PURPOSE: In Europe and North America a percentage of patients presenting with emphysema have a genetic disorder resulting in suboptimal serum concentrations of AAT. For several reasons, including the complexity of current laboratory methods for analysis and measurement of this acute phase protein, relatively few patients with this condition are correctly diagnosed. We have set out to develop a simple, rapid, test for screening patients with low serum levels of AAT and therefore at risk for AAT deficiency. This quick test requires no special equipment and can give a result during a physician office visit, thereby identifying patients who require full diagnostic testing.
METHODS: The test as developed employs a drop of blood from a fingerstick. The AAT in the sample reacts with antibody coated gold nanoparticles in the device and the complex is captured by another AAT specific antibody which is immobilized on the reaction membrane. The target sensitivity of this test was set at 1mg/ml (20μM), which is higher than the level used to determine severe AAT deficiency (11μM). At the cut off and all higher concentrations the test gives a visible red line. The sensitivity was determined using calibrated plasma from deficient patients to which were added varying concentrations of purified AAT.
RESULTS: Using this method we were able to establish an assay which gave a negative result with a plasma sample containing 0.68mg/ml and a positive result with 1.0mg/ml AAT. Specificity was demonstrated by inhibition studies using purified anti-AAT antibodies.
CONCLUSION: This rapid, lateral flow assay enables a discrimination to be made between patients with normal and abnormally low concentrations of circulating AAT.
CLINICAL IMPLICATIONS: In addition to the cut off selected; the speed, the simplicity and the fact that it requires one drop of blood should increase the frequency of screening and improve the patient identification rate for the estimated 200,000 patients with AAT-associated emphysema the vast majority of whom remain unidentified.
DISCLOSURE: Jim Carney, Employee Todd Willis and Amy McGrath are employees of Talecris Biotherapeutics.