Wis. Stat. § 632.50
If under the rules of any insurer issuing life insurance, its medical examiner has authority to issue a certificate of health, or to declare the proposed insured acceptable for insurance, and so reports to the insurer or its agent, the insurer is estopped to set up in defense of an action on the policy issued thereon that the proposed insured was not in the condition of health required by the policy at the time of issue or delivery, or that there was a preexisting condition not noted in the certificate or report, unless the certificate or report was procured through the fraudulent misrepresentation or nondisclosure by the applicant or proposed insured.
Wis. Stat. § 632.50
Estoppel under this section may apply against insurers who seek a medical examiner's opinion regarding fitness for insurance without establishing any formal rules regarding the examiner's authority. Grosse v. Protective Life Insurance Co. 182 Wis. 2d 97, 513 N.W.2d 592 (1994).