Conjunctivitis laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Sara Mehrsefat, M.D. [2]
Overview
Laboratory tests are not often required as conjunctivitis is often treated empirically. Obtaining conjunctival cultures is generally reserved for cases of suspected infectious neonatal conjunctivitis, recurrent conjunctivitis, conjunctivitis recalcitrant to therapy, conjunctivitis presenting with severe purulent discharge, and cases suspicious for gonococcal or chlamydial infection.
Laboratory Findings
Laboratory tests usually are not required in patients with mild conjunctivitis of suspected viral, bacterial or allergic origin. However, specimens for bacterial cultures should be obtained in patients who have severe inflammation (hyperacute purulent conjunctivitis) or chronic or recurrent conjunctivitis. Cultures also should be obtained in patients who do not respond to treatment.
Viral Conjunctivitis
Laboratory studies for viral conjunctivitis should include the following:
- Rapid antigen testing for adenoviruses (can identify the viral causes of conjunctivitis and prevent unnecessary antibiotic use)
Bacterial Conjunctivitis
Acute bacterial conjunctivitis is usually self-limited and laboratory tests usually are not required. Swabs for bacterial culture is generally reserved for cases of suspected infectious neonatal conjunctivitis (ophthalmia neonatorum), recurrent conjunctivitis, conjunctivitis recalcitrant to therapy, conjunctivitis presenting with severe purulent discharge, and cases suspicious for gonococcal or chlamydial infection.
Chlamydial Infection
Laboratory studies for chlamydial conjunctivitis should include the following:
- Conjunctival scraping for DNA hybridization assays
- Conjunctival scraping for Polymerase chain reaction (PCR)
- Cytology scrapings for gram staining and/or giemsa staining (help characterize the conjunctival inflammatory response and rarely done because of the cost and the general lack of laboratory staff experienced in handling ocular specimens)
- Direct fluorescent monoclonal antibody staining of smears
- Enzyme immuno-assays for Chlamydia organisms
Gonococcal Infection
Laboratory studies for chlamydial conjunctivitis should include the following:
- Immediate Gram staining of specimens for gram-negative intra-cellular diplococci
- Special cultures for neisseria species on chocolate agar or Thayer-Martin
Neonatal Conjunctivitis
Laboratory studies for neonatal conjunctivitis should include the following:
- Cytology scrapings for gram staining and/or giemsa staining
- Conjunctival scraping for Polymerase chain reaction (PCR) for chlamydia, gonorrhea, and HSV
- Special cultures for neisseria species on chocolate agar or Thayer-Martin
- Culture on blood agar
- Culture of corneal epithelial cells for HSV (cornea is involvement)
Allergic Conjunctivitis
Most cases are mild, and the patient just needs reassurance. Laboratory studies for allergic conjunctivitis should include the following:
- Superficial conjunctival scrapings may reveal eosinophils (severe cases)
- Measurement of tear levels of various inflammatory mediators (such as IgE, histamine, and tryptase)
- Skin testing by an allergist (may provide definitive diagnosis)
Keratoconjunctivitis Sicca
Keratoconjunctivitis sicca, is essentially a clinical diagnosis, made by combining information obtained from the history, physical examination and performing one or more diagnostic tests to lend additional objectivity to the diagnosis. Laboratory studies for keratoconjunctivitis sicca should include the following:
- Decreased corneal sensation can be measured using a cotton tip applicator or more precisely with a Cochet-Bonnet esthesiometer. Sensory denervation may cause dry eye by reducing the afferent signaling of tear production, reducing the blink rate, and by altering trigeminal nerve influences on ocular epithelial health. Decreased corneal sensation can also result from chronic dry eye.
- Measurement of tear breakup time (TBUT),
- the Schirmer test
- Analysis of tear proteins or tear-osmolarity (TFO)
- Tear film interferometry (measure lipid layer thickness)
- Serology for circulating autoantibodies may be indicated:
- Antinuclear antibody|Antinuclear antibody (ANA)]]
- Rheumatoid factor (RF)
- Anti-Ro (SS-A) antibody
- Anti-La (SS-B) antibody
Conjunctival incisional biopsy is occasionally done when granulomatous diseases (e.g., sarcoidosis) or dysplasia are suspected.