MODULE SUPPLEMENT: RENAL SYSTEM
Evaluation of Renal Function

One of the most common measures used to assess renal function is serum creatinine.

Because serum creatinine is not a good measure of renal function, it is prudent, especially when giving drugs, to check creatinine clearance, or at least use one of the formulas, and to check for blood levels of drugs - e.g. peaks and troughs.

Recommend formulas to estimate creatinine clearance:

This is the Cockcroft & Gault formula which uses body weight in Kg; The Lott-Hayton formula uses lean body weight. Some recommend multiplying the formula by .15 (substracting 15%) for women because of their smaller size.

An important caveat: Formulas may get you in the ballpark--but be careful. Data suggest that these formulas can both under and over estimate renal function. Many factors, like diet, can affect creatinine, and these are often overlooked. Yet many elderly individuals may be malnourished, especially in acute care settings or when chronically ill. In addition, the formulas are usually derived from healthy individuals in a steady state--a state that is often not representative of the clients that we often deal with. Use of the C/G equation is especially limited in persons who have been bed bound for more than a week, suffer from a muscle wasting disease, or are taking drugs that "artificially" elevate serum creatinine. The ideal body weight should be used for those individuals who are obese.