Presumably, the large size (1 kb and larger) urine DNA
is derived from cells shed into the urine from the urinary
tract. Consistent with this hypothesis is the fact that the
large size class of DNA can be reduced in abundance by
low-speed centrifugation before electrophoresis, in which
cells are sedimented, and small size class of DNA can
only be recovered from the supernatant of urine. It was
noted that the amount of this large class of urine DNA
varied significantly from sample to sample, even from the
same subject, as seen in Figure 1, B-D.