You don’t have to be retested unless you need documentation for specific accommodations. If that is the case, there may be different criteria for how current the documentation is depending on who you are requesting the accommodations from.
High-stakes testing agencies usually require LD documentation to be current within the past 5 years. Many employers may not be concerned about how current the documentation is. Large companies would probably adhere to the 5-year rule; small companies may not.
Learning disabilities evaluations can be pretty expensive – usually running anywhere from $800 – $1500. So you might want to consider whether or not you actually need the diagnosis or if you’re just curious. If you need the documentation to request accommodations at work or on a standardized test, then you might want to explore getting a diagnosis. If you have a community mental health center nearby, they sometimes do LD evaluations on a sliding scale, which can cut your cost dramatically. Likewise, some colleges with graduate psychology departments may also provide LD evaluations on a sliding scale. If you are unemployed or looking for a better job, you should contact your local Rehabilitation Services Agency (http://rsa.ed.gov/people.cfm, click on “State Agencies/Contacts”).