Abstract: Systems and methods are provided for monitoring a immunosuppressant drug level and renal function, hepatic function, or a combination thereof in a patient, comprising obtaining a small volume blood sample from the patient; determining the level of at least one immunosuppressant drug in the small volume blood sample and determining the level of a second immunosuppressant drug or analyzing the renal function, the hepatic function, or a combination thereof in the patient. In some embodiments, the immunosuppressant drug levels are determined using a liquid chromatography tandem mass spectrometry (LC-MS/MS) procedure. Also provided are kits for use in any of the systems and methods described herein.