Rapid bacterial antigen detection is not clinically useful

Abstract

Latex agglutination (LA) of capsular polysaccharide bacterial antigen is a frequently performed laboratory procedure, but its use is controversial. To assess the clinical utility of this test, we reviewed all LA tests performed over a 10-month period at two sites, a major university-based referral center and a private specialty pediatric hospital. Samples were assayed either individually or as a panel for the group B streptococcus, Streptococcus pneumoniae, Haemophilus influenzae, and three sets of Neisseria meningitidis serogroups (A and Y, C and W135, and B and Escherichia coli K1). Of 5,169 assays performed on 1,268 clinical samples (786 urine and 478 cerebrospinal fluid, 3 pleural fluid, and 1 synovial fluid sample), 57 (1.1%) were positive, including 1.7% of urine and 0.3% of cerebrospinal fluid samples. All LA true-positive cerebrospinal fluid samples showed the causative microorganisms by Gram stain. Detailed chart review of these 57 positive samples showed that the LA result was false-positive in 31 (54%), true-positive in 22 (38%), and indeterminate in 4 (7%) samples. Therapy was not altered on the basis of any of the true-positive LA results. The 31 false-positive results led to additional cost, prolonged hospitalization, and some clinical complications. Total patient charges were $175,000 ($7,954 per true-positive), with no detectable clinical benefit. Our retrospective study does not support the current use of LA for rapid antigen detection. What, if any, specific indications exist for this test remain to be elucidated.

Establishing benchmarks and metrics for disruptive technologies, inappropriate and obsolete tests in the clinical laboratory

“…With the advent of vaccines to H. influenza type b and N. meningitides (A, C, Y, and W-135) the antigen testing is even less useful. The literature confirms that the use of direct antigen testing from the CSF is neither sensitive nor specific [49,50]. More importantly, the Gram stain and cultures still need to be performed regardless of the initial antigen test result.…”

“…The test's purported advantages were the rapid detection of H. influenza, N. meningitides, S. pneumoniae, and S. agalactiae. Overall, the sensitivity is essentially the same as that of a Gram-stained smear of a cyto-centrifuged CSF specimen [49,50]. With the advent of vaccines to H. influenza type b and N. meningitides (A, C, Y, and W-135) the antigen testing is even less useful.…”

Role of Molecular Diagnostics in the Management of Infectious Disease Emergencies

“…In addition, antigen in the sample can come from organism colonization of mucosal surfaces, leading to false-positive results. 8 For the immune-compromised category, a quantitative assay for Epstein-Barr virus (EBV) and cytomegalovirus (CMV) exists and is in extensive use. The quantitative assay for these pathogens and HIV are discussed in the Bloodstream and Systemic Infections section.…”

Microbiologic Investigations for Head and Neck Infections

“…An antigen-detection method is available for the presence of S pneumoniae, group B streptococcus, N meningitidis, and H influenzae type B in sterile body fluids. Most H influenzae involved in head and neck infections are non-typeable, however, and these methods reportedly are no more sensitive than an accurately performed and interpreted Gram stain, making them not very useful clinically [9]. The early diagnosis of invasive aspergillosis by the detection of circulating Aspergillus cell wall antigens (galactomannan and beta-Dglucan) has been evaluated primarily in patients who had hematologic malignancies.…”