Apolipoprotein A-I (apo A-I) is a protein that has specific roles in the transportation and metabolism of lipids and is the main protein component in high-density lipoprotein. This test measures the amount of apo A-I in the blood. Apo A1 recommends to patients with personal or family history of high lipids, to check the cause of their high lipid is due to deficiency of Apo A1. This test can be performed in Serum/heparinized or EDTA plasma.