Calculation of 51Cr-EDTA clearance in children from the activity in one plasma sample by transformation of the biexponential plasma time-activity curve into a monoexponential with identical integral area below the time-activity curve.

The relation between 51Cr-EDTA clearance and plasma 51Cr-activity in children was analysed introducing the functions s(t) and g(t) for transformation of the biexponential plasma time-activity curve to a monoexponential with identical area below the time-activity curve. The theory of s(t) and g(t) were discussed and the variation of g(t) with time was determined empirically. The functions s(t) and g(t) were used to derive a formula for the calculation of 51Cr-EDTA clearance in children from one single plasma sample (ClST) withdrawn between 90 and 150 min after the injection. ClST and 51Cr-EDTA clearance calculated by means of a standard method were almost identical (r = 0.991). It is concluded that the formula may prove useful for calculation of 51Cr-EDTA clearance in children.