Eur J Clin Microbiol Infect Dis DOI 10.1007/s10096-015-2390-1
ARTICLE
The Uni-Gold™ Streptococcus pneumoniae urinary antigen test: an interassay comparison with the BinaxNOW® Streptococcus pneumoniae test on consecutive urine samples and evaluation on patients with bacteremia S. Athlin 1 & O. Altun 2 & H. B. Eriksen 3 & V. Özenci 2 & K. Strålin 4
Received: 21 February 2015 / Accepted: 15 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The performance of the recently commercialized Uni-Gold™ Streptococcus pneumoniae test for the detection of pneumococcal antigen in urine was studied in a multicenter study. First, we studied the interassay agreement between UniGold™ and the BinaxNOW® S. pneumoniae urinary antigen test on 337 consecutive urine samples sent to the laboratory for the detection of pneumococcal antigen. The two tests performed similarly (κ=0.82): both tests positive in 27 cases, both tests negative in 299 cases, and with divergent test results in 11 cases. Secondly, the tests were run on urine samples from 203 patients with bacteremia, including 51 patients with pneumococcal bacteremia. The sensitivities and specificities were 67 and 86 % for Uni-Gold™, and 57 % and 94 % for BinaxNOW®, respectively. The false-positivity rate was significantly higher for Uni-Gold™ compared with BinaxNOW® in patients with Escherichia coli bacteremia (15 vs. 2.1 %, p=0.04), and tended to be higher in patients with bacteremia with alpha-hemolytic streptococci (32 vs. 11 %, p = 0.13). When cases with E. coli and alphahemolytic streptococci were excluded from the analysis, the overall false-positivity rate was 9/85 (11 %) for Uni-Gold™ and 6/85 (7.1 %) for BinaxNOW®. In conclusion, the study
* S. Athlin [email protected] 1
Department of Infectious Diseases, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
2
Department of Clinical Microbiology, Karolinska University Hospital Huddinge, Stockholm, Sweden
3
Department of Clinical Microbiology, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark
4
Department of Infectious Diseases, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden
showed that Uni-Gold™ was not inferior to BinaxNOW® for the detection of pneumococcal urinary antigen in patients with pneumococcal bacteremia. The specificity of UniGold™ was suboptimal due to false-positive results in cases with E. coli and alpha-hemolytic streptococci bacteremia. However, in patient populations usually subjected to testing for pneumococcal urinary antigen, such as pneumonia and meningitis patients, bacteremia with these pathogens is uncommon. The diagnostic usefulness of the Uni-Gold™ test should be further evaluated.
Introduction Streptococcus pneumoniae is a major cause of communityacquired bloodstream infection (BSI) [1]. Early and reliable establishment of pneumococcal etiology in BSI is desirable, since narrow-spectrum penicillin is the drug of choice for pneumococcal infections in most parts of the world [2]. Rapid evidence of pneumococcal etiology in adult patients with BSI may be yielded by the detection of pneumococcal antigen in urine, even after antibiotic treatment has been initiated [3]. Since 1999, the BinaxNOW® S. pneumoniae test (Alere, USA) has been available for routine use on urine samples [4]. This test detects soluble antigens common for all pneumococcal serotypes, the pneumococcal cell-wall polysaccharides [5]. In a recent meta-analysis of 27 studies, the pooled sensitivity of the BinaxNOW® test was estimated to be 74.0 % and the specificity to be 97.2 % for the diagnosis of pneumococcal etiology in adult hospitalized patients with pneumonia [6]. In patients with pneumococcal BSI, studies have reported sensitivities from 70 to 100 %, dependent on the sample size and study design [4]. Previously, we have shown that the BinaxNOW® test is clinically useful for narrowing antibiotic treatment to β-lactam monotherapy [7].
Eur J Clin Microbiol Infect Dis
Since 2013, a new rapid urinary antigen test has been commercially available, the Uni-Gold™ S. pneumoniae test (Trinity Biotech, USA). The test is a lateral flow immunoassay for the qualitative detection of pneumococcal soluble antigens in human urine and cerebral spinal fluid, developed by Statens Serum Institut Diagnostica, Denmark, in cooperation with Trinity Biotech. As for the BinaxNOW® test, the Uni-Gold™ test provides a result within 15 min and is intended, in conjunction with culture and other methods, as an aid in the diagnosis of serious pneumococcal infections. Performance studies by the manufacturer demonstrate a sensitivity of 87.7 % on urine from patients with retrospectively collected blood cultures positive for S. pneumoniae and a specificity of 92.4 % on urine samples from blood culturenegative patients (package leaflet). These results have not yet been reproduced by any independent research group or applied to a clinical setting. In the present study, we aimed to study the performance of the Uni-Gold™ test. First, we studied the interassay agreement between the Uni-Gold™ and the BinaxNOW® tests on consecutive clinical urine samples. Secondly, we studied the performance on urine samples from patients with pneumococcal and non-pneumococcal bacteremia.
