Purpose: Family physicians usually diagnose herpes zoster on clinical grounds only, possibly resulting in false-positive diagnoses and unnecessary treatment. We wanted to determine the positive predictive value of the physicians' judgment in diagnosing herpes zoster and to assess the applicability of dried blood spot analysis for diagnosis of herpes zoster in family practice.
Methods: Our study population consisted of 272 patients older than 50 years with herpes zoster (rash for less than 7 days). Dried blood spot samples were collected from all patients and sent by mail to the laboratory. Baseline measurements included clinical signs (localization, severity, and duration of rash) and symptoms (duration and severity of pain). Varicella-zoster virus antibodies were determined at baseline and 5 to 10 days later. Multivariate logistic regression was used to assess independent associations between clinical variables and serological confirmation of herpes zoster.
Results: Dried blood spot analysis was possible in 260 patients (96%). In 236 the diagnosis of herpes zoster was confirmed serologically (positive predictive value of clinical judgment 90.8%; 95% confidence interval, 87.3%-94.3%). Independent clinical variables for serologically confirmed herpes zoster were severity and duration of rash at first examination.
Conclusion: Family physicians have good clinical judgment when diagnosing herpes zoster in older patients. Dried blood spot analysis is a logistically convenient method for serological investigation of patients in family practice, but it is rarely needed for diagnosing herpes zoster.