Alpha-1 Antitrypsin Unit Converter
Alpha-1 Antitrypsin Unit Converter
Convert alpha-1 antitrypsin between mg/dL, g/L, mg/L and µmol/L, with the protective threshold and why an acute-phase rise can hide a deficient patient.
Alpha-1 Antitrypsin converter
Mass ⇄ molarAlpha-1 antitrypsin 120 mg/dL
Formula and conversion factors
mg/L = mg/dL × 10
µmol/L = mg/dL × 0.1923
- ÷ 100
- a decilitre is a tenth of a litre and a gram is 1000 mg, so 120 mg/dL is 1.20 g/L
- 0.192308
- derived from a molecular mass of 52,000 Da; because the protein is glycosylated and its mass varies with glycoform, treat the molar figure as nominal
- acute-phase reactant
- hepatic synthesis rises with inflammation, so a single level cannot exclude deficiency
- protective threshold
- about 0.5 g/L, or 50 mg/dL — the level below which the risk of emphysema is considered to rise
Worked example
Alpha-1 antitrypsin 120 mg/dL
120 ÷ 100 = 1.20 g/L
120 × 10 = 1,200 mg/L
120 × 0.1923 = 23.1 µmol/L (nominal)
Within the adult reference interval of 90–200 mg/dL
Thresholds across the units
| mg/dL | g/L | µmol/L | |
|---|---|---|---|
| Adult reference interval | 90 – 200 | 0.90 – 2.00 | 17.3 – 38.5 |
| Protective threshold — emphysema risk rises below | 50 | 0.50 | 9.6 |
| Typical of a severely deficient phenotype | < 50 | < 0.50 | < 9.6 |
What the level cannot tell you
| Situation | Level | What to do |
|---|---|---|
| Low level, no inflammation | < 90 mg/dL | Phenotype or genotype; do not simply repeat the level |
| Borderline level with a raised CRP | 90 – 110 mg/dL | The acute-phase rise may be masking deficiency — phenotype if suspicion is real |
| Normal level, strong clinical suspicion | Within range | Proceed to phenotyping or genotyping regardless of the level |
| High level | > 200 mg/dL | Acute-phase response; it says nothing about the underlying phenotype |
Why a normal level does not settle the question
Alpha-1 antitrypsin is reported in mg/dL in the United States and in g/L elsewhere, a factor of 100 apart, and occasionally in mg/L. A molar figure in µmol/L is sometimes seen, using a factor of 0.1923 derived from a molecular mass of 52,000 daltons. That figure should be read as nominal rather than exact: the protein is glycosylated, its mass varies with glycoform, and no clinical threshold is expressed in molar units, so the column is offered only for datasets that use it.
The central trap is that alpha-1 antitrypsin is an acute-phase reactant. Hepatic synthesis increases with inflammation, infection, pregnancy and oestrogen therapy, and the rise is large enough to lift a genuinely deficient patient into the reference range. A normal level therefore does not exclude deficiency, and a borderline level alongside a raised CRP should be read with real suspicion. Where the clinical question is serious, phenotyping by isoelectric focusing or genotyping for the common S and Z alleles is what answers it, and the level is at best a screen.
The threshold that matters is around 0.5 g/L, or 50 mg/dL, sometimes called the protective threshold. Below it, the antiprotease screen in the lung is considered insufficient to restrain neutrophil elastase and the risk of emphysema rises; above it, deficiency is unlikely to be doing pulmonary damage. It is a population-derived figure rather than a sharp biological boundary, and phenotype, smoking history and occupational exposure all modify the risk it describes.
Clinically, deficiency presents in two organs. In the lung it produces emphysema that is characteristically basal rather than apical and that appears decades early, especially in smokers, in whom the natural history is far worse. In the liver it produces neonatal cholestasis, and in adults chronic liver disease, cirrhosis and hepatocellular carcinoma, driven by polymerised Z protein retained within hepatocytes rather than by the deficiency itself. Testing is worth considering in any adult with early-onset or basal emphysema, unexplained liver disease, or an affected relative.
Frequently asked questions
How do I convert alpha-1 antitrypsin from mg/dL to g/L?
Divide by 100. A level of 120 mg/dL is 1.20 g/L, or 1,200 mg/L. Going the other way, multiply the g/L figure by 100.
Why is the µmol/L figure only nominal?
It uses a molecular mass of 52,000 daltons, but the protein is glycosylated and its mass varies between glycoforms. No clinical threshold is expressed in molar units, so the conversion is offered for completeness rather than for decision-making.
Does a normal alpha-1 antitrypsin level exclude deficiency?
No. It is an acute-phase reactant, so inflammation, infection, pregnancy or oestrogen can raise a deficient patient into the reference range. Where clinical suspicion is real, phenotyping or genotyping is required regardless of the level.
What is the protective threshold?
About 0.5 g/L, or 50 mg/dL. Below that level the antiprotease defence in the lung is considered insufficient to restrain neutrophil elastase and the risk of emphysema rises. It is a population-derived figure rather than a sharp biological boundary.
Who should be tested?
Adults with early-onset emphysema, particularly with a basal rather than apical distribution, those with unexplained chronic liver disease or neonatal cholestasis, and relatives of an affected patient. Smokers with deficiency have a far worse natural history.
Related calculators
References
- American Thoracic Society/European Respiratory Society. Standards for the diagnosis and management of individuals with alpha-1 antitrypsin deficiency. Am J Respir Crit Care Med. 2003;168(7):818–900.
- Sandhaus RA, Turino G, Brantly ML, et al. The diagnosis and management of alpha-1 antitrypsin deficiency in the adult. Chronic Obstr Pulm Dis. 2016;3(3):668–682.
Medical Disclaimer: The tools and content provided here are for educational and reference purposes only. They are not intended to substitute for professional medical advice, diagnosis, or treatment. Clinical decisions should always be based on the comprehensive assessment of a qualified healthcare professional.