133 Serum albumin (ALB)

Serum albumin: functions, causes of low albumin (liver, kidney, inflammation, nutrition) and prognostic meaning.

Serum albumin is the most abundant protein in the blood, made only by the liver, about 10–15 g a day. It maintains plasma oncotic pressure, which keeps fluid inside the vessels. It also carries hormones, fatty acids, bilirubin, calcium and many drugs, and acts as an antioxidant. Albumin has a half-life of about three weeks, so it reflects longer-term conditions. It falls in liver disease, kidney and gut losses, malnutrition, and in any significant inflammation, because it is a "negative acute-phase protein".

Blood proteinsLiver functionNutrition and inflammation

Adults35–50 g/L (3.5–5.0 g/dL)

Low< 35 g/L

Oedema likelyusually < 25 g/L

Half-life≈ 3 weeks

Figure 1. Albumin zones. High albumin almost always reflects dehydration rather than overproduction.

Causes of low albumin

Mechanism	Examples
Reduced synthesis	Liver cirrhosis, acute and chronic inflammation, malnutrition, malabsorption
Increased loss	Nephrotic syndrome and other kidney diseases with albuminuria, protein-losing enteropathy, burns, large wounds
Redistribution, dilution	Sepsis and capillary leak, ascites, heart failure, intravenous fluids, pregnancy

Clinical significance

Low albumin is a strong marker of poor prognosis in hospitalised patients, liver cirrhosis, heart failure and kidney disease, often more because of the underlying illness and inflammation than because of albumin itself. Albumin is part of liver function scores (Child–Pugh). It affects the interpretation of calcium, because total calcium falls with low albumin, and the effect of protein-bound drugs. Very low albumin contributes to oedema and ascites.

What to do

A low albumin should be explained: liver tests, urine protein or albumin, inflammation markers (CRP) and nutritional assessment. Leg swelling, foamy urine, weight loss or chronic diarrhoea are reasons to see a doctor soon.

References

Busher JT. Serum albumin and globulin. In: Walker HK, Hall WD, Hurst JW, eds. Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd ed. Boston: Butterworths; 1990. Chapter 101. ncbi.nlm.nih.gov/books/NBK204
Kwo PY, Cohen SM, Lim JK. ACG clinical guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35. doi:10.1038/ajg.2016.517

This article is for general information and does not replace a consultation with a doctor. Laboratory results must be interpreted by a physician together with symptoms and other tests.

Published on 12 May 2024