Automated Workstation Screens Urine Before Culture

Automated systems have been developed to screen urine in order to eliminate those in which a culture is highly unlikely to yield clinically relevant results.

A flow cytometry system that quantifies urine elements associated with urinary tract infection (UTI) has recently added a new element, the detection of “all small particles” (ASP) to improve the sensitivity of the assay.

Scientists at the Veterans Affairs Medical Center (Houston, TX, USA) evaluated 1,000 urine specimens submitted consecutively that had a urine culture and urinalysis ordered on the same day. Specimens were tested for leukocyte esterase and nitrite with a chemistry dipstick analyzer and for white blood cells (WBC), ASP, bacteria, and yeast with an automated urinalysis system. Urinary samples were also tested on bacterial culture plates.

There were 893 samples from male patients, and 107 from females. There were 123 specimens from patients with indwelling urinary catheters. Of the 1,000 specimens evaluated 604 (60.4%) were culture positive at any level, that is equal to or greater than 103 colony forming units (CFU)/mL. Two combinations of results available on the iQ200 Workstation (Iris Diagnostics; Chatsworth, CA, USA) were assessed for sensitivity, specificity, and negative predictive value (NPV).One method assessed leukocyte esterase, WBCs, nitrite, and the presence of few or more bacteria or yeast, a combination chosen to reflect the current parameters combination of manual urinalysis strips and standard microscopy. The other method assessed WBCs, the presence of few or more bacteria or yeast, and an ASP count of greater than 10,000, thus eliminating the redundancy of biochemical markers and focusing on the microscopic elements available on the iQ200.

The iQ200 Workstation is used in combination with the Aution Max AX-4280 chemistry dipstick analyzer (Arkray; Edina, MN, USA). The scientists found that the dipstick analysis added no advantage in a laboratory with microscopy. Although specificities were generally low, between 65.6% and 70.1%, the goal for screening samples is high sensitivity and NPV. The NPV approached 95% in comparison to the gold standard, but was further improved to greater than 99% when compared to the ordering clinician's diagnosis or an expert review that assessed the indications in the record that a UTI was present. The authors concluded that ASP did not enhance specificity, sensitivity, or NPV. The iQ200 Workstation performed well by any standard, thus providing a reliable system by which to improve the use of laboratory resources. The study was published in the January 2013 issue of the journal Diagnostic Microbiology and Infectious Disease.

Related Links:
Veterans Affairs Medical Center
Iris Diagnostics
Arkray