Alpha-1 Antitrypsin Level and Genotype

What the result means

Deficiency

A serum level below 100 mg/dL, or below 20 micromol/L.

Protective threshold

57 mg/dL, or 11 micromol/L. The classical figure - and it has been REFUTED as a predictor of COPD risk.

What replaced it

Genotype. PI*ZZ and rare ZZ-equivalents are independently associated with COPD; no data show a risk that turns on the level threshold.

Both directions

A level above the threshold is not reassurance, and a level below it is not a risk estimate.

PI*MZ

A carrier state with a modest risk amplified by smoking. Not equivalent to ZZ, and not to be reported as though it were.

Units

Not interconverted. The published pairs of 57 with 11 and 100 with 20 imply different factors and are conventional, so each unit uses its own thresholds.

Who to test

Every adult with COPD, emphysema, incompletely reversible asthma or unexplained liver disease, and siblings of anyone with the deficiency.

Method matters

Nephelometry and radial immunodiffusion do not return the same value for the same sample. Compare against the reporting laboratory reference range.