Thank you for your effort in comparing all these calculators. I agree with you about the importance of determining which body weight you have to use. However,in you example you used an extremely old man which result in the following: *It is well-known that geriatrics have a very low muscle mass even if they are obese which ideally means you have to use their ideal body weights or their actual body weigh (if they are underweight ) in the cleatinine calculations and NOT to use their actual (if they are not obese)or adjusted to prevent any over estimation of their renal function.
*Knowing that they have low muscle mass is very important specially for female geriatrics for this culculation. * Knowing if the geriatric patient is diabetic will cause you to expect a further over estimation in your calculations for example if you calculate it to be 50 ml/hr and he is diabetic and your are dosing an antibiotic like vancomycin or an aminoglycoside …will prevent you from large increases in the doses…be cautious in your increment
*Because almost always with diabetes there is an underlined kidney disease that will not be detected by creatinine calculations but it has to be measured by 24hr collection. This is last statement is from a webinar of a nephrologist who spoke about the impact of DM on kidney function…. and also from my experience in dosing antibiotics in diabetic patients… I always remove 10 ml/hr from what I got from the calculation in diabetic patients if I got 50 ml/hr ,I do my dose calculations as if it is 40 ml/hr and if works fine with me and I hit the right dose from the first time.
* Another thing a lot of hospital lab softwares show the GFR and a lot of doctors count on it but actually in my experience it overestimate the renal function in geriatrics. *Geriatrics means elderly above 70 but you can consider geriatrics anyone above 65 years old …I am saying so because I consider all the co-morbidities that always available at this age like DM, Heart Failure, Hepatic Failure, CKD..which all impact the actual renal function. All these cause the patients to die around the age of 65.