Performance in bacteremic patients
Materials and methods
Urinary antigen tests
Study design
The Uni-Gold™ and BinaxNOW® tests were performed on non-concentrated urine according to the manufacturers’ instructions. All urine samples were tested consecutively after collection and stored at 6 °C no longer than 14 days before testing. No clinical or microbiological data from the patients were known when testing for the interassay agreement of the two tests. According to the manufacturer, the Uni-Gold™ test is a lateral flow immunoassay with several parts overlapping one another and mounted on a backing card to form the test strip. Before running the test, three drops of urine and two drops of extraction buffer are mixed in a test tube. As the test strip is inserted into the test tube, the urine/extraction buffer sample is absorbed into the sample pad of the test strip. The sample migrates upwards through the sample pad to a conjugate pad, where colored latex particles, conjugated with rabbit anti-S. pneumoniae antibodies, are dried onto inert glass fiber. As the sample passes over the conjugate pad, any S. pneumoniae antigen in the sample combines with the conjugate to form an antigen–conjugate complex. The complex migrates upwards to a nitrocellulose membrane, where it binds to rabbit anti-S. pneumoniae antibodies coated on a test line region, forming a visible pink/red line. Excess conjugate binds to goat anti-rabbit antibodies coated on the control line region, forming a second pink/red line. A permanent blue line
The Uni-Gold™ test was evaluated in a multicenter study at three tertiary university hospitals: Örebro University Hospital (550 beds), Örebro, Sweden; Karolinska University Hospital Huddinge (800 beds), Stockholm, Sweden; and Copenhagen University Hospital Hvidovre (800 beds), Copenhagen, Denmark. All tested samples were identified in the laboratory after collection in routine practice. When the Uni-Gold™ and BinaxNOW® tests had been performed, and age, gender, and results from routine cultures had been added to the test results, all data were anonymized.
Interassay agreement Between 22th July and 20th November 2013, we prospectively studied the interassay agreement between the Uni-Gold™ and BinaxNOW® tests. All consecutive urine samples, which were sent to the laboratory for testing with the BinaxNOW® test, were also tested with the Uni-Gold™ test. In cases with only one of the two tests positive, we determined if any routine culture, collected within 2 days before the collection of urine, was positive for S. pneumoniae.
Between 8th August 2013 and 31st March 2014, the UniGold™ and BinaxNOW® tests were performed on urine samples, collected in routine practice for culture or antigen detection, from patients with bacteremia. Cases with coagulasenegative staphylococci detected in one blood culture bottle were not included. Only urine samples collected within 2 days from the collection of the positive blood culture were included. In cases with non-pneumococcal bacteremia with a positive urinary antigen test, we determined if any routine culture, collected within 2 days before the collection of urine, was positive for S. pneumoniae. The results from urine cultures were recorded. Routine microbiological tests For blood culturing, a BACTEC™ (Becton, Dickinson and Company, USA) blood culturing system was used at Örebro University Hospital, and a BacT/ALERT® (bioMérieux, USA) blood culturing system was used at Karolinska University Hospital Huddinge and Copenhagen University Hospital Hvidovre. Cultures on respiratory secretions and species identification were performed with accredited routine laboratory methods.
