Accuracy of urine flow cytometry and urine test strip in predicting relevant bacteriuria in different patient populations

Label-Free Analysis of Urine Samples with In-Flow Digital Holographic Microscopy

Urinary tract infections are among the most frequent infectious diseases and require screening a great amount of urine samples from patients. However, a high percentage of samples result as negative after urine culture plate tests (CPTs), demanding a simple and fast preliminary technique to screen out the negative samples. We propose a digital holographic microscopy (DHM) method to inspect fresh urine samples flowing in a glass capillary for 3 min, recording holograms at 2 frames per second. After digital reconstruction, bacteria, white and red blood cells, epithelial cells and crystals were identified and counted, and the samples were classified as negative or positive according to clinical cutoff values. Taking the CPT as reference, we processed 180 urine samples and compared the results with those of urine flow cytometry (UFC). Using standard evaluation metrics for our screening test, we found a similar performance for DHM and UFC, indicating DHM as a suitable and fast screening technique retaining several advantages. As a benefit of DHM, the technique is label-free and does not require sample preparation. Moreover, the phase and amplitude images of the cells and other particles present in urine are digitally recorded and can serve for further investigation afterwards.

Predicting urine culture results in candidates for lithotripsy

Background

Urological guidelines assert that "urine culture should be obtained" before surgical management of ureteral or kidney stones. Thus, many surgeries are delayed by 1-3 days until the results of urine culture are available. During this time, the patient frequently experience pain and possible kidney damage. We investigated the hypothesis that it is possible to predict the results of urine culture in candidates for surgical intervention using parameters that are accessible immediately upon admission.

Materials and methods

A database of 1000 patients who underwent either percutaneous nephrolithotomy (PCNL) or ureteroscopy/retrograde intrarenal surgery was analyzed. Eleven parameters potentially related to urinary infections and accessible to the clinician at the emergency department were correlated with the preoperative urine culture results.

Results

Of the patients, 234 (23.4 %) had positive cultures. On multivariate analysis, only sex, hydronephrosis grade, and history of previous nephrolithotomy were significantly associated with a positive preoperative urine culture. The risk of a positive culture can be easily determined from a simple table or an Excel-based calculator. This risk could be as low as 0.45% for a man without a history of PCNL and no hydronephrosis (4% in a woman with similar parameters) or as high as 79.5% in a man with a history of PCNL and hydronephrosis (85% in a woman with similar parameters).

Conclusions

The risk of preoperative positive urine culture can be predicted using 3 parameters that are accessible upon admission. In low-risk cases, prompt surgical treatment can be provided, eliminating the anticipation time for urine culture results.