**Abstract**

Since the introduction of the most expensive drug in the world (Eculizumab) in the therapeutic arsenal of many diseases involving the alternative complement pathway (ACP) in their pathophysiology, the unmet need to perform simple ACP assays affordable for all countries has become one of the major challenges of the contemporary medicine. The assay currently used is AH50, despite it still challenging for several laboratories. This educational chapter consists on a detail protocol of standardized hemolytic assay AP100 and aims to help clinical laboratories over the world and especially those of the developing and low incomes countries to perform it. The procedure is essentially the same as for the timed lysis assay and dilution methods (AP50) except the concentration of ACP buffer and the chicken erythrocyte density used to make the gels. In clinical field, AP100 has at least nine applications in disease diagnosis and follow-up. AP100 has many advantages over the AH50 as it is more reliable for the Eculizumab monitoring and more practical with a purpose to be stored and transported for several weeks. AP100 is a portable and easy to use device both at the bedside and in the companion medical care.

**Keywords:** alternative complement pathway, AP100, medicine, simple assay, low income countries