Eur J Clin Microbiol Infect Dis
is printed on the membrane cover between the test line and the control line regions. The test result is read visually at 15 min only. The test result is valid only if the control line appears as a visible pink/red line in the control region. Two pink/red colored lines of any intensity located above and below the central blue printed line indicate a positive result, while a single pink/ red control line of any intensity above the central blue line indicates a negative result. The principles and procedures of the BinaxNOW® test have been described previously [8]. Statistics The interassay agreement between the tests was estimated by calculating Cohan’s unweighted kappa coefficient (κ). McNemar’s test was used for the comparison of sensitivity and specificity rates. A confidence interval (CI) of 95 % was used for statistical precision. A two-tailed p-value of
ARTICLE
The Uni-Gold™ Streptococcus pneumoniae urinary antigen test: an interassay comparison with the BinaxNOW® Streptococcus pneumoniae test on consecutive urine samples and evaluation on patients with bacteremia S. Athlin 1 & O. Altun 2 & H. B. Eriksen 3 & V. Özenci 2 & K. Strålin 4
Received: 21 February 2015 / Accepted: 15 April 2015 # Springer-Verlag Berlin Heidelberg 2015
Abstract The performance of the recently commercialized Uni-Gold™ Streptococcus pneumoniae test for the detection of pneumococcal antigen in urine was studied in a multicenter study. First, we studied the interassay agreement between UniGold™ and the BinaxNOW® S. pneumoniae urinary antigen test on 337 consecutive urine samples sent to the laboratory for the detection of pneumococcal antigen. The two tests performed similarly (κ=0.82): both tests positive in 27 cases, both tests negative in 299 cases, and with divergent test results in 11 cases. Secondly, the tests were run on urine samples from 203 patients with bacteremia, including 51 patients with pneumococcal bacteremia. The sensitivities and specificities were 67 and 86 % for Uni-Gold™, and 57 % and 94 % for BinaxNOW®, respectively. The false-positivity rate was significantly higher for Uni-Gold™ compared with BinaxNOW® in patients with Escherichia coli bacteremia (15 vs. 2.1 %, p=0.04), and tended to be higher in patients with bacteremia with alpha-hemolytic streptococci (32 vs. 11 %, p = 0.13). When cases with E. coli and alphahemolytic streptococci were excluded from the analysis, the overall false-positivity rate was 9/85 (11 %) for Uni-Gold™ and 6/85 (7.1 %) for BinaxNOW®. In conclusion, the study
* S. Athlin [email protected] 1
Department of Infectious Diseases, Faculty of Medicine and Health, Örebro University, Örebro, Sweden
2
Department of Clinical Microbiology, Karolinska University Hospital Huddinge, Stockholm, Sweden
3
Department of Clinical Microbiology, Copenhagen University Hospital Hvidovre, Copenhagen, Denmark
4
Department of Infectious Diseases, Karolinska Institutet, Karolinska University Hospital Huddinge, Stockholm, Sweden
showed that Uni-Gold™ was not inferior to BinaxNOW® for the detection of pneumococcal urinary antigen in patients with pneumococcal bacteremia. The specificity of UniGold™ was suboptimal due to false-positive results in cases with E. coli and alpha-hemolytic streptococci bacteremia. However, in patient populations usually subjected to testing for pneumococcal urinary antigen, such as pneumonia and meningitis patients, bacteremia with these pathogens is uncommon. The diagnostic usefulness of the Uni-Gold™ test should be further evaluated.
Introduction Streptococcus pneumoniae is a major cause of communityacquired bloodstream infection (BSI) [1]. Early and reliable establishment of pneumococcal etiology in BSI is desirable, since narrow-spectrum penicillin is the drug of choice for pneumococcal infections in most parts of the world [2]. Rapid evidence of pneumococcal etiology in adult patients with BSI may be yielded by the detection of pneumococcal antigen in urine, even after antibiotic treatment has been initiated [3]. Since 1999, the BinaxNOW® S. pneumoniae test (Alere, USA) has been available for routine use on urine samples [4]. This test detects soluble antigens common for all pneumococcal serotypes, the pneumococcal cell-wall polysaccharides [5]. In a recent meta-analysis of 27 studies, the pooled sensitivity of the BinaxNOW® test was estimated to be 74.0 % and the specificity to be 97.2 % for the diagnosis of pneumococcal etiology in adult hospitalized patients with pneumonia [6]. In patients with pneumococcal BSI, studies have reported sensitivities from 70 to 100 %, dependent on the sample size and study design [4]. Previously, we have shown that the BinaxNOW® test is clinically useful for narrowing antibiotic treatment to β-lactam monotherapy [7].
Eur J Clin Microbiol Infect Dis
Since 2013, a new rapid urinary antigen test has been commercially available, the Uni-Gold™ S. pneumoniae test (Trinity Biotech, USA). The test is a lateral flow immunoassay for the qualitative detection of pneumococcal soluble antigens in human urine and cerebral spinal fluid, developed by Statens Serum Institut Diagnostica, Denmark, in cooperation with Trinity Biotech. As for the BinaxNOW® test, the Uni-Gold™ test provides a result within 15 min and is intended, in conjunction with culture and other methods, as an aid in the diagnosis of serious pneumococcal infections. Performance studies by the manufacturer demonstrate a sensitivity of 87.7 % on urine from patients with retrospectively collected blood cultures positive for S. pneumoniae and a specificity of 92.4 % on urine samples from blood culturenegative patients (package leaflet). These results have not yet been reproduced by any independent research group or applied to a clinical setting. In the present study, we aimed to study the performance of the Uni-Gold™ test. First, we studied the interassay agreement between the Uni-Gold™ and the BinaxNOW® tests on consecutive clinical urine samples. Secondly, we studied the performance on urine samples from patients with pneumococcal and non-pneumococcal bacteremia.
