Greenberg D N, Ascher D P, Yoder B A, Hensley D M, Heiman H S, Keith J F
Department of Pediatrics, Wilford Hall U.S. Air Force Medical Center, San Antonio, Texas.
J Clin Microbiol. 1995 Jan;33(1):193-8. doi: 10.1128/jcm.33.1.193-198.1995.
Latex particle agglutination (LPA) testing for antigen to group B streptococcus (GBS) has been useful in the diagnosis of GBS sepsis in newborns. However, recent reports have demonstrated that the sensitivity of LPA assays may be as low as 27 to 54%. The purposes of the present study were to directly compare the abilities of four urine antigen assays to detect GBS antigen with clinical urine samples from neonates with GBS bacteremia and to evaluate the effect of the urine concentration on the sensitivities and specificities of these assays. Urine samples were collected serially from neonates with blood cultures positive for GBS or on admission from healthy full-term infants. One milliliter of urine was removed, and the remainder was concentrated to a volume of 1 ml. Unconcentrated samples were serially diluted with normal saline and were assayed to determine the highest dilution which would produce a positive test result. The Wellcogen, Bactigen, and Directigen LPA tests and ICON immunoassay were directly compared by using concentrated and unconcentrated urine specimens and urine specimens with known titers. A total of 94 urine specimens, including 61 concentrated and 75 unconcentrated specimens, from bacteremic infants were available for sensitivity testing, and 220 urine specimens from uninfected infants were available for specificity testing. There were significant differences in sensitivity among the four assays when they were performed on concentrated urine specimens, as follows: Directigen, 98%; Bactigen, 92%; ICON, 89%; Wellcogen, 68%. When the assays were performed on unconcentrated urine specimens, the Directigen (84%) and Bactigen (76%) assays were each significantly more sensitive than the ICON (59%) or Wellcogen (43%) assay. All four assays were significantly more sensitive in detecting GBS antigen in concentrated than in unconcentrated urine. The Directigen assay detected antigen in higher dilutions (geometric mean titer, 1:5) than the ICON (1:3), Bactigen (1.2), or Wellcogen (1:1) assay. The specificity was 99.5% for all four assays when concentrated urine was used and for the Bactigen, Directigen, and ICON assays when unconcentrated urine was used; the Wellcogen assay was 100% specific when unconcentrated urine was used. We conclude that there are significant differences in sensitivity but not specificity among the commercially available assays for the detection of GBS antigenuria when concentrated and unconcentrated urine specimens are tested. These differences in sensitivity may affect the abilities of clinicians to accurately diagnose GBS sepsis before culture results are available.
乳胶颗粒凝集试验（LPA）检测B族链球菌（GBS）抗原，在新生儿GBS败血症的诊断中一直发挥着作用。然而，近期报告显示，LPA检测的敏感性可能低至27%至54%。本研究的目的是直接比较四种尿液抗原检测方法检测GBS抗原的能力，使用患有GBS菌血症的新生儿的临床尿液样本，并评估尿液浓缩对这些检测方法敏感性和特异性的影响。从GBS血培养阳性的新生儿或健康足月儿入院时连续采集尿液样本。取1毫升尿液，其余尿液浓缩至1毫升。未浓缩的样本用生理盐水连续稀释，并进行检测以确定产生阳性检测结果的最高稀释度。通过使用浓缩和未浓缩的尿液标本以及已知滴度的尿液标本，直接比较Wellcogen、Bactigen和Directigen LPA检测以及ICON免疫测定。共有94份来自菌血症婴儿的尿液标本，包括61份浓缩标本和75份未浓缩标本，可用于敏感性检测，220份来自未感染婴儿的尿液标本可用于特异性检测。当对浓缩尿液标本进行检测时，四种检测方法在敏感性上存在显著差异，具体如下：Directigen为98%；Bactigen为92%；ICON为89%；Wellcogen为68%。当对未浓缩尿液标本进行检测时，Directigen检测（84%）和Bactigen检测（76%）的敏感性均显著高于ICON检测（59%）或Wellcogen检测（43%）。所有四种检测方法在检测浓缩尿液中的GBS抗原时比未浓缩尿液更敏感。Directigen检测在比ICON检测（1:3）、Bactigen检测（1:2）或Wellcogen检测（1:1）更高的稀释度（几何平均滴度为1:5）下检测到抗原。当使用浓缩尿液时，所有四种检测方法的特异性均为99.5%；当使用未浓缩尿液时，Bactigen、Directigen和ICON检测的特异性为99.5%；当使用未浓缩尿液时，Wellcogen检测的特异性为100%。我们得出结论，当检测浓缩和未浓缩尿液标本时，市售检测GBS菌尿抗原的方法在敏感性上存在显著差异，但在特异性上无显著差异。这些敏感性差异可能会影响临床医生在获得培养结果之前准确诊断GBS败血症的能力。
