Response to the letter about 'Development of a modified sampling and calculation method for isotope plasma clearance assessment of glomerular filtration rate in patients with cirrhosis and ascites'.

However, the design of the study is surprising. As mentioned by the guidelines, the only accepted method in this type of patients is the comparison between urine and plasma samples, because one avoids the problems of additional spaces of distribution. The authors claim that this method is inaccurate, although many others such as Bröchner-Mortensen J., Chantler C., Klassen D.K., and Otto A.C. have used this method as the reference for testing simplified methods. However, I do not deny the technical difficulties related to the method, such as the need for multiple long periods of urine collection.