A sample of fresh urine is dropped onto a plate for immediate analysis under a microscope. White blood cells and epithelial cells are counted as markers of an infection. When infection occurs in the urinary tract, the immune system tries to remove infected cells by shedding the cells in the bladder lining (the epithelium) to be excreted during urination – these are known as epithelial cells.

A high white blood cell count usually indicates that the body is fighting an infection. White blood cells rush in to help destroy the harmful substance and prevent the infection developing further.

White blood cells degrade very quickly. Studies have shown this occurs in as little as four hours unless stored in the correct conditions so a sample sent for analysis at the laboratory will not pick them up.

Professor James Malone-Lee, Emeritus Professor of Nephrology, UCL notes in two published studies: “Analysis of urothelial and clue cells is novel, as is sediment culture, but these methods have been well validated and have a strong pathophysiological foundation. Fresh urine microscopy is not commonly adopted in clinical practice nowadays, nevertheless, it has been well validated in studies dating back to 1928 and is still unsurpassed as a surrogate marker of infection”. (1)

“Pyuria, detected by microscopy of a fresh midstream urine (MSU) specimen, is the most sensitive surrogate marker of UTI. It circumvents the problems associated with quantitative (numerical) bacterial culture, and its value in the diagnosis of UTI is recognised by international practice guidelines. Whilst ≥10 wbc in a micro litre of urine is employed almost universally to diagnose UTI, contemporary data cast doubt on this threshold in patients with LUTS. In the symptomatic patient, controlled studies have demonstrated that lower pyuria counts of 1–9 wbc in a micro litre of urine are associated with an increase in independent inflammatory and microbiological markers of UTI. Thus, lower levels of pyuria may also indicate infection and immune activation”.(2)

Issues with urine microscopy

• Urine samples must be fresh, that is within two hours of urination to prevent degradation of the white blood cells otherwise the sample must be discarded
• Training of staff to interpret samples via microscopy plus the cost of the relevant microscope
• Acceptance by clinicians of the results and then appropriate treatment prescription. At present urine testing is biased towards bacterial identification. Urine microscopy, once the standard for urine analysis, was superseded by the automated methods introduced since the 1960s preferred for their time-saving benefits.

References:

1. A blinded observational cohort study of the microbiological ecology associated with pyuria and overactive bladder symptoms. Kiren Gill, Ryoon Kang, Sanchutha Sathiananthamoorthy, Rajvinder Khasriya, James Malone-Lee. International Urogynecology Journal, January 2018