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 |
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.
