This is an update of a previous post on this site dated June 8, 2016, entitled "The Recovery of Medical Expenses in Personal Injury Cases - Is the Traditional Rule About to Change?" We now have the answer: no.
On November 17, 2017, in Dedmon v. Steelman, No. W2015-01462-SC-R11-CV, the Tennessee Supreme Court decided a "hot" issue regarding recoverable medical expenses in Tennessee personal injury cases: the plaintiff continues to be able to prove, through expert medical testimony, the original, undiscounted amount of the charges, and the defense cannot introduce evidence of what was accepted from collateral sources such as insurance companies. The defense can attempt to prove a different "reasonable" value than the original, undiscounted charges, but not based on what was accepted by the medical providers from insurance companies--that figure appears to be off limits since it runs afoul of the collateral source rule (even if the word "insurance" is not mentioned).
For example, if the original, undiscounted medical expenses attributable to an accident are $100,000 but a health insurance carrier only paid $20,000 and most or all of the remaining balance was written off by the medical providers, and if a qualified expert testifies that $100,000 is reasonable in amount, was necessary to treat the plaintiff, and that the need for the treatment was caused by the accident, then the plaintiff can introduce the higher amount into evidence at a trial, meaning the jury can hear and consider this amount ($100,000 in this example). The defense cannot introduce the $20,000 paid by insurance and accepted by the medical providers in full satisfaction of the charges. The defense can attempt to question the "reasonableness" of the $100,000 on other grounds. The defense can also question whether the treatment was "necessary" and/or whether it was caused by the accident (the latter being a common battleground when it comes to medical expenses).
At this moment, the Dedmon decision is probably the most up-to-date written piece on the law across the nation on this issue. Whether the Tennessee legislature attempts to modify or change the result in this case remains to be seen.