has changed since last episode is used to compare the latest sample with the second-last sample, whether or not these samples are blank.
We can also use the expression has not changed since last episode.
For example, given the following case fragment,
01 Jun 03 20 Jun 03 30 Jun 03 15 Oct 03 02 Nov 03 ReqDr Jones Jones Jones JONES Jones CopyDr Smith Smith Brown Smith Tests Lipids Lipids Lipids Insurance DVA DVA DVA
ReqDr has not changed since last episode
CopyDr has changed since last episode
Tests has changed since last episode
Insurance has not changed since last episode