It is true that fat weight does not contribute to uremic state and both DOQI and uptodate recommend using ideal rather than actual body weight for determination of weekly KT/V. However, there are some people who are overweight but also have big muscles and not all their excess weight is fat. My own belief is an adjusted body weight similar to what is used in TPN calculations should be used for these patients. I would like Dr. Oreoupoulos to comment on this issue. What is the position of ISPD on this issue?

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ali s, Doctor/MD from CA asked
It is true that fat weight does not contribute to uremic state and both DOQI and uptodate recommend using ideal rather than actual body weight for determination of weekly KT/V. However, there are some people who are overweight but also have big muscles and not all their excess weight is fat. My own belief is an adjusted body weight similar to what is used in TPN calculations should be used for these patients. I would like Dr. Oreoupoulos to comment on this issue. What is the position of ISPD on this issue?

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Thank you for asking my opinion that I will be quite happy to offer but I do not think that this is necessarily the position of the ISPD on this issue.

My answer will have to aspects A) a theoretical one and B) a practical one.

Theoretical Answer:

When one calculates the Kt/V the V reflects the body water which usually is expressed as a percentage of body weight.

Since the fat issue does not contain water, one would expect that in obese patients calculations of V as a percentage of body weight would give a false higher value and therefore a false lower Kt/V.

If on the other hand the person is muscular, indeed the calculation of the V as a percentage of body weight would be accurate in these patients.

The adjusted body weight (ABW) (( adjusted body weight = ideal body weight + 0.4 (actual body weight – ideal body weight)) assumes that the difference in body weight from ideal is 40% that gives an average value.

I don’t believe there is any study that has verified that the use of the ABW instead of the Ideal Body weight ( IBW) in patients on peritoneal dialysis for the estimation of Kt/V and its value . In 2008 Dr. Piraino’s group (American Journal of Kidney Disease Vol. 52 1122-30) tried to correlate the association of Kt/V and creatinine clearance with outcomes in anuric dialysis patients and they found that if one uses the actual body weight, there is a good correlation between mortality and Kt/V

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