Hypoproteinemia: investigation in Cats (Felis) | Vetlexicon
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Hypoproteinemia: investigation

ISSN 2398-2950


Introduction

  • Functions of plasma proteins are integrated and diverse.
  • Analysis of these proteins reveals the general status of body protein metabolism directly evaluating the systems involved including:
    • Hepatic.
    • Gastrointestinal.
    • Hemopoietic.
    • Renal.
  • A considerable amount of information can be gleaned by approaching the syndrome 'hypoproteinemia' in a logical structured manner.

Is the patient hypoproteinemic?

Artifact

  • Dilutional effects of intravenous fluid administration.

Pathophysiology

  • There is a diagnostic equilibrium between tissue protein and serum protein.
  • As serum protein decreases, tissue protein moves into the vascular space to compensate to maintain colloid oncotic pressure (COP).
  • Consequently a considerable loss of tissue protein may occur with only minor changes in concentration of plasma proteins.
  • Clinical signs may, therefore, only occur late in the disease process.

Signalment

Age

Clinical signs

  • Signs of hypoproteinemia:
    • Fluid extravasation.
    • Ascites.
    • Pleural effusion Pleural effusion.
    • Subcutaneous edema (rare in small animal).
    • Clinical examination may reveal signs of underlying disease, or signs secondary to hypoproteinemia.
    • Weight loss Weight loss.
    • Stunted growth.
    • Weakness.
    • Respiratory difficulty/distress.

Signs associated with underlying disease

  • May give some clue to etiology of hypoproteinemia:
    • Icterus (?hepatic).
    • Diarrhea (?gastrointestinal).
    • PU/PD (?hepatic/renal).

Diagnostic approach

Identify potential site of protein loss

False proteinuria may occur with alkaline urine, heart failure, fever and corticosteroid administration.

  • Gastrointestinal system (protein losing enteropathy (PLE) Protein-losing enteropathy:
    • May be signs relating to gastrointestinal system, eg diarrhea, vomiting, inappetence.
    • Often weight loss is the only presenting sign, even when alimentary disease is extensive.

Gastrointestinal losses usually only investigated once renal loss and hepatic dysfunction have been ruled out.

Only low protein after at least 1 day.

Laboratory investigation

Diagnostic imaging

  • Ultrasonography and radiography useful for assessing internal organs, eg liver, kidney and intestine, for evidence of diseases.
  • Functional studies can be performed at specialist centers using scintigraphy to detect early organ dysfunction, eg hepatic scintigraphy Scintigraphy: hepatic function or renal scintigraphy Scintigraphy: renal for GFR.

Biopsy

  • Usual method of diagnosing cause of hypoproteinemia.
  • Hepatic, renal, or intestinal.

Other investigations

Not available for use in general practice.

  • Cr labeled albumin for gastrointestinal loss.
  • Sugar probes comparison of monosaccharide and disaccharide ratios, eg lactulose and rhamnose.
  • Breath hydrogen.

Causes of hypoproteinemia

Hemorrhage

  • Hypoproteinemia may appear more severe if fluids have been administered.

Plasma protein concentrations increase within 2-3 days and return to normal before hematocrit, RBC and HB.

Dietary

  • Malabsorption/maldigestion.
  • Ingestion of poor quality food.
  • Anorexia Anorexia secondary to other disease.
  • Changes are generally subtle but severe protein restriction  →  hypoproteinemia and hypoalbuminemia.

Protein losing enteropathy

  • Abnormal loss associated with:
  • May be no clincial signs if loss occurs gradually and compensatory mechanisms operate.
  • Albumin and globulin are more likely to both be reduced than in other causes of hypoproteinemia.
  • In more severe lesions there may be concurrent globulin loss.

Hepatic disease

  • The liver is the sole site of albumin synthesis and therefore albumin concentration gives a crude estimation of hepatic function.
  • Protein synthesis is one of the last hepatic functions to fail.
  • Albumin is usually normal in acute hepatic diseases because its half-life is 7-10 days.
  • Albumin:globulin ratio may be further increased by increased production of immunoglobulin.
  • Alterations reflecting a response of the reticuloendothelial system to antigenic stimulation.

Protein losing nephropathy

  • Only certain types of renal disease are associated with PLN, and amyloidosis Amyloidosis rarely causes hypoproteinemia in cats.
  • Glomerulonephritis Glomerulonephritis is almost always the cause.
  • Tubular lesions can occasionally  →  proteinuria.
  • Chronic renal failure may or may not be associated with PLN but these patients may be anorexic and suffering from protein malnutrition.
  • Albumin loss is usually greater and starts earlier than globulin due to small molecular size.

Third space

  • Body cavity effusion.
  • Vasculopathy.
  • This cause is minor and usually only documented with exudative cavity fluids, eg septic peritonitis Peritonitis, pyothorax Pyothorax.

Acute phase reaction

  • Albumin is mildly decreased in acute tissue injury or inflammation. It is a negative acute phase reactant.
  • This decrease is offset by increased positive acute phase reactants in alpha and beta globulin fractions, and hypoproteinemia does not usually occur.

Further Reading

Publications

Refereed papers

Other sources of information

  • Ettinger S J, Feldman E C, Cote E (eds) (2017) Textbook of Veterinary Internal Medicine. 8th edn. St Louis: Elsevier.
  • Stockham S L, Scott M A (2002) Fundamentals of Veterinary Clinical Pathology. Iowa: Iowa State Press.