Performance in bacteremic patients
Materials and methods
Urinary antigen tests
Study design
The Uni-Gold™ and BinaxNOW® tests were performed on non-concentrated urine according to the manufacturers’ instructions. All urine samples were tested consecutively after collection and stored at 6 °C no longer than 14 days before testing. No clinical or microbiological data from the patients were known when testing for the interassay agreement of the two tests. According to the manufacturer, the Uni-Gold™ test is a lateral flow immunoassay with several parts overlapping one another and mounted on a backing card to form the test strip. Before running the test, three drops of urine and two drops of extraction buffer are mixed in a test tube. As the test strip is inserted into the test tube, the urine/extraction buffer sample is absorbed into the sample pad of the test strip. The sample migrates upwards through the sample pad to a conjugate pad, where colored latex particles, conjugated with rabbit anti-S. pneumoniae antibodies, are dried onto inert glass fiber. As the sample passes over the conjugate pad, any S. pneumoniae antigen in the sample combines with the conjugate to form an antigen–conjugate complex. The complex migrates upwards to a nitrocellulose membrane, where it binds to rabbit anti-S. pneumoniae antibodies coated on a test line region, forming a visible pink/red line. Excess conjugate binds to goat anti-rabbit antibodies coated on the control line region, forming a second pink/red line. A permanent blue line
The Uni-Gold™ test was evaluated in a multicenter study at three tertiary university hospitals: Örebro University Hospital (550 beds), Örebro, Sweden; Karolinska University Hospital Huddinge (800 beds), Stockholm, Sweden; and Copenhagen University Hospital Hvidovre (800 beds), Copenhagen, Denmark. All tested samples were identified in the laboratory after collection in routine practice. When the Uni-Gold™ and BinaxNOW® tests had been performed, and age, gender, and results from routine cultures had been added to the test results, all data were anonymized.
Interassay agreement Between 22th July and 20th November 2013, we prospectively studied the interassay agreement between the Uni-Gold™ and BinaxNOW® tests. All consecutive urine samples, which were sent to the laboratory for testing with the BinaxNOW® test, were also tested with the Uni-Gold™ test. In cases with only one of the two tests positive, we determined if any routine culture, collected within 2 days before the collection of urine, was positive for S. pneumoniae.
Between 8th August 2013 and 31st March 2014, the UniGold™ and BinaxNOW® tests were performed on urine samples, collected in routine practice for culture or antigen detection, from patients with bacteremia. Cases with coagulasenegative staphylococci detected in one blood culture bottle were not included. Only urine samples collected within 2 days from the collection of the positive blood culture were included. In cases with non-pneumococcal bacteremia with a positive urinary antigen test, we determined if any routine culture, collected within 2 days before the collection of urine, was positive for S. pneumoniae. The results from urine cultures were recorded. Routine microbiological tests For blood culturing, a BACTEC™ (Becton, Dickinson and Company, USA) blood culturing system was used at Örebro University Hospital, and a BacT/ALERT® (bioMérieux, USA) blood culturing system was used at Karolinska University Hospital Huddinge and Copenhagen University Hospital Hvidovre. Cultures on respiratory secretions and species identification were performed with accredited routine laboratory methods.
Eur J Clin Microbiol Infect Dis
is printed on the membrane cover between the test line and the control line regions. The test result is read visually at 15 min only. The test result is valid only if the control line appears as a visible pink/red line in the control region. Two pink/red colored lines of any intensity located above and below the central blue printed line indicate a positive result, while a single pink/ red control line of any intensity above the central blue line indicates a negative result. The principles and procedures of the BinaxNOW® test have been described previously [8]. Statistics The interassay agreement between the tests was estimated by calculating Cohan’s unweighted kappa coefficient (κ). McNemar’s test was used for the comparison of sensitivity and specificity rates. A confidence interval (CI) of 95 % was used for statistical precision. A two-tailed p-value of
