Discuss specific gravity, appearance, color, and pH of urine and the information we can learn from these assessments.

Discuss specific gravity, appearance, color, and pH of urine and the information we can learn from these assessments.

Urine color ranges from yellow to amber depending on urine concentration and the presence of pigment urochrome. From ancient times, the color of urine has been an important diagnostic tool, with 20 colors in 100 BC (3). Foods, medications, metabolic products and infections change the color (1). This article has pictures and descriptions of different colored urine.  (3)

Urine outside of the body will develop ammonia smell as bacteria break up urea molecules. Fresh urine with same smell often indicates infection with bacterial working in the bladder (2).

Urine specific gravity provides insight into patient’s hydration status and correlates with urine osmolality and the kidney’s capability in concentrating fluids (1). Normal urine USG is greater than 1.000 as the kidney removes water AND minerals, salts, and other compounds (1). The more additives to water, the higher the USG which normally can rise to 1.030 (2). Above 1.030 there is typically glucose or protein added, the syndrome of inappropriate antidiuretic hormone, or the patient’s is dehydrated (1,2). Overhydrated patients typically have USG value closed to water; other causes include diuretic use, diabetes insipidus, adrenal insufficiency, aldosteronism, impaired renal function (2).

Urine pH ranges from 4.5 to 8, and typically mirrors the plasma pH (except for cases of Renal Tubular Acidosis) (2). Typically, the serum (reflected in the glomerular filtrate) pH is around 7.4, and the kidneys with acidify to approximately 6.0 (1). The kidneys sensing and excreting excess alkali (bicarbonate or excess acid (hydrogen or ammonia) in the urine is a major way the body maintain acid-base balance (1). Other factors may cause variations in pH of urine: In cases of urinary tract infections, an elevated pH suggests the presence of bacteria that area splitting urea (2). More alkaline urine may be found in vegetarians who consume citrus fruits, legumes, and vegetables (1). Meat eaters, or those consuming cranberry juice, tend to have more acidic urine (1).

Urine pH is helpful in treating urine calculi: “Calcium phosphate, calcium carbonate, and magnesium phosphate stones develop in alkaline urine; when this occurs, the urine is kept acidic. Uric acid, cystine, and calcium oxalate stones precipitate in acidic urine; in this situation, the urine should be kept alkaline or less acidic than normal” (1).

(1)   RhCeus.com: Urinary ph. http://www.rnceus.com/course_frame.asp?exam_id=23&directory=ua

(2)   JEFF A. SIMERVILLE, M.D., WILLIAM C. MAXTED, M.D., and JOHN J. PAHIRA, M.D. Urinalysis: A Comprehensive Review. Am Fam Physician. 2005 Mar 15;71(6):1153-1162.