Accurate measures of kidney function is important for precision dosing of many medications. The current methods of determining kidney function largely hinge on the use of equations that use common laboratory values such as serum creatinine \& static variables like age \& weight. These are helpful for trending over time, but often are inaccurate during times of medical illness. Other more accurate methods of measuring kidney function include urine collection, although this is not commonly used because of various reasons that make the collection inconvenient or unreliable. The new transdermal glomerular filtration (tGFR) device permits accurate, real-time evaluation of kidney function. This novel method has not been rigorously compared with urine collection \& other methods of determining kidney function in hospitalized patients. The goal of the study is to compare tGFR with other accepted methods of determining kidney function.