An accurate estimate of volume of distribution of urea (UDV) is critically important to guide the prescription of therapy and for the quantification of delivered dialysis dose in patients.

Total body water (TBW) is substantially the same as UDV in most patient populations.

The Watson equations are used to estimate UDV or TBW, and are also known as anthropometric equations.

The formulas used in this tool are:

• UDV Females = -2.097+ (0.1069*Ht) + (0.2466*Wt)
• UDV Males = 2.447 - (0.09516*Age) + (0.1074*Ht) + (0.3362*Wt)
• Ht = Height in centimeters
• Wt = Weight in kilograms
• Age = Age in years

Note:

• Patients with acute renal failure have a substantially higher UDV than this formula will predict (Himmelfarb, et al)
• Patients on chronic hemodialysis often have a substantially lower UDV than this formula will predict (Kloppenburg, et al)

References:

• Bland JM, Altman DG. Statistical methods for assessing agreement between two methods of clinical measurement. Lancet. 1986;1(8476):307-10.
• Himmelfarb J, Evanson J, Hakim RM, et al. Urea volume of distribution exceeds total body water in patients with acute renal failure. Kidney Int. 2002;61(1):317-23.
• Kloppenburg WD, Stegeman CA, De jong PE, et al. Anthropometry-based equations overestimate the urea distribution volume in hemodialysis patients. Kidney Int. 2001;59(3):1165-74.
• Watson PE, Watson ID, Batt RD. Total body water volumes for adult males and females estimated from simple anthropometric measurements. Am J Clin Nutr. 1980;33(1):27-39.