calculating creatinine clearance in elderly patients

by Sherri
(Raleigh,NC)

Patient is 82 yr old male weighing 188 lb and having a serum creatinine of 1.8 mg/dL So far I've converted 188 lb to kg which is 85kg.I don't understand the example of formula in book which is for 68 yr female 160 lb and creatinine of 1.8mg/dL They converted her weight to kg which is 72.73 kg then they have formula as follows CrCl=0.85x (140-68 yr)x 72.73 kg/ 72 x 1.8 mg/dL.What is 0.85 for and 140-68 yr for?