[Detection and identification of urinary crystals using an automated urine particle analyzer coupled with a digital...

Polarized light microscopy (POM) remains the gold standard for crystalluria analysis. However, such method is time consuming and requires well-trained staff. Here, to address this issue, we tested the Sysmex UF-4000 analyzer coupled to a UD10 module as an automated flow cytometry-digital particle imaging workflow to assess (i) the ability of the system to detect and identify the crystals species and (ii) the quality of the images provided by the UD-10 module (n = 40) for each urine sample analyzed. First, systematic analysis of 76 samples by POM and the UF-4000/UD-10 analyzer showed that only attentive examination of the 40 photos was able to confidently detect crystalluria-positive samples with no misses and thus serve to discriminate positive-test crystalluria from negative-test crystalluria. These first results were confirmed by sensitivity analysis and the negative predictive value calculated on 200 samples for the results provided by the UF-4000 (39% and 46%) and after examination of the 40 UD-10 photos (100% for the both values). Digital images can therefore serve to screen crystalluria without missing crystals. A part of samples were treated by POM whereas it was not necessary (positive predictive value: 78%). Finally, we compared the crystal identification performances of the Sysmex UF4000/UD10 workflow and the ‘gold standard’ POM method on 131 urine samples containing crystals. Only calcium oxalate dihydrate crystals were identified by the Sysmex UF-4000. A close examination of the digital photographs enabled exact identification of crystals in 84.7% of the samples, suggesting however that POM is still require as soon as crystals are observed on the photographs. We conclude that a SYSMEX UF-4000 coupled with a UD-10 module can be used in practice with close examination of the photographs to discriminate positive crystalluria from negative crystalluria.