Color and transparency
Freshly voided urine is clear and pale to deep yellow. Its yellow color is due to urochrome, a pigment that results from the body’s destruction of hemoglobin. The more concentrated the urine, the deeper the yellow color.
An abnormal color such as pink or brown, or smoky tinge, may result from eating certain foods (beets, rhubarb) or may be due to presence in the urine of bile pigments or blood. Additionally, some commonly prescribed drugs and vitamin supplements alter the color of urine. Cloudy urine may indicate a urinary tract infection.
Fresh urine is slightly aromatic, but if allowed to stand, it develops an ammonia odor as bacteria metabolize its urea solutes. Some drugs and vegetables alter the usual odor of urine, as do some disease. For example, in uncontrolled diabetes mellitus the urine smells fruity because of its acetone content.
Urine is usually slightly acidic (around pH 6), but changes in body metabolism or diet may cause the pH to vary from about 4.5 to 8.0 . A predominantly acidic diet that contains large amount of protein and whole wheat products produces acidic urine. A vegetarian (alkaline) diet, prolonged vomitting, and bacterial infection of the urinay tract all cause the urine to become alkaline.
Because urine is water plus solutes, a given volume has a greater mass than the same volume of distilled water. The ratio of the mass of an equal volume of distilled water is its specific gravity. The specific gravity of distilled water is 1.0 and that of urine ranges from 1.001 to 1.035, depending on its solute concentration.