid. In addition, serologic tests exist, including indirect hemagglutination, indirect electrophoresis, and an enzyme-linked immunosorbent assay (ELISA).

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