Agglutination activity is expressed in μg/mL and is determined from serial dilutions of a 1 mg/mL solution. This activity is the lowest concentration to agglutinate a 2% suspension of human erythrocytes in phosphate buffered saline, pH 6.8, after 1 hr incubation at 25 °C.

PHA consists of two molecular species, an erythroagglutinin (PHA-E) which has low mitogenic activity and high erythroagglutinin activity, and leucoagglutinin (PHA-L) which has high mitogenic and leucoagglutinating activity, but very low erythroagglutinating activity.^1,2
PHA-E is not blood group specific, but agglutination can be inhibited by certain oligosaccharides.³ PHA-P is the protein form of PHA prior to separation and purification of erythroagglutinin and leucoagglutinin.⁴ PHA-M is the mucoprotein form.⁴ Conjugates are prepared from the corresponding purified lectins.