One Illinois judge has served up a warning to future whistleblowers who might bring claims against skilled nursing facilities.

The case in question involves a former corporate nurse at Arlington Rehabilitation & Living Center, in Long Grove, IL. He alleged that his former employer — along with two other SNFs, and a therapy provider — systematically upcoded Medicare patients, according to Bloomberg Law.

Experts are presenting data to support those claims, but presiding Judge Elaine Bucklo is questioning whether broad trends and damages can be drawn from such data, without accounting for individual patient conditions. She has granted motions to exclude part of the expert witness testimony in the case, given defendants’ concerns.

Some observers believe the U.S. District Court’s decision is part of a trend of putting more pressure on whistleblowers to show individual examples of fraudulent activity, instead of making broad determinations on small statistical samples. A single expert will be allowed to present testimony on CMS’ claims review processes and criteria to establish medical necessity, but he is specifically restricted from testifying as to whether the SNFs’ conduct was fraudulent.

“This decision shows the pitfalls of divorcing a medical necessity False Claims Act case from the actual medical decision-making for individual patients,” Brad Robertson, a partner at Bradley Arant Boult Cummings in Birmingham, AL, told Bloomberg. “Both of the experts offered opinions about whether care was fraudulent without doing any kind of sufficient review or analysis of the care provided to the individual patients in question. Defendants should keep an eye out for these kinds of shortcuts and mistakes in expert methodology.”

Experts cited in the report said that showing a large sample of individual cases to prove medical necessity could be challenging for other whistleblowers in the future.