Alpha-1 antitrypsin

Ranges vary between labs (some print 0.9 to 1.9, others 1.1 to 2.1) and it rises in pregnancy, on the combined pill and during any inflammation.

Alpha-1 antitrypsin is a protein made by the liver that protects the lungs and other tissues from damage by the body's own enzymes. Some people inherit a version that is made in smaller amounts or gets stuck inside liver cells. The test measures the amount of the protein in a blood sample; a separate test looks at the inherited type.

Doctors request it when someone has emphysema or breathlessness at a young age or without smoking, when liver tests are unexplained, and when a family member is known to carry the inherited trait. A low level usually leads on to a genetic type (phenotype) test.

• Any infection or inflammation, because it is an 'acute phase' protein
• Pregnancy and oestrogen-containing medicines
• Some cancers and long-term inflammatory conditions
• Smoking, by a small amount

• Inherited alpha-1 antitrypsin deficiency
• Severe liver disease
• Kidney conditions where protein leaks into the urine
• Severe malnutrition

• A cold or any inflammation can lift a genuinely low level into the range, masking a deficiency; doctors often check CRP at the same time
• Pregnancy and the combined pill raise it
• Different labs use different units and ranges

No fasting needed. Best measured when well, as inflammation raises it. A level result is usually paired with a phenotype or genotype test.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.