Urine For Specific Gravity and Its Significance

Sample

• A random urine sample can be taken.

Indications

1. Urine analysis is part of the routine diagnostic profile.
2. This gives an idea about kidney function.
3. This also gives an idea about the hydration status.

Precautions

1. Urine collected after the I/V administration of iodine-containing radiopaque material gives high values of specific gravity.
2. Glucose and the protein in the urine also give high value.
3. Diabetic patient with hyperglycemia gives high value.

Pathophysiology

1. Urine-specific gravity is the measure of the kidney’s ability to concentrate the urine.
   1. The important process of reabsorption by the kidneys is often the first renal function to become impaired.
   2. So the specific gravity will detect dehydration or abnormality in the antidiuretic hormone.
2. Urine is a solution of minerals, salts, and other compounds dissolved in water.
   1. Specific gravity = water + dissolved chemicals.
3. So the specific gravity is the measure of the density of dissolved substances in the urine.
4. Specific gravity is the weight of urine compared to distilled water, which has a specific gravity of 1.000.
5. The specific gravity of the plasma entering the glomerulus is 1.010.
6. Types of urine according to the specific gravity:
   1. Isosthenuria is the urine that has not greater and not less than the protein-free plasma.
      1. It is urine with a specific gravity of 1.010 (1.008 to 1.012).
   2. Hyposthenuria = specific gravity <1.010.
   3. Hyperstheuria = specific gravity is > 1.010.
   4. Random sample = 1.003 to 1.035.
      1. Most random sample = 1.015 to 1.025.
      2. The specific gravity of 1.023 or higher is generally considered normal.
      3. Specific gravity >1.035 is usually seen in the renal pyelogram (IVP).
   5. Specific gravity <1.003 is not urine.
7. Specific gravity depends upon :
   1. The state of hydration.
   2. Urine volume.
8. High specific gravity indicates concentrated urine.
9. Low specific gravity indicates dilute urine.
10. 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:

1. The Hydrometer checks the specific gravity but needs an abundant quantity of urine.

2. Absorbent cellulose strip impregnated with bromthymol blue, polymethyl vinyl ether, and or maleic anhydride and sodium hydroxide.
   1. Color changes dark blue at low specific gravity 1.000.
   2. Yellow-green at a specific gravity of 1.030.
3. Machine-readable devices are available from the Clinitek system, Bayer Diagnostics, and Elkhart Ind.
4. If the urinometer does not measure the specific gravity, then dilute urine 1:2.
   1. Now multiply the reading by 2.

The Increased specific gravity is seen in:

1. Dehydration.
2. Decreased renal blood flow.
3. Diabetes mellitus.
4. Excessive water loss in fever, vomiting, and diarrhea.
5. Toxemia of pregnancy.
6. Congestive heart failure.
7. Proteinuria.
8. Water restriction.

The Decreased specific gravity is seen in:

1. Diabetes insipidus.
2. Early chronic failure.
3. Severe renal damage.
4. Hypertension.
5. Overhydration.
6. 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

    

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