Description

The PA-100-AST urine analyzer from Sysmex is a rapid point-of-care test currently registered as a medicinal product. The system identifies bacteriuria (≥ 50,000 CFU/mL) and reports antibiotic susceptibility results as susceptible (S), susceptible with increased exposure (I), resistant (R), or not applicable (NA) for amoxicillin/clavulanic acid, ciprofloxacin, fosfomycin, nitrofurantoin, and trimethoprim, based on EUCAST standards. Although the system detects bacteriuria, it does not inform the user of the specific bacterial species involved, providing only a positive or negative result.

The PA-100 cartridge is designed to detect common uropathogens: Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, and Staphylococcus saprophyticus. A proprietary internal algorithm classifies bacteria into one of three groups (Enterobacterales, Staphylococcus, or Enterococcus) and applies appropriate EUCAST breakpoints.

This product is authorized and CE-marked in the European Union for point-of-care use in women with suspected uncomplicated urinary tract infections (UTIs).

However, the PA-100-AST system has not yet been evaluated in a general practice setting. The goal of this study is to compare the results of the Sysmex PA-100-AST with laboratory-based urine culture in a consecutive sample of adult women recruited from general practices.

Recruitment. Adult, non-pregnant women with symptoms suggestive of uncomplicated UTI will be recruited consecutively and prospectively during routine consultations in at least four general practices across two German practice-based research networks (Bavaria and Thuringia). Informed consent will be obtained from all participants.

Outcomes. The primary outcome measure is diagnostic accuracy compared with urine culture. Urine culture positivity is defined as a bacterial count of at least 50,000 CFU/ml (per the instructions for use) of one of the species detected by the PA-100-AST (index test). Additionally, the diagnostic accuracy of the index test will be assessed against varying thresholds for urine culture positivity (from 1,000 to 100,000 CFU/ml or greater).

Another key outcome is the agreement between the susceptibility test results from the index test and the reference laboratory-based susceptibility test. Exploratory subgroup analyses will include assessments based on age, dipstick test results, and symptom severity at presentation.

Data Collection. The index test will be conducted immediately after enrolment on fresh urine (within 30 minutes of collection). A pragmatic approach will be followed, with microbiological analysis carried out by the laboratories that typically serve the participating practices. These laboratories adhere to common quality standards according to the German laboratory guidelines (Harnwegsinfektionen: Qualitätsstandards in der mikrobiologisch-infektiologischen Diagnostik, MIQ-02) and apply EUCAST criteria for susceptibility testing. According to STARD recommendations, clinicians performing the index test, as well as laboratory technicians and microbiologists conducting the urine culture, are blinded to the results of each other´s tests. Clinical data are collected using a validated patient questionnaire at the initial presentation, and management decisions are recorded during routine consultation. Dipstick test results are measured through Combur test stripes (Roche Diagnostics).

Data Analysis. Descriptive statistics will be presented using appropriate summary measures such as mean (SD), median (IQR), and absolute and relative frequencies.

Diagnostic accuracy measures (sensitivity, specificity, predictive values, and likelihood ratios) will be reported with corresponding 95% confidence intervals.

Kappa coefficients and corresponding statistical tests will be used to assess agreement between categorical variables (with statistical significance set at p less than 0.05) for susceptibility test results.

Sample Size. The initial sample size calculation assumed a sensitivity of 98.8% and specificity of 98.4% based on manufacturer data. Given a prevalence of 70%, we estimated that 101 patients would be required to estimate specificity, and 51 patients to estimate sensitivity, with a 95% confidence interval (CI) width of 0.1. However, after the protocol was approved, a clinical evaluation in a hospital setting (PMID: 38825624) was published, reporting a sensitivity of 84% and a specificity of 99.4% for the PA-100-AST, using a threshold of 50,000 CFU/ml as per the instructions for use. Given the more realistic estimates from this study, the sample size was recalculated. Based on the revised sensitivity and specificity estimates, and a 50,000 CFU/ml culture positivity threshold for which a decreased prevalence from 0.70 to 0.60 can be expected, the required sample size increased from 101 to 345 participants. Due to no project-specific funding, and in agreement with the sponsor, this was deemed unfeasible. Therefore, the aim to recruit 200 participants, which, under the assumption outlined above, will result in a 95%CI width of 0.13 instead of the initially planned width of 0.1.

Role of manufacturer. This study is investigator-initiated. Sysmex has provided the urine analyzer free of charge but has no involvement in the study design, implementation (aside from supplying detailed instructions for use as well as technical assistance), data preparation, analysis, interpretation, or publication of results. None of the investigators receive any funding or benefits from Sysmex or other device manufacturers.