Evaluation of BD Vacutainer Plus Urine C&S Preservative Tubes
Evaluation of BD Vacutainer Plus Urine C&S Preservative Tubes
Objectives: The stability of urine specimens submitted for culture remains a challenge for many laboratories because of delays in specimen transport. We evaluated the usefulness of BD Vacutainer Plus Urine C&S Preservative Tube in ensuring specimen stability.
Methods: Clinical urine specimens collected in sterile collection cups (n = 110) were plated onto sheep blood and MacConkey agar following standard laboratory procedures guidelines. Thereafter, specimens were divided into 3 storage conditions: nonpreservative, refrigerated; nonpreservative, room temperature (RT); BD Vacutainer Plus Urine C&S Preservative Tube, RT. For each sample type, additional cultures were set up at 2, 4, 24, and 48 hours.
Results: Initially, 18 specimens had no growth, 32 showed mixed skin flora, and 60 yielded at least 1 uropathogen. Increased colony counts of uropathogens were observed for nonpreserved urine samples stored at RT; these changes were statistically significant. Minor differences between refrigerated urine samples and BD Vacutainer Plus Urine C&S Preservative Tube samples were seen but were not statistically significant.
Conclusions: The use of preservative-containing collection tubes is desirable to ensure specimen stability when prompt processing or refrigeration is not feasible.
Urinary tract infections (UTIs) are among the most commonly encountered infectious diseases, and urine specimens submitted for quantitative bacterial culture account for a significantly large volume of test requests in clinical microbiology laboratories. The gold standard for diagnosis of a UTI is the detection of a urinary pathogen via culture in freshly collected urine specimens. Typically, patients are asked to provide a "clean-catch," midstream urine specimen. Other specimen types may include those obtained from a catheter (single, straight catheter, or Foley catheter) or from a suprapubic aspiration of the bladder. Considering the human anatomy of the urinary tract, it is not surprising that UTIs are among the most common bacterial infections. However, voided urine samples are frequently contaminated by organisms of the urethral, skin, genital, and/or fecal flora. The importance of appropriate specimen collection and transport to avoid contamination has been previously described. Usually, contaminant organisms are present in low numbers, ie, less than 10 colony-forming units (CFU)/mL, whereas uropathogens are present in significantly higher numbers, usually greater than 10 CFU/mL. However, over time, even contaminant microorganisms can grow to significantly high numbers when specimens are left at room temperature (>15°C). The effects of delayed urine culture as well as impact of various transport and storage conditions have been described.
The current guidelines for urine collection, transport, and culture emphasize the need for using either transport tubes containing preservatives or the need for not exceeding the 2-hour interval from collection to processing. If preservative tubes are not used and a transport time of less than 2 hours may not be achievable, refrigeration of the urine specimen has been shown to also limit the overgrowth of organisms; however, it is unrealistic to expect that no urine specimen will spend more than 2 cumulative hours unrefrigerated in most settings. In the 2005 College of American Pathologists (CAP) Q-Probes study on urine culture contamination, the investigators found that only a small number of microbiology laboratories enforce the 2-hour cutoff rule for limiting transport time of urine specimens. Because most of the evidence on specimen integrity for urine is based on studies performed in the 1980s, and considering that in the CAP Q-Probes study most laboratory sites used refrigeration of urine specimen for preservation, we decided to investigate the usefulness of the BD Vacutainer Plus Urine C&S Preservative Tube (BDU; Becton Dickinson, Franklin Lakes, NJ) and compare its performance to refrigerated nonpreservative and room-temperature–exposed nonpreservative urine specimens. This study further aimed at assessing stability of both the specimen and CFU counts over time.
Abstract and Introduction
Abstract
Objectives: The stability of urine specimens submitted for culture remains a challenge for many laboratories because of delays in specimen transport. We evaluated the usefulness of BD Vacutainer Plus Urine C&S Preservative Tube in ensuring specimen stability.
Methods: Clinical urine specimens collected in sterile collection cups (n = 110) were plated onto sheep blood and MacConkey agar following standard laboratory procedures guidelines. Thereafter, specimens were divided into 3 storage conditions: nonpreservative, refrigerated; nonpreservative, room temperature (RT); BD Vacutainer Plus Urine C&S Preservative Tube, RT. For each sample type, additional cultures were set up at 2, 4, 24, and 48 hours.
Results: Initially, 18 specimens had no growth, 32 showed mixed skin flora, and 60 yielded at least 1 uropathogen. Increased colony counts of uropathogens were observed for nonpreserved urine samples stored at RT; these changes were statistically significant. Minor differences between refrigerated urine samples and BD Vacutainer Plus Urine C&S Preservative Tube samples were seen but were not statistically significant.
Conclusions: The use of preservative-containing collection tubes is desirable to ensure specimen stability when prompt processing or refrigeration is not feasible.
Introduction
Urinary tract infections (UTIs) are among the most commonly encountered infectious diseases, and urine specimens submitted for quantitative bacterial culture account for a significantly large volume of test requests in clinical microbiology laboratories. The gold standard for diagnosis of a UTI is the detection of a urinary pathogen via culture in freshly collected urine specimens. Typically, patients are asked to provide a "clean-catch," midstream urine specimen. Other specimen types may include those obtained from a catheter (single, straight catheter, or Foley catheter) or from a suprapubic aspiration of the bladder. Considering the human anatomy of the urinary tract, it is not surprising that UTIs are among the most common bacterial infections. However, voided urine samples are frequently contaminated by organisms of the urethral, skin, genital, and/or fecal flora. The importance of appropriate specimen collection and transport to avoid contamination has been previously described. Usually, contaminant organisms are present in low numbers, ie, less than 10 colony-forming units (CFU)/mL, whereas uropathogens are present in significantly higher numbers, usually greater than 10 CFU/mL. However, over time, even contaminant microorganisms can grow to significantly high numbers when specimens are left at room temperature (>15°C). The effects of delayed urine culture as well as impact of various transport and storage conditions have been described.
The current guidelines for urine collection, transport, and culture emphasize the need for using either transport tubes containing preservatives or the need for not exceeding the 2-hour interval from collection to processing. If preservative tubes are not used and a transport time of less than 2 hours may not be achievable, refrigeration of the urine specimen has been shown to also limit the overgrowth of organisms; however, it is unrealistic to expect that no urine specimen will spend more than 2 cumulative hours unrefrigerated in most settings. In the 2005 College of American Pathologists (CAP) Q-Probes study on urine culture contamination, the investigators found that only a small number of microbiology laboratories enforce the 2-hour cutoff rule for limiting transport time of urine specimens. Because most of the evidence on specimen integrity for urine is based on studies performed in the 1980s, and considering that in the CAP Q-Probes study most laboratory sites used refrigeration of urine specimen for preservation, we decided to investigate the usefulness of the BD Vacutainer Plus Urine C&S Preservative Tube (BDU; Becton Dickinson, Franklin Lakes, NJ) and compare its performance to refrigerated nonpreservative and room-temperature–exposed nonpreservative urine specimens. This study further aimed at assessing stability of both the specimen and CFU counts over time.
Source...