Physical Properties of Urine

Physical properties include:

Color

Color is influenced by metabolism, physical activity, diet, and pathologic conditions
Pigments in urine:
- Urochrome - responsible for yellow pigment
- Urobilin - responsible for orange/yellow pigment
- Uroerythrin - responsible for red/pink pigment
Light yellow - recent fluid consumption, polyuria, or diabetes
Dark yellow - first morning pee or dehydration
Amber/Orange
- Bilirubin if there is yellow foam
- Urobilinogen if there is no yellow foam
- Pyridium is a common UTI medication
Yellow-green - bilirubin oxidized into biliverdin
Green - pseudomonas infection
Blue-green - medical dyes
Pink - RBCs
Red
- Cloudy - RBCs
- Clear - hemoglobin/myoglobin
Brown - RBCs oxidized into methemoglobin
Black - malignant melanoma, homogentisic acid, or methemoglobin

Clarity

Clarity of urine ranges from clear, hazy, cloudy, turbid, to milky
Some nonpathogenic causes of turbidity indicated in alkaline urine are:
- Squamous epithelial cells and mucus in female specimens
- Bacterial growth from contamination
- Amorphous phosphates from refrigerated samples
- Contamination
Some pathogenic causes of turbidity are:
- RBCs, WBCs, and bacteria
- Nonsquamous epithelial cells
- Yeast
- Crystals
- Lipids

Specific Gravity

Specific gravity is the evaluation of urine concertation
- Normal SG range is 1.015-1.025
  - Isosthenuric - SG of 1.010
  - Hyposthenuric - SG < 1.010
  - Hypersthenuric - SG > 1.010
The refractometer measures velocity of light in air versus velocity of light in a solution
- Calibrated using distilled water and sodium chloride
Exceptions of specific gravity calculation:
- Protein - subtract 0.003 for each gram of protein
- Glucose - subtract 0.004 for each gram of glucose
Abnormally high results (> 1.040) are usually due to radiographic contrast media

Odor