Albumin
The most abundant protein in blood plasma, produced by the liver. Albumin maintains oncotic pressure, transports hormones and drugs, and serves as a clinical marker of liver function, nutritional status, and protein-losing diseases.
Albumin is the most abundant protein in canine blood plasma, constituting approximately 35-50% of total serum protein. It is synthesized exclusively by the liver at a rate that reflects both hepatic synthetic capacity and nutritional substrate availability. Normal canine serum albumin ranges from approximately 2.5-4.0 g/dL, depending on the laboratory.
Physiological Functions
Albumin serves multiple critical roles:
Oncotic pressure maintenance: Albumin is the primary determinant of plasma oncotic (colloid osmotic) pressure, which keeps fluid inside blood vessels. When albumin drops below approximately 1.5 g/dL, fluid leaks from the vasculature into tissues and body cavities, causing edema, ascites, and pleural effusion.
Transport: Albumin binds and transports hormones (thyroid, cortisol), fatty acids, bilirubin, calcium, and many drugs (NSAIDs, corticosteroids, antibiotics). Low albumin can alter the effective concentration and toxicity of protein-bound drugs.
Antioxidant and buffering: Albumin acts as a free radical scavenger and contributes to acid-base buffering in plasma.
Causes of Low Albumin (Hypoalbuminemia)
Decreased production: Liver disease — chronic hepatitis, cirrhosis, or portosystemic shunts — reduces hepatic albumin synthesis. The liver has significant reserve capacity, so hypoalbuminemia from liver disease indicates substantial loss of functional hepatic mass.
Gastrointestinal loss: Protein-losing enteropathy (PLE) causes loss of albumin through damaged intestinal mucosa. PLE is a significant diagnostic consideration in breeds like Soft-Coated Wheaten Terriers and Yorkshire Terriers.
Renal loss: Protein-losing nephropathy (PLN) allows albumin to leak through damaged glomerular filtration barriers. Urine protein:creatinine ratio (UPC) confirms renal protein loss.
Inflammatory bowel disease: Chronic intestinal inflammation can cause albumin loss through both mucosal leakage and reduced absorption of amino acid substrates.
Third-space losses: Peritonitis, vasculitis, and severe burns can shift albumin out of the vascular space.
Clinical Interpretation
Albumin is part of a standard serum chemistry panel. A single low value requires investigation, but trending albumin over serial tests is more informative. A progressive decline suggests worsening liver disease, ongoing GI or renal protein loss, or inadequate nutrition.
Albumin should always be interpreted alongside total protein, globulin fraction, liver enzymes, urinalysis, and clinical signs. Low albumin with normal or high globulins suggests chronic inflammation with protein loss. Low albumin with low globulins suggests non-selective protein loss (PLE or PLN).
Relevance to Longevity
Serial albumin monitoring through routine bloodwork is one of the earliest indicators of hepatic decline, occult GI disease, and nutritional insufficiency in aging dogs. Detecting a downward trend in albumin before clinical signs appear allows earlier diagnostic investigation and intervention.