can a previous employer in the state of washington tell a prospective employer about an employee's on the job injury claims?

Generally, private health care information is supposed to be kept confidential by medical providers, employers, and others absent a signed release authorization. The mere existence of prior L&I claims, however, may be discovered through public sources. Whether a past employer improperly released confidential health care information can be difficult to prove without confirmation by the recipient. You should get a copy of your entire personnel file from prior employer. Its always good to know exactly what is in your file and sometimes there are notations showing who checked up on you and what information was released.