relationship), race (10% higher in African Americans), and diabetes (lowered value); therefore, test results need to be adjusted for these variables. It has been found that reporting AFP in multiples of the median (MoM) leads to good correlation with infant risk. MoM is calculated by dividing the patient's AFP value by the median reference value for that gestational age. Most screening programs use 2.0 MoM as the upper limit and 0.5 MoM as the lower limit for maternal serum AFP.
α1-Acid Glycoprotein (Orosomucoid).
α1-Acid glycoprotein comprises five carbohydrate units attached to a polypeptide chain. Owing to its low pI (2.7), it is negatively charged even in acid solutions, a fact that led to its name. Sequences of haptoglobin, immunoglobulins, and a,-acid glycoprotein show considerable homology, leading to speculation that these proteins share a precursor in the evolutionary past. α1-Acid glycoprotein is implicated in the formation of certain membranes and fibers in association with collagen and may inactivate basic hormones such as progesterone.
α1-Antichymotrypsin. α1-Antichymotrypsin (α1-ACT) is a serine proteinase with cathepsin G , as pancreatic elastase, cell chymase, and chymotrypsin mast
targetenzymes. α1-ACT carries four oligosaccharide side chains. It migrates between the α1 and α 2 zones on high resolution serum protein electrophoresis.
Inter- α-trypsin Inhibitor. Inter-α-trypsin (ITI) inhibitor comprises at least three distinct polypeptide subunits: two heavy chains designated H, and H2 and a light chain designated L or bikunin. The light chain is responsible for the inhibition of the proteases trypsin, plasmin, and chymotrypsin. On high- resolution serum electrophoresis, ITI migrates in the zone between the α1 and α 2 fractions.
Gc-globulin (Group-Specific Component; Vitamin D-Binding Protein). Gc-globulin is another protein that migrates in the α1- α 2 interzone. This protein exhibits a high binding affinity for Vitamin D compounds and actin, the major constituent of the thin filaments of muscle. Due to genetic polymorphism, several phenotypes of Gc-globulin exist.