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Urinalysis: specific gravity

ISSN 2398-2969

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Synonym(s): Relative density

Overview

  • Measurement of 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.

Sampling

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Tests

Methodologies

Refractometer Refractometer 
  • Most common method.
  • If crystal sludging present, urine should be spun in a centrifuge with a supernatant assessed for specific gravity.
  • Single drop placed on glass surface; reading relative so specific gravity of distilled water (=1).
  • Crystalluria does not appear to interfere with reading.
Dipstick Urinalysis: dipstick analysis
  • Results do not correlate well with refractometer.
  • Inaccurate for non-human urine/disregard for animal urine.

Availability

  • Standard practice laboratory technique.

Validity

Sensitivity

  • Good with refractometer.
  • Poor with dipstick.

Specificity

  • Good with refractometer.
  • Poor with dipstick.

Predictive value

  • Must be interpreted alongside blood biochemistry Blood biochemistry: overview.
  • Dipstick results are inaccurate, refractometer should be used.

Technique intrinsic limitations

  • Cannot interpret results in isolation from other urinalysis results and lab tests.
  • Single random result outside normal reference range cannot establish diagnosis.
  • Glycosuria above 3+ may result in false elevation of urine specific gravity.

Technician extrinsic limitations

  • Refractometer must be calibrated using distilled water before use.

Result Data

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Further Reading

Publications

Refereed papers

Other sources of information

  • Varga M (2014) Textbook of Rabbit Medicine. 2nd edn. Butterworth-Heinemann, UK.
  • Chitty J & Carmichael N (2012) Laboratory techniques. In: BSAVA Manual of Exotic Pet and Wildlfe Nursing. Eds: Varga M, Lumbis R & Gott L. BSAVA, UK.
  • Quesenberry K E & Carpenter J W (2012) Ferrets, Rabbits and Rodents. In: Clinical Medicine and Surgery. 3rd edn. Elseveier-Saunders, USA.
  • Saunders R A & Rees Davies R (2005) Notes on Rabbit Internal Medicine. Blackwell Publishing, UK.
  • Harcourt-Brown F (2002) Textbook of Rabbit Medicine. Elsevier, UK.