Which laboratory test would you use to confirm α1-antitrypsin deficiency in a patient?

To confirm α1-antitrypsin deficiency, serum protein electrophoresis is the appropriate test. This assay separates proteins in the serum based on their size and charge, allowing for the identification of specific protein patterns. In α1-antitrypsin deficiency, there is an abnormal pattern noted on the electrophoresis, specifically a decreased or absent α1 band where α1-antitrypsin typically migrates. This helps in diagnosing the deficiency by quantitatively measuring the levels of α1-antitrypsin, as well as providing insight into any protein abnormalities that may be present in the patient.

The other tests listed do not specifically assess α1-antitrypsin levels or patterns. Serum creatinine primarily evaluates kidney function, while serum bilirubin is used for assessing liver function or hemolysis, neither of which directly provide the necessary information about α1-antitrypsin levels. A 24-hour urine collection is typically used to assess renal function and to measure proteinuria, and is not relevant in diagnosing α1-antitrypsin deficiency. Thus, serum protein electrophoresis is the most specific and informative test for confirming this condition.