Hallberg P., Melhus H., Hansson L.-O., and Larsson A. “Cystatin C Vs Creatinine As Markers of Renal Function in Patients on Digoxin Treatment”. Upsala Journal of Medical Sciences, vol. 109, no. 3, July 2009, pp. 247–254, doi:10.3109/2000-1967-087.