Free · Dialysis measurements

Dialysis Urea Reduction Percentage

Compute the percentage decrease in urea from paired pre-dialysis and post-dialysis concentrations with consistent urea mass and molar units.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Health results are educational estimates, not a diagnosis or treatment recommendation. A qualified clinician can interpret measurements in the context of your health.

Formula and method

Urea falls from 50 to 15 mg/dL: the decrease is 35/50, or 70%.

URR (%) = 100 × (pre − post) / pre.

Worked example

Enter these known values and leave the other values blank.

Pre-dialysis urea (whole molecule)
50 mg/dL
Post-dialysis urea (whole molecule)
15 mg/dL
Urea reduction percentage
70 %

Assumptions and limitations

  • Both concentration controls represent the whole urea molecule. With molar mass 60.056 g/mol, 1 mmol/L = 6.0056 mg/dL and 1 g/L = 100 mg/dL. Do not enter a BUN mass measurement in one control and whole-urea mass in the other. Paired BUN measurements in identical units yield the same numerical ratio, but their mass-to-molar conversion differs.
  • Use a positive pre-dialysis concentration and a nonnegative post concentration at most the pre value. A 100% reduction with post zero is valid in the forward direction; a post-zero inverse cannot uniquely recover pre from a 100% reduction.
  • The NIDDK 65% benchmark is historical conventional-hemodialysis context, not a guarantee of adequate dialysis or a recommendation for different schedules. Follow clinic sampling protocols.

Common questions

Can the two controls use different units?

Yes, provided both measure whole-molecule urea. Unit conversions run locally and use the stated molar mass. Do not mix whole-urea and urea-nitrogen mass values.

Does 70% prove dialysis was adequate?

No. The historical numerical benchmark is only one assessment; sampling, schedule, repeated results and clinical context matter.

References

Correct urea g/L to 100 mg/dL and urea mmol/L to 6.0056 mg/dL using the stated 60.056 g/mol urea molar-mass convention; the source mixed a urea-nitrogen factor into urea mass units. Require nonnegative post-dialysis urea.

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