Body Fluids & Urinalysis

Pale-yellow to amber. The principal pigment is urochrome, a product of endogenous metabolism; smaller contributions come from uroerythrin and urobilin. Color intensity roughly tracks specific gravity (concentration).

Red urine can result from RBCs (hematuria), free hemoglobin (hemoglobinuria), myoglobin (myoglobinuria), beeturia (beets in genetically susceptible people), porphyrins, rifampin, or phenazopyridine (orange-red). Microscopic exam and a plasma check help distinguish them.

Reported as clear, hazy, cloudy, turbid, or milky. Cloudiness can come from RBCs, WBCs, bacteria, epithelial cells, crystals, mucus, lipids (chyluria/lipiduria), or amorphous precipitates. Normal fresh urine is usually clear.

Specific gravity compares urine density to that of an equal volume of water; it reflects the kidney's ability to concentrate. Random urine typically runs 1.003–1.035, with normal adults around 1.015–1.025. Values track solute concentration.

Isosthenuria is a fixed specific gravity near 1.010, matching the specific gravity of the glomerular filtrate (plasma ultrafiltrate). It indicates the kidney has lost both concentrating and diluting ability, seen in chronic renal failure.

A refractometer measures refractive index (total solute mass) and is affected by glucose, protein, and radiographic contrast media. The reagent strip measures ionic solutes only via a pKa change of a polyelectrolyte; it is not affected by glucose, urea, or contrast but is influenced by pH.