OBJECTIVE: To validate and develop an immunonephelometric assay for the determination of
alpha-1 antitrypsin (AAT) levels in dried blood spots from COPD patients in
Brazil. METHODS: We determined AAT levels in serum samples and dried blood spots from 192 COPD
patients. For the preparation of dried blood spots, a disk (diameter, 6 mm) was
placed into a tube, eluted with 200 µL of PBS, and stored overnight at 4ºC. All of
the samples were analyzed by immunonephelometry in duplicate. We used the
bootstrap resampling method in order to determine a cut-off point for AAT levels
in dried blood spots. RESULTS: The correlation coefficient between the AAT levels in serum samples and those in
dried blood spots was r = 0.45. For dried blood spots, the cut-off value was 2.02
mg/dL (97% CI: 1.45-2.64 mg/dL), with a sensitivity, specificity, positive
predictive value, and negative predictive value of 100%, 95.7%, 27.2%, and 100%,
respectively. CONCLUSIONS: This method for the determination of AAT levels in dried blood spots appears to
be a reliable screening tool for patients with AAT deficiency.