Urinalysis: specific gravity

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Sections available in full article Overview, Uses, Sampling, Source of test material, Quantity of test material, Quality control, Test (s), Methodologies, Availability, Technique (intrinsic) limitations, Result data, Normal (reference) values, Abnormal values, Errors and Artifacts, Sources, Publications, Vetstream contributor(s),
Contributors Dr Kathleen P Freeman DVM MS PhD MRCVS

Overview

  • Measure kidneys' ability to concentrate and dilute urine.

Uses

Alone

  • Assessment of kidneys' ability to alter specific gravity of glomerular filtrate.

In combination

  • With other tests of renal function in assessment of renal function.

Result data

Normal (reference) values

  • Usually a random urine specimen from an animal with normal renal function has specific gravity >1.030.
  • Maximum reference range: 1.001-1.065.
  • Note that glomerular filtrate: 1.008-1.012 = isosthenuria.

Abnormal values

Persistent hyposthenuria Hyposthenuria suggests that renal failure is not present (reflects renal function in dilutions of urine)
  • Increased loss of water without increased loss of solute = polyuria, eg:
    • Diabetes insipidus Diabetes insipidus.
    • Hyperadrenocorticism Hyperadrenocorticism.
    • Pyometra Pyometra.
    • Hypercalcemia Hypercalcemia: overview.

Normal - slightly raised

  • Increased loss of water due to increased loss of solute = polyuria, eg:
    • Increased salt or protein intake.
    • Osmotic diuretics, eg mannitol Mannitol.
    • Diabetes mellitus Diabetes mellitus.

Persistently raised

  • Decreased loss of water without decreased loss of solutes = poor renal perfusion, eg:
    • Severe dehydration.
    • Severe hemorrhage.
    • Reduced cardiac output, eg heart failure Congestive heart failure , shock Shock , obstructed renal vessels (thrombi, infarct Kidney: thromboembolismKidney: ischemia ).

Fixed (persistently isosthenuric)

  • Reduced ability to concentrate or dilute glomerular filtrate = renal failure (acute Kidney: acute renal failure or chronic Chronic renal failure ).

Errors and Artifacts

  • Increase in refractometer reading with dextran Dextrans and also sometimes glucose Glucose and radiographic contrast agents.
  • Decrease with corticosteroids Hydrocortisone , diuretics Therapeutics: urinary system and fluid therapy Fluid therapy.

Sources

Publications

Refereed papers

  • Brobst D (1989) Urinalysis and associated laboratory procedures. Vet Clin North Am Small Anim Pract 19 (5), 929-949.
  • McCaw D L, Fleming E J & Mikiciuk M G (1989) Interpreting the results of urinalysis - a key to diagnosing renal disorders. Vet Med 84 (3), 281-286.

Other sources of information

  • Kaneko J J (1997) Clinical Biochemistry of Domestic Animals. 5th edn. Harvey J W & Bruss M L (eds). Academic Press, Boston.
  • Duncan J R, Prasse K W & Mahaffy E A (1994) Veterinary Laboratory Medicine Clinical Pathology. 3rd edn. Iowa University Press, Ames, Iowa.

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