With the rapid, routine method we describe, 24-h urine is
diluted to contain a fixed concentration of creatinine (5
mmol/L), because it has previously been demonstrated (9,16)
that inhibiting activity and urinary creatinine are correlated.
Correcting for this correlation also makes it easier to compare
the inhibition index with other information on urine composition
(3) and with the inhibitory activity as measured on other
occasions in urines of various native concentrations.