Urinalysis
An important part of urinalysis is the diagnosis of diseases in the kidney.
▪Blood is filtered in the kidneys
▪Waste products are removed and essential nutrients are reabsorbed
▪Urine is transported via the ureter to the bladder
Nephrons are the main functional units of the kidneys, basically they are responsible for filtering and reabsorption. It’s important to understand the basic nephron structure.
Perspective Note
A normal kidney has about 1 million nephrons.
Nephron:
The glomerulus consisting of a capillary network is the specific site of filtration. Particles that have a molecular weight (MW) over 50,000 will not pass through (eg albumin). 80% of the filtrate in the proximal tubule will be reabsorbed in the surrounding blood vessels. Water is reabsorbed during flow through the loop of Henle, distal tubule, and collecting duct.
Injury to the glomerulus allows cells and protein to enter the urinary tract. Infection in the renal system can lead to WBCs and/or bacteria in the urine.
Tubular disease will allow the passage of renal epithelial cells into the urine.
In the clinical lab, urine samples are centrifuged and the sediment is examined microscopically. Urine sediment structures include WBCs, RBCs, epithelial cells, oval fat bodies, casts, and crystals.