Q: What laboratory confirmation tests do you routinely employ when testing for herpes simplex virus and including it in your differential diagnosis?
A: While much of the diagnosis of a patient with herpes simplex is clinical, there are cases in which a laboratory or in-office test can solidify the diagnosis. For example, a patient may present with signs that can indicate herpes simplex, but they may also be indicative of a bacterial, fungal or parasitic infection, says Hank Perry, M.D., of Ophthalmic Consultants of Long Island.
When it comes to herpes simplex, lab tests can help firm up an uncertain diagnosis.
Courtesy: Kim Reed, O.D.
"Sometimes, you'll see an inflammation in the trabeculum, and that causes a trabeculitis," says Dr. Perry. "And, the patient who has a uveal tract inflammation will actually have an increase in trabecular pressure in one eye, and that's strongly suggestive of herpes simplex. But, in these cases, Id still send out for a lab test."
The crucial factor in these cases is that these signs are not diagnostic, but only suggestive. Diagnostic signs include "dendritic figures on the corneal epithelium with characteristic end bulbs. The other characteristic presentation is disciform (round) keratitis, which has corneal edemaand under the areas of edema, the endothelial cells usually have keratic precipitates marking the boundaries of the edema. And of course, injection and decreased visual acuity are associated with that," Dr. Perry says.
There are lab or in-office tests available to help solidify the diagnosis in the event of an unclear presentation. "The enzyme-linked viral inducible system (ELVIS) creates fluorescent antibodies that are absorbed by the viral particles. We then see a positive staining reaction," says Dr. Perry. ELVIS results are available in as little as 24 hours.1
Other tests include complement fixation, where the patient is examined for antibodies for herpes simplex, Dr. Perry says. "We can find out if the titer is rising or falling, because a certain level will indicate an active infection. Or, consider MicroTrak (Trinity Biotech), a direct fluorescent antibodies test, or HerpChek (DuPont), an enzyme immunoassay."
"The gold standard is the polymerase chain reaction (PCR), which seems to be very effective," adds Dr. Perry. "Or, the practitioner can order an actual culture of the viral particles in monkey kidney cells--the timeline for that is about a week, and that's more expensive."
Lab tests may not always be necessary, but do not hesitate to present the option if you think that the findings will benefit your patient. "Most patients have certain signs that make it likely that herpes simplex is the underlying condition," notes Dr. Perry. "In other cases, the difficulty is that practitioners are reluctant to give their patient an extra expense, and they're unsure about telling patients that they're not completely secure in their diagnosis to want the separate test. I think that, once doctors start using these tests, theyll have a better handle on how to manage patients."
1. Slonim CB, Kaufman HE. Herpes simplex virus-induced herpetic keratitis. Ocular Infect Inflam. 2008 Fall; 1(1):3-10.