Among clinical laboratory tests, urine testing has a particularly long history, and it continues to serve as an important screening test for kidney, urinary tract, and systemic diseases. Urine testing can accurately detect five abnormalities of urine, i.e., (1) pyuria, (2) bacteriuria, (3) hematuria, (4) proteinuria, and (5) metabolically abnormal urine (e.g., crystalluria, glycosuria). Urinary sediment examination is a morphological examination that accurately identifies and roughly counts urine formed elements, i.e., epithelial cells, blood cells, casts, salts/crystals, and bacteria, to provide information for detecting any pathological condition accompanying urine abnormalities in combination with qualitative urinary test findings. For urinary sediment examination procedures in Japan, the Japanese Committee for Clinical Laboratory Standards (JCCLS) proposed guidelines on urinary sediment examination procedures, namely GP1-P3 (urinary sediment examination procedures 2000), in 2000, and the revised version, named GP1-P4 (urinary sediment examination procedures 2010), was released in 2010. In this part, we outline the urinary sediment examination procedures according to GP1-P4 (with some modifications).
A urinary sediment examination is an important type of non-invasive, repeatable morphological examination. It is necessary to accurately classify and measure urine components, such as epithelial cells, non-epithelial cells (blood cells), casts, salts/crystals, and microorganisms. The clinical significance of a urinary sediment examination is twofold. First, this examination is used to screen for the presence of a lesion in the kidney or urinary tract; second, it is used as a means to collect information on therapeutic and adverse effects of drugs administered to treat a confirmed lesion in the kidney or urinary tract. Pathological conditions are deduced not only from the results of a urinary sediment examination but also from a comprehensive evaluation of the results from various qualitative urinary examinations, such as urinary protein and occult blood tests, as well as biochemical (blood chemical) examinations. However, advances in diagnostic imaging and immunological examinations have allowed the current use of these methods for evaluating lesions in the kidney and urinary tract, and in consequence, the value of a urinary examination used as a screening test has increased further. Given these circumstances, we wished to conduct examinations with a clear understanding of their purpose; in other words, we hope to effectively conduct urine screening examinations, consider pathological conditions based on urinary findings, and observe and provide information useful to patients and for screening participants. In this part, we will explain the role of a urinary sediment examination and also the related technical methodology.