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Urinalysis Continued

The Microscopic Exam

Microscopic Exam Background

Introduction

A microscopic examination is a procedure to determine if cells, crystals, casts, and microorganisms are present in the urine. If performed manually, the examination begins by placing about 10 milliliters of urine in a glass tube, then centrifuging the contents for about 5 minutes. A small portion of the sediment is placed on a glass slide and flattened with a coverslip. The glass slide is then moved to a microscope stage and surveyed for suspended components.

Cells Found in Urine

Squamous epithelial cells – line the distal end of the urethra and cover the inner surface of the vagina. A high number (> 20 per High-Power Field; 400X) indicates the sample may be contaminated.

Renal tubular epithelial cells (RTEs) originate from the walls of the nephron tubules in the kidney, including the distal and proximal convoluted tubules and collecting ducts. Two or more cells per HPF indicate damage to the renal tubules. 

Transitional epithelial cells line the interior of the ureters, bladder, and a portion of the urethra. More than a few cells per HPF indicates a possible urinary tract infection (UTI).

Red blood cells in high numbers (> 5 five per HPF) indicate bleeding along the urinary tract or prostate. Possible causes for urinary tract bleeding are kidney infection or disease, urinary tract infections (UTIs), kidney or bladder stones, and kidney injury.

White blood cells (most commonly neutrophils) above 5 cells per HPF indicate a possible bacterial urinary tract infection (UTI) or inflammation of the urinary tract or kidneys.

Crystals Found in Urine

Crystals appear in the urine when particular substances become too concentrated, and they aggregate to form larger solids, often due to dehydration. Dehydration, the overconsumption of certain foods, changes in urine pH, or certain medicines can cause crystals to form.

The accumulation of crystals can cause stones that block the urinary tract passageways (kidney stones), urinary tract infections (UTIs), and kidney infections.

Substances that often combine to form crystals include calcium oxalate, uric acid, struvite (triple phosphate crystals), cystine, bilirubin, and calcium carbonate.

Urine Crystals that are Often Present in Small Numbers

Urine Crystals that Indicate Pathology and Should Not be Present

Casts Found in Urine

Casts are relatively large cylindrical structures, each having a matrix made of glycoproteins (Tamm-Horsfall proteins). The epithelial cells of the nephron tubules secrete the matrix glycoproteins, especially if the urine pH is low, urine concentration is high, or the urine flow rate is low. Because of their large size, casts are typically viewed at 100X. 

The most common type of cast, the hyaline cast, consists primarily of matrix glycoproteins. They often appear in the urine in low numbers due to stress, dehydration, or strenuous exercise and are usually not concerning.

In comparison, casts containing erythrocytes, leukocytes, epithelial cells, or fat indicate kidney disease or infection and should not be present in the urine. Granular and waxy casts probably result from the degeneration of cellular casts, and are also associated with kidney disease or infection.

Microorganisms Found in Urine

Microorganisms are usually not in the urine. Their presence, even in lows numbers, indicates a bacterial, fungal, or parasitic infection of the urinary tract (kidney, ureters, bladder, and urethra).

Microscopic Exam Procedures

Microscopic Exam Results

Urine Sediment Identification Images

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References /Attributions

General

The University of Utah – Urinalysis

Cells

Labpedia – Urine Analysis:- Microscopic Examination, and Interpretations

Oxford University Press – Cells in the Urine Sediment

National Library of Medicine (NIH) – Urinalysis

The University of Wisconsin School of Pharmacy – Urinalysis Interpretation

Crystals

Illinois State Veterinary Medical Association – Urinalysis Made Easy

Kidney Support and Protection – Can You Prevent Kidney Stones

Medical News Today – Urine Crystals

National Kidney Foundation – Kidney Stones

NIH National Library of Medicine – Urinary pH and Stone Formation

Casts

Cornell University College of Veterinary Medicine – Casts

Lincoln Memorial University – Urinalysis

Oxford University Press – Casts in the Urine Sediment

Renal Fellow – Granular and “Muddy Brown” Casts

Renak Fellow – Waxy Casts

University of California (San Francisco) – Urinary Casts

Microorganisms

Clevand Clinic – Urinary Tract Infections