Reliability of haemodialysis urea kinetic modelling in children

The reliability of urea kinetic modelling (UKM) in paediatric haemodialysis was tested by comparing results of the classic variable volume model (UKM3), a recently introduced two-sample modification of this (UKM2) and direct quantification by a partial dialysate collection method (PDC). Urea generation rate (G) was also found from a 1-week collection of dialysate and urine (OWC). Nine children aged 2-18 years and weighing 10.6-39.9 kg were examined over 1 week (25 treatments). UKM3 and UKM2 gave almost identical results, but deviated from PDC and OWC. The two indirect methods overestimated G by 24% and 18%. However, the correlations between the results were very high for all variables and all methods (r > or = 0.96). Repeating UKM3 and UKM2 mid-week for 5 consecutive weeks, the following coefficients of variation were found: for the normalised whole body urea clearance (Kt/V) 10% and 11%, respectively; for normalised protein catabolic rate 17% and 14%. It is concluded that all tested methods can be used, but each method requires its own reference interval. Results of UKM seem to vary somewhat more than in adults. This should be considered when assessing children by such methods.