Synonyms: Albuminaemia (in plasma); albuminuria, microalbuminuria (in urine)
Related tests: Creatinine, Urea, eGFR, Uric acid, Urine protein, complete urine test
Clinical significance
Albumin is the most abundant protein in plasma; it is small and is made by the liver, so in severe liver failure plasma albumin levels fall. Severe nutritional deficiencies can of course also explain a general fall in circulating proteins, including albumin. Albumin has three functions: carrying metabolites that are insoluble in water (e.g. bilirubin, free fatty acids, thyroid hormones), maintaining oncotic pressure (essential for controlling fluid exchange between the capillaries and interstitial fluid) and acting as an amino acid reserve (it can enter cells and be broken down to allow other proteins to be made). Albumin turnover is high: 50% of the molecules produced are broken down within 10 days.
A fall in plasma albumin can be caused by insufficient production by the liver (cirrhosis), protein malnutrition (kwashiorkor) or excessive loss in the urine due to changes in the glomerular filter.
Clinical indications
Assessment of kidney function, diagnosis of oedema.
Sample type
The patient must have a blood sample taken.
Timed urine collection (to calculate the amount of albumin excreted per unit of time).
First morning urine (to normalise the albumin excreted to urinary creatinine).
Preparation
You must fast for at least 8 hours; a small amount of water is allowed. You must have been standing or sitting upright for at least 30 minutes.
For a timed urine collection, follow the instructions given by the laboratory.
Notes
It is advisable to measure albumin in the first morning urine, normalised to creatinine.
Urinary albumin excretion increases after intense physical exercise.
Albumin due simply to standing (orthostatic or postural proteinuria) can be distinguished from pathological albumin by analysing two samples: one collected in the morning immediately before getting out of bed and the second after at least 2 hours of standing.