Critical evaluation of a CLIA-waived streptococcal antigen detection test in the emergency department

Study objective: We compare the performance of a Clinical Laboratory Improv ement Amendments (CLIA)-waived antigen detection test (ADT) analyzed in the emergency department and a CLIA moderately complex ADT performed in the ho spital microbiology laboratory. Methods: Samples from throat swabs were obtained using a double-headed Cult urette II (Becton Dickinson Medical Systems, Sparks, MDI from a consecutive sample of 322 patients 3 years or older who presented to the ED of a unive rsity-affiliated pediatric referral hospital with the complaint of sore thr oat during 1998. One swab was transported to the microbiology laboratory an d analyzed using a CLIA moderately complex ADT; negative results were confi rmed using sheep blood agar culture. The second swab remained in the ED whe re a nurse conducted a CLIA-waived ADT The accepted standard for documentat ion of group A beta -hemolytic streptococcal (GABHS) infection was either a positive moderately complex ADT or culture result. The time of specimen co llection, as well as the time the ED results and microbiology laboratory re sults were available to treating physicians, were recorded. Main outcome me asures were concordance (kappa statistic), sensitivity, and turnaround time (Mann-Whitney U test). Results: Three hundred twenty-two patients (mean age 7.5 years) had both AD Ts performed. One hundred one (31%) patients had documented GABHS in the mi crobiology laboratory; 83 (82%) had a positive ADT result in the microbiolo gy laboratory, and 18 (18%) had a positive culture result after a negative moderately complex ADT result. In 299 patients or 93% (95% confidence inter val [CI] 90.8%, 95.8%) of patients, the waived ADT and the moderately compl ex ADT results were concordant (kappa 0.82; 95% CI 0.78, 0.86; P<.001). The sensitivity of the waived ADT was 80%; the sensitivity of the moderately c omplex ADT approximated 82% (difference of 2%; 95% CI -3%, 7%). The median times from swab specimen collection to availability of ADT results were 10 minutes (range 3 to 37 minutes) far the waived ADT and 35 minutes (range 5 to 262 minutes) for the moderately complex ADT (P<.001) with a difference o f 25 minutes (95% CI 22.4, 27.6 minutes). Conclusion: In this study, an ED CLIA-waived rapid streptococcal throat tes t performed as well as its equivalent CLIA-regulated laboratory test. Furth er, the ED test provided results more rapidly than the laboratory test. Our results also Validate previous work that negative rapid throat test result s in pediatric patients in the ED should be confirmed by standard throat cu lture.