The assay recovery in kidney disease urine wasevaluated usinga high spike of a known concentration of the target synthetic peptidein two separate preparations consisting of a pool of FSGS samplesof a high (10 mg/mL) or low (1 mg/mL) total protein concentration.Recovery ranged from 99% to 121% for nephrin, 106% to 114% for podocalyxin,and 98% to 123% for podocin (Table S6). Here, NPHS2 is linked to kidney disorder.