Urine Analysis and Formation

Urine Analysis

• Urine analysis is the physical, chemical, and microscopic examination of urine, providing information on a patient's general health, clinical picture, and potential diseases.

Urine Formation

• Urine is formed in the kidney and excreted by the urinary system.
• Urine formation occurs in the nephron, the functional unit of the kidney, through a process of filtration, reabsorption, and secretion.
• The nephron consists of a blood vessel called the glomerulus, where blood is filtered into Bowman's capsule.
• The filtration process is known as glomerular filtrate, and approximately 180L of glomerular filtrate is produced daily, with only 1-2L of urine eliminated from the normal body.
• Urinary pH is determined in the distal convoluted tubule, where hydrogen and ammonium ions may be excreted in exchange for sodium.

Urine Composition

• Urine composition depends on factors such as diet, nutritional status, metabolic rate, general state of the body, and kidney function.
• Urine is composed of 96% water and 4% dissolved substances, including salt, urea, and other inorganic substances like K, Ca, Mg, NH3, and PO4.
• Abnormal constituents in urine may include RBC, WBC, fat, glucose, casts, bile, acetone, and hemoglobin.

Urine Specimen Collection

• Types of urine specimens include random, 24-hour, clean catch/midstream, first morning specimen, catheter, and suprapubic aspiration.
• The first morning specimen is preferred, being the most concentrated and representative of the 24-hour urine output.
• Catheterized urine specimens are collected when indicated, but are invasive and may cause discomfort and increased risk of urinary infection.

Specimen Collection and Storage

• Urine specimens should be collected in a dry, clean container, with precautions taken to avoid contamination.
• For 24-hour collection, patients are given a container with preservatives, and the container does not need to be sterile, only clean and dry.
• Urine specimens should be examined within 1 hour, or stored in 4-60C for a maximum of 8 hours, with preservatives used for 24-hour collections.

Learn about the physical, chemical, and microscopic examination of urine, and the formation of urine in the kidney through filtration, reabsorption, and secretion.