On written request of the claimant, an insurer that denies a claim made on an individual health insurance policy shall give written notice to the claimant that states fully the reason for the denial. The reason given by an insurer for denial of a claim shall not act as an estoppel or limit the insurer from offering an additional reason for the denial. The notice given by an insurer under this section is subject to 45 C.F.R. § 164.522(b).