A method and kit for identifying the presence of an early biomarker of impaired renal status following a renal event in a mammalian subject. The method typically comprises (a) providing a body fluid sample obtained from a mammalian subject following a renal event; and (b) detecting in the provided sample the presence of a protein selected from the group consisting of aprotinin, alpha-1-microglobulin (A1M), alpha-1-acid-glycoprotein (A1AG), microalbumin, and combinations thereof, the presence thereof serving as an early biomarker of a change in renal status. The method can include a kit for point-of-care detection of the early biomarker of impaired renal status. Identification of the presence or absence of the early biomarker typically directs a caregiver's therapeutic decision regarding managing treatment of the subject for impaired renal status. The invention also includes a method of assessing the administration of aprotinin during cardiopulmonary bypass surgery and provides for methods where the level of aprotinin in the subject's urine directs a caregiver's therapeutic decision regarding the intra-operative administration of aprotinin.