Simple method for α1-antitryspsin deficiency screening by use of dried blood spot specimens

Abstract

The use of dried blood spot (DBS) specimens in quantitative α1-antitrypsin (α1-AT) detection or genetic analysis is limited because protein levels in the samples are low and they contain components that can interfere with polymerase chain reaction amplification. A methodological adaptation was developed to overcome these drawbacks which is discussed here. The study population consisted of 200 healthy volunteers and 300 patients with chronic obstructive pulmonary disease (COPD). DBS specimens were tested for α1-AT concentration using a modified nephelometric assay and phenotyped with an isoelectric focusing method. Genetic diagnosis was established by deoxyribonucleic acid sequencing using a simple purification procedure to remove contaminants. The nephelometric method showed a detection limit of 0.284 mg · dL-1, corresponding to a serum concentration of 13 mg · dL-1. The correlation coefficient between α1-AT concentrations in DBS versus serum samples was R2=0.8674 (p<0.0001). All 200 healthy individuals had DBS α1-AT concentrations >1.9 mg · dL-1, corresponding to 114 mg · dL-1 in serum samples. One hundred and twenty-five COPD patients (42%) showed α1-AT values <1.8 mg · dL-1. Twenty patients with the PIZ phenotype had α1AT values lower than 0.64 mg · dL-1. On the basis of genotyping, one COPD patient was classified as heterozygous (PIMMheerlen). Selective elution of contaminants resulted in optimal α11-antitrypsin genotyping. Because of its sensitivity and excellent correlation with the standard method, the dried blood spot quantitative assay is a reliable tool for routine measurement of α1-antitrypsin. (C) ERS Journals Ltd 2000.