Once a device's contact category is determined, one proceeds to the appropriate Level 1 table. In order to maximize hemocompatibility information about the device, one or more tests from each category included in the table should be performed. Several laboratory methods are available for each type of test, and rapid advances in technology in this area are creating more test options. Unfortunately, in the absence of standardized and validated test methods, the requirement for testing across all categories is frequently ignored. Such in vitro test methods are usually quicker and less costly than in vivo methods and do not require the use of animals.
Complement activation is the most relevant immunology test for devices exposed to circulating blood.
An increase in a downstream complement component over baseline levels indicates activation of the complement cascade. Acceptable complement activation limits have not been established, but comparative data are valuable. ASTM F 756, a standardized ASTM hemolysis test method, is available for determining the hemolytic potential of a device or material, and a suggested ISO method may be issued soon. These in vitro tests involve a quantitative measurement of plasma hemoglobin. An increase in plasma hemoglobin correlates with lysis of red blood cells, thereby indicating hemolytic activity of the material exposed to the cells.