Alpha 1-antitrypsin deficiency laboratory findings
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Mazia Fatima, MBBS [2]
Overview
A reduced concentration of serum alpha1-antitrypsin level is diagnostic of AATD. Laboratory findings consistent with the diagnosis of AATD include moderate-to-severe airflow obstruction with an FEV1 in the range of 30-40% of the predicted value, reduced vital capacity, increased lung volumes secondary to air trapping (residual volume >120% of predicted value) are usually present, diffusing capacity values are reduced substantially (<50% of predicted value) in most symptomatic patients. Serum alpha1-antitrypsin levels are determined by nephelometry. Serum testing is used for diagnostic testing in those patients with family histories compatible with the alpha1-antitrypsin deficiency or with siblings with known alpha1-antitrypsin deficiency. In patients with clinical features that are highly suggestive of alpha1-antitrypsin deficiency but whose serum levels are within the reference range the next best step is to perform a functional assay of alpha1 antiprotease, which measures the ability of the patient's serum to inhibit human leukocyte elastase.
Laboratory Findings
A reduced concentration of serum alpha1-antitrypsin level is diagnostic of AATD.[1][2]
Laboratory findings consistent with the diagnosis of AATD include:
- Moderate-to-severe airflow obstruction with an FEV1 in the range of 30-40% of the predicted value
- Reduced vital capacity
- Increased lung volumes secondary to air trapping (residual volume >120% of predicted value) are usually present
- Diffusing capacity values are reduced substantially (<50% of predicted value) in most symptomatic patients
Alpha1-antitrypsin deficiency (AATD) should be considered on the differential diagnosis in any patient who presents with early-onset emphysema or COPD, regardless of their smoking history.
Alphqa1-antitrypsin deficiency (AATD) should be considered in patients with unexplained liver disease at any age, including obstructive jaundice of infancy.
AATD testing should be considered as a laboratory diagnosis and not as a clinical diagnosis.
Serum alpha1-antitrypsin levels
Serum alpha1-antitrypsin levels are determined by nephelometry.
Serum testing is used for diagnostic testing in those patients with family histories compatible with alpha1-antitrypsin deficiency or with siblings with known alpha1-antitrypsin deficiency.
ATS/ERS AAT Deficiency Task Force does not recommend fetal testing or population screening unless:
- Prevalence of AATD is high (>1 case per 1500 population)
- Smoking is prevalent
- Adequate counseling services are available
Serum alpha1-antitrypsin levels has a normal reference range of 100-300 mg/dL. Serum alpha1-antitrypsin levels less than 80 mg/dL suggest a risk for lung disease.
Serum alpha1-antitrypsin level alone has a low sensitivity for detecting alpha-1-antitrypsin deficiency. 80 mg/mL of serum alpha1-antitrypsin represents the threshold level.
Emphysema is common below the threshold level.
Functional assay of alpha1-antiprotease
In patients with clinical features that are highly suggestive of alpha1-antitrypsin deficiency but whose serum levels are within the reference range the next best step is to perform assessment of function of alpha1 antiprotease, to measure the ability of the patient's serum to inhibit human leukocyte elastase.
Perform liver function tests in patients with low or borderline levels of alpha1-antitrypsin.
Additional tests include measurement of:
- Serum transaminases
- Bilirubin
- Albumin
- Routine clotting function
- Activated partial thromboplastin time
- International normalized ratio.
References
- ↑ Parr DG, Sevenoaks M, Deng C, Stoel BC, Stockley RA (2008). "Detection of emphysema progression in alpha 1-antitrypsin deficiency using CT densitometry; methodological advances". Respir. Res. 9: 21. doi:10.1186/1465-9921-9-21. PMC 2287169. PMID 18271964.
- ↑ Greene DN, Elliott-Jelf MC, Straseski JA, Grenache DG (2013). "Facilitating the laboratory diagnosis of α1-antitrypsin deficiency". Am. J. Clin. Pathol. 139 (2): 184–91. doi:10.1309/AJCP6XBK8ULZXWFP. PMID 23355203.