Microscopic examination of urine sediment: Phase contrast versus bright field

Today, phase contrast microscopy (PCM) is the recommended technique for manual urinary sediment (U-sed) examination. In fact, compared to bright field microscopy (BFM), it allows a better identification of most U-sed particles.

The main contributions, both as original papers in medical journals and as monographs on PCM applied to U-sed examination, published in the period 1950-1982 (which was chosen because it includes the results of the most important investigations on the subject) were identified and analysed. Moreover, a brief analysis on the use of PCM in U-sed examination today was carried out.

After the discovery of PCM by the Dutch physicist Frits Zernike in the 1930s, several contributions were published, most of which are forgotten today. All of them demonstrated the advantages of PCM over BFM in identifying the U-sed particles, especially casts, renal tubular epithelial cells, atypical urothelial cells associated with urothelial carcinoma, and erythrocytes (which for the 1st time were classified as dysmorphic - of glomerular origin - and isomorphic - of non glomerular origin). The analysis of six recent monographs on U-sed or urinalysis, written in English and with an international distribution, demonstrated that only in two of them the U-sed particles were mostly shown by PCM.

Several papers and monographs, published since the early 1950s, have demonstrated the advantages of PCM over BFM for U-sed examination. In spite of this, PCM is not as widely used as it should be.