Microscopic examination of urine

Area of Science:

• Nephrology
• Urology
• Clinical Pathology

Background:

• Microscopic examination of urine sediment is crucial for diagnosing renal diseases.
• Current methods for quantifying urinary sediment components vary in reliability.
• Accurate quantification is essential for identifying subtle renal functional abnormalities.

Purpose of the Study:

• To compare the diagnostic reliability of quantitative (cells/ml) versus semi-quantitative (per high-power field, H.P.F.) urine microscopy methods.
• To assess the effectiveness of these methods in predicting renal functional abnormalities.
• To evaluate the correlation between hourly leucocyte excretion rate and quantitative leucocyte concentration.

Main Methods:

• Comparison of two urine microscopy methods: quantitative (cells/ml) and semi-quantitative (per H.P.F.), both involving centrifugation.
• Analysis of 88 duplicate urine samples from patients with suspected renal disease.
• Correlation analysis of hourly leucocyte excretion rates with quantitative leucocyte counts.

Main Results:

• The quantitative method detected abnormal urinary sediment in 74% of patients with abnormal renal function, compared to only 36% with the H.P.F. method.
• Hourly leucocyte excretion rate strongly correlated with quantitative leucocyte concentration (cells/ml), negating the need for timed urine collection.
• The H.P.F. method risks underestimating urinary abnormalities, potentially leading to misdiagnosis.

Conclusions:

• Quantitative urine microscopy (cells/ml) is significantly more reliable than the H.P.F. method for identifying renal functional abnormalities.
• Adoption of quantitative methods is necessary to prevent misclassification of abnormal urines as normal.
• Failure to use quantitative methods may lead to missed diagnoses of conditions like glomerulonephritis, falsely labeling them as 'clinically silent'.