Screening and Diagnosis
Testing for AAT deficiency begins with a simple blood test – an immunoassay – to determine the concentration of AAT protein in plasma or serum.
Blood tests will reveal three types of patients:
| Level in milligrams per deciliter (mg/dL) | Level in micromolar units (µM) | |||
|---|---|---|---|---|
| Normal | ≥150 mg/dL | ≥20 µM | ||
| Borderline Normal | 90 – 140 mg/dL | 12 – 19 µM | ||
| Deficient | <80* mg/dL | <11* µM |
*Historical level
Patients who are deficient or borderline should undergo a second blood test – phenotyping – to confirm the genetic abnormality that causes AAT deficiency.1
Phenotyping for AAT deficiency is complicated, with more than 90 different gene mutations (alleles) identified. The most common alleles are M (normal), and S, Z, and null (deficient). 1 The chart below shows how to evaluate the results of phenotyping.
| (Measured by Radial Immunodiffusion) | Normal Range | Deficient Range | ||
|---|---|---|---|---|
| Units: mg/dL | 150 – 350 | <80* | ||
| Units: µM | 20 – 48 | <11 | ||
| *Or less than 50 mg/dL if measured by laboratories using nephelometry instead of radial immunodiffusion | ||||
References
- American Thoracic Society /European Respiratory Society Statement: Standards for the diagnosis and management of individuals with alpha-1 antitrypsin deficiency. Am J Respir Crit Care Med. 2003; 168:818-900.
