Azotemia

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Introduction

  • Azotemia is an increased concentration of nonprotein nitrogenous compounds (eg urea and creatinine) in the blood. "Uremia" is the clinical syndrome that occurs as a result of severe azotemia due to abnormal renal function.
  • Causes:
    • Reduced glomerular filtration rate:
      • Reduced renal perfusion (- pre renal azotemia    );
      • Primary renal disease (renal azotemia  [Uremia]  );
      • Obstruction to urinary outflow (post-renal azotemia).
    • Uroabdomen leading to reabsorption of urinary nitrogenous compounds (post-renal azotemia).
    • Increased absorption of nonprotein nitrogenous compounds from the gastro-intestinal tract, eg GI bleeding, high protein meal.
    • Increased protein catabolism, eg fever, trauma, burns    , hyperthyroidism    .
  • A degree of pre-renal azotemia may be super-imposed on pre-existing renal or post-renal azotemia.

Diagnosis

Clinical signs

  • Signs referable to the underlying cause, and additionally:
    • Evidence of dehydration, nausea, poor coat quality.
    • Uremic breath, weakness.
    • Hypersalivation, uremic stomatitis, ataxia, stupor.

Diagnosis

Differential diagnosis

  • Differentiation of Renal and Pre-renal azotemia:
    • Assess both azotemia and urine specific gravity    :
      • Azotemia and urine SG <1.035 (before administration of any fluid therapy) indicates an element of renal dysfunction, with or without concurrent pre-renal azotemia.
      • Azotemia and urine SG >1.045 indicates pre-renal azotemia with an appropriate renal compensatory response.  Threat with intravenous fluids and re-assess the azotemia once hydration status has been corrected.
      • Azotemia and urine SG 1.035-1.045 is likely to be due to a combination of primary renal disease and pre-renal azotemia.  Treat with intravenous fluids and re-assess the azotemia once hydration status has been corrected.  If azotemia resolves completely renal function is likely to be adequate, although a degree of renal compromise is not ruled out.
      • Azotemia and hyposthenuria SG <1.007 : despite the dilute urine, the azotemia is most likely prerenal; a consequence of massive, obligatory polyuria with inadequate compensatory drinking. There is a separate cause for the hyposthenuria (eg liver disease, nephrogenic diabetes insipidus or central diabetes insipidus     (the latter being rare in cats). Reassess the azotemia after the animal has received appropriate fluid therapy.

Outcomes

Prognosis

  • Depends on the underlying cause of the azotemia.
  • If pre-renal and post-renal azotemia can be managed effectively a full recovery is possible, but both conditions have the potential to cause permanent renal damage if severe enough, or if left untreated for too long.
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