Specific Gravity of Blood

Specific gravity is the ratio of weight of a given volume of a fluid to the weight of the same volume of distilled water measured at 25^°C. Plasma protein concentration is largely responsible for the specific gravity of the plasma. The cellular elements called the corpuscles have higher specific gravity than the plasma.

Species	Specific gravity
Goat	1.042 (1.036 – 1.051)
Pig	1.045 (1.035 – 1.055)
Dog	1.048 (1.045 – 1.052)
Cat	1.050 (1.045 – 1.057)
Sheep	1.051 (1.041 – 1.061)
Cattle	1.052 (1.046 – 1.061)
Horse	1.053 (1.046 – 1.059)

The copper sulphate drop falling method is commonly used for the assessment of specific gravity of blood and plasma. Various factors influence the specific gravity of the blood.

Specific gravity of blood is increased in the following conditions:

1. Polycythemia: High altitude, polycythemia vera, newborns etc.
2. Severe dehydration: Excessive fluid loss such as in vomiting, diarrhoea.
3. Hemoconcentration: Loss of plasma as in burns.

Specific gravity of blood is decreased in the following conditions:

1. Pregnancy: Increase in plasma volume causes hemodilution.
2. Anaemia.
3. Renal diseases: Loss of albumin, oedema etc.
4. Hemodilution: Hypersecretion or prolonged treatment with glucocorticoids.
5. Starvation and malnutrition: Decrease in plasma protein.
6. Intravenous fluid transfusions.