To avoid loss of inhibiting activity in the sample, we recommend
that urine samples to be used for inhibition analysis
be frozen in small aliquots, because repeated thawing and
freezing may be deleterious to the inhibitory components.
Furthermore, the urine should be frozen as soon as possible
after the collection is completed. It might well be possible to
analyze the inhibitory activity in untimed urine samples,
treated in the same way as the 24-h urine.