Urine For Specific Gravity and Its Significance

Sample
- A random urine sample can be taken.
Indications
- Urine analysis is part of the routine diagnostic profile.
- This gives an idea about kidney function.
- This also gives an idea about the hydration status.
Precautions
- Urine collected after the I/V administration of iodine-containing radiopaque material gives high values of specific gravity.
- Glucose and the protein in the urine also give high value.
- Diabetic patient with hyperglycemia gives high value.
Pathophysiology
- Urine-specific gravity is the measure of the kidney’s ability to concentrate the urine.
- The important process of reabsorption by the kidneys is often the first renal function to become impaired.
- So the specific gravity will detect dehydration or abnormality in the antidiuretic hormone.
- Urine is a solution of minerals, salts, and other compounds dissolved in water.
- Specific gravity = water + dissolved chemicals.
- So the specific gravity is the measure of the density of dissolved substances in the urine.
- Specific gravity is the weight of urine compared to distilled water, which has a specific gravity of 1.000.
- The specific gravity of the plasma entering the glomerulus is 1.010.
- Types of urine according to the specific gravity:
- Isosthenuria is the urine that has not greater and not less than the protein-free plasma.
- It is urine with a specific gravity of 1.010 (1.008 to 1.012).
- Hyposthenuria = specific gravity <1.010.
- Hyperstheuria = specific gravity is > 1.010.
- Random sample = 1.003 to 1.035.
- Most random sample = 1.015 to 1.025.
- The specific gravity of 1.023 or higher is generally considered normal.
- Specific gravity >1.035 is usually seen in the renal pyelogram (IVP).
- Specific gravity <1.003 is not urine.
- Isosthenuria is the urine that has not greater and not less than the protein-free plasma.
- Specific gravity depends upon :
- The state of hydration.
- Urine volume.
- High specific gravity indicates concentrated urine.
- Low specific gravity indicates dilute urine.
- The reflectometer can read specific gravity.
Normal
Source 2
- Adult = 1.005 to 1.030.
- Usually, it is 1.010 to 1.025
- Newborn = 1.001 to 1.020.
- For older adults, its value decreases.
- concentrated urine = 1.025 to 1.1030 or more
- Diluted urine = 1.001 to 1.010
Lab procedure to find specific gravity of urine:
- The Hydrometer checks the specific gravity but needs an abundant quantity of urine.
- Absorbent cellulose strip impregnated with bromthymol blue, polymethyl vinyl ether, and or maleic anhydride and sodium hydroxide.
- Color changes dark blue at low specific gravity 1.000.
- Yellow-green at a specific gravity of 1.030.
- Machine-readable devices are available from the Clinitek system, Bayer Diagnostics, and Elkhart Ind.
- If the urinometer does not measure the specific gravity, then dilute urine 1:2.
- Now multiply the reading by 2.
The Increased specific gravity is seen in:
- Dehydration.
- Decreased renal blood flow.
- Diabetes mellitus.
- Excessive water loss in fever, vomiting, and diarrhea.
- Toxemia of pregnancy.
- Congestive heart failure.
- Proteinuria.
- Water restriction.
The Decreased specific gravity is seen in:
- Diabetes insipidus.
- Early chronic failure.
- Severe renal damage.
- Hypertension.
- Overhydration.
- Diuresis.
Normal urine picture:
Physical features Chemical features Microscopic findings - Color = Pale yellow or amber
- Appearance = Clear to slightly hazy
- pH = 4.5 to 8.0
- Specific gravity = 1.015 to 1.025
- Blood = Negative
- Glucose = Negative
- Ketones= Negative
- Protein = Negative
- Bilirubin = Negative
- Urobilinogen = Negative (±)
- Leucocyte esterase = Negative
- Nitrite for bacteria = Negative
- RBCs = Rare or Negative
- WBC = Rare or Negative
- Epithelial cells = Few
- Cast = Negative (Occasional hyaline)
- Crystal = Negative (Depends upon the pH of the urine)
- Bacteria = Negative