Definition: Albumin is the main protein in the liquid part of blood, and an albumin blood test measures how much of that protein is circulating in the bloodstream.
What is albumin and what does it do?
Albumin is a protein made by the liver and is the most abundant protein in blood plasma. MedlinePlus says albumin helps keep fluid from leaking out of blood vessels and helps carry substances such as hormones, vitamins, and enzymes around the body. Lab Tests Online UK adds that albumin also helps maintain acid-base balance and transport minerals such as calcium.
That fluid-balance role is why very low albumin can be linked with swelling, fluid leakage, or oedema. Albumin acts a bit like a circulating sponge that helps hold water inside the bloodstream. This is also why albumin is not just a “liver number.” It reflects protein production, protein loss, fluid balance, and whole-body illness.
Why is albumin tested?
Albumin is often checked as part of liver function tests or a comprehensive metabolic panel rather than as a standalone test. MedlinePlus says albumin is used to check general health and nutrition and to see how well the liver and kidneys are working. It may also be used to monitor treatment in liver or kidney conditions and is commonly included in liver panels.
Lab Tests Online UK similarly says albumin is one of the most commonly requested blood tests and is usually measured as part of a broader panel. It may be ordered when liver disease, kidney disease, serious infection, inflammatory illness, hospital admission, or pre-operative assessment is being considered.
What does low albumin mean?
Low albumin, or hypoalbuminaemia, is much more common than high albumin. MedlinePlus says lower-than-normal albumin may be seen in liver disease, kidney disease, malnutrition, infection, digestive diseases with poor protein use, burns, and thyroid disease. Lab Tests Online UK gives similar categories and adds that nephrotic syndrome is a classic kidney-loss example because damaged glomeruli can let albumin leak into urine.
The key message is that low albumin does not tell you one single diagnosis. Instead, it raises broader questions: Is the liver making less albumin? Are the kidneys leaking albumin? Is there inflammation or serious illness? Is the person undernourished or not absorbing nutrients well? Is dilution or fluid balance part of the picture? That is the right mental model for patients and for students — albumin is a context marker.
What does high albumin mean?
High albumin is less common. MedlinePlus says higher-than-normal albumin may be a sign of dehydration. Lab Tests Online UK says the same and explains that when there is less water in the bloodstream, albumin becomes more concentrated. Common contributors include poor fluid intake, severe vomiting or diarrhoea, heavy sweating, or diuretic use.
So if albumin is high, the question is usually not “Why is the body making too much albumin?” It is more often “Is the blood more concentrated because of fluid loss?”
Albumin interpretation table
This is a general educational table. Exact reference intervals vary by laboratory, assay method, age, pregnancy status, and clinical context.
| Result | Typical range (UK) | What it may suggest |
|---|---|---|
| Low (hypoalbuminaemia) | Below 35 g/L | Liver disease, kidney loss, malnutrition, inflammation, serious illness |
| Normal | 35–50 g/L | Within expected range for most adults |
| High | Above 50 g/L | Usually dehydration — blood is more concentrated |
Reference ranges vary by laboratory and method. Pregnancy lowers albumin physiologically. Always refer to your own laboratory’s reference interval.
| Albumin pattern | What it may suggest | Main reminder |
|---|---|---|
| Low albumin | Reduced liver production, kidney loss, inflammation, malnutrition, or fluid dilution may be considered | Albumin alone cannot diagnose the cause |
| Normal albumin | Liver production and retention may be broadly adequate | Normal albumin does not rule out all liver or kidney disease |
| High albumin | Dehydration or haemoconcentration is often considered | Usually a fluid-balance issue rather than “too much albumin production” |
Why albumin is often interpreted with liver and kidney tests
Albumin is made by the liver and retained by healthy kidneys. That is why it often sits in both liver and kidney conversations. MedlinePlus says albumin blood testing is frequently part of a liver panel, while Lab Tests Online UK says low albumin may lead to further liver function testing, kidney function tests, urine albumin-creatinine ratio, protein electrophoresis, or inflammatory markers depending on the clinical picture.
Pre-analytical issues and factors that affect albumin
Albumin is useful, but it is sensitive to context. MedlinePlus says certain medicines, including steroids, insulin, and hormones, can increase albumin, while albumin can be lower if the person has not eaten for 24 to 48 hours, is pregnant, or is taking some medicines such as birth control pills. Lab Tests Online UK adds several practical influences: IV fluids can dilute albumin, posture can matter because albumin is slightly higher when standing than lying down, hydration affects concentration, pregnancy lowers albumin physiologically, and albumin may be slightly lower in older adults.
What happens during the test?
Albumin is measured from a routine venous blood sample. MedlinePlus says no special preparation is usually needed for albumin alone, although fasting may be required if other blood tests are being collected at the same time. Lab Tests Online UK also says no fasting or special preparation is usually needed, while reminding readers to mention medicines that may affect the test.
Albumin is not the same as urine albumin
Worth making this clear: a blood albumin test is different from a urine albumin or urine albumin-creatinine ratio test. Lab Tests Online UK says urine albumin testing helps detect albumin leaking through damaged kidneys, while blood albumin reflects the concentration of albumin circulating in plasma. Same protein, different sample, different question.
Practical takeaway
Albumin is one of those simple-looking lab numbers that quietly tells you a lot. Low albumin often prompts review of liver production, kidney loss, inflammation, nutrition, and fluid balance. High albumin usually points more toward dehydration. Albumin is best treated as a context protein, not a one-number diagnosis tool.
Frequently asked questions
What does an albumin blood test measure?
It measures the amount of albumin, the main plasma protein, in the blood.
What causes low albumin?
Low albumin may be linked with liver disease, kidney disease, inflammation, infection, malnutrition, digestive disorders, burns, or fluid dilution.
Is high albumin dangerous?
High albumin is less common and is most often linked with dehydration rather than excess protein production.
Do I need to fast for an albumin blood test?
Usually not for albumin alone, but fasting may be required if it is being done with other tests at the same time.
Is blood albumin the same as urine albumin?
No. Blood albumin measures albumin circulating in the blood. Urine albumin tests look for albumin leaking into urine, which can suggest kidney damage.
Educational only. This page does not provide diagnosis, treatment, or personal medical advice.
Sources: MedlinePlus — Albumin Blood Test | Lab Tests Online UK — Albumin
How albumin relates to other tests
- Liver function tests — albumin is routinely reported alongside ALT, ALP, bilirubin and total protein. See: Liver Function Test Explained
- eGFR and kidney function — nephrotic syndrome causes albumin to leak into urine alongside reduced eGFR. See: eGFR Explained
- CRP — albumin falls and CRP rises in acute inflammation — opposite directions, same cause. See: CRP Blood Test Explained
- Calcium — calcium is partially bound to albumin; low albumin can affect total calcium interpretation. See: Calcium Blood Test Explained
- Bone profile — albumin is included in bone panels because of its calcium-binding role. See: Bone Profile Blood Test Explained