Urine analysis – Evolution and trends in automation

Around 6000 years ago, laboratory medicine began with the analysis of human urine, referred to as uroscopy, later termed as urinalysis. The word uroscopy derives from two Greek words: ouron, which means urine and skopeoa, which means to behold, contemplate, examine, and inspect.

By the late 12th century, Gilles de Corbeil, a French scholar classified 20 different types of urine, recording differences in urine sediment and color. In 1630, Nicolas Fabricius de Peiresc, a French astronomer and naturalist, did the first microscopic description of urine crystals as a heap of rhomboidal bricks. These few examples illustrate the development of urinalysis, which continues to be a formidable and cost-effective tool to obtain crucial information for diagnostic purposes.

A complete urinalysis consists of three components – physical, chemical, and microscopy. Physical examination describes the volume, color, clarity, odor, and specific gravity. Chemical examination identifies pH, red blood cells, white blood cells, proteins, glucose, urobilinogen, bilirubin, ketone bodies, leukocyte esterase, and nitrites. Microscopic examination encompasses the detection of casts, cells, crystals, and microorganisms.

Accurate collection, storage, and handling are crucial to maintaining the sample’s integrity. Morning urine is considered as the best representative for testing. The urine accumulated overnight in the bladder is more concentrated and provides an insight into the kidneys’ concentrating capacity and allows for the detection of trace amounts of substances that may not be present in more diluted samples. However, other types of urine specimens may be ordered according to specific purposes (randomly, 2-hours postprandial, 24-hour collection, etc.).

Furthermore, urine should be ideally examined within the first hour after the collection due to the instability of some urinary components (cells, casts, and crystals). If not possible, the sample should be kept at 4°C for up to 24 hours, which will slow down the decomposition process. Any specimen older than 24 hours should not be used for urinalysis.

The limitation of manual visualization of urine strips made way for automation, and we were able to see a paradigm shift in the laboratory operations recently. Small, medium-sized, and chain laboratories have started moving towards automation by using urine strips for biochemical analysis.

A few manufacturers provide urine strips from 2 to 14 parameters, suiting a particular laboratory’s requirement. The semi-quantitative and quantitative reading of urine strips, using reflectance photometry, has made it possible to get reliable and accurate results.

The introduction of CMOS (complementary metal oxide semiconductor) technology has enhanced analytical sensitivity and shown promise in microalbuminuria testing.

Urine flow cytometry is an advanced alternative technology for automated microscopy, enabling rapid differentiation of urinary cells and formed elements with many value-added information and flags.

An interesting recent evolution is the use of smart phones for reading and interpreting urine strip results, based on the reflectance theory. The greater emphasis on chronic kidney disease and diabetic nephropathy has fuelled a high demand for urinalysis.

The advancement in technologies used for the automation of urine analysis has proved to be a boon for clinicians for monitoring the diagnosis of diseases.