OPINION
This worker’s compensation case is before this court for the second time, after an extensive history of proceedings. Treating the present appeal as a petition for review, see
City and Borough of Juneau v. Thibodeau,
William S. Smallwood first filed a claim for worker’s compensation in October of
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1973, alleging that his employment as a truckdriver with Burgess Construction Company contributed to the acute renal failure he suffered in 1970, necessitating the surgical removal of both kidneys. At the first hearing before the Worker’s Compensation Board on June 4, 1974, Burgess objected to Smallwood’s introduction of medical reports absent an opportunity to cross-examine the physicians who made the reports. Although the medical reports were admitted, the Board expressly disavowed any consideration of, or reliance on, them in reaching the decision to award compensation to Smallwood. The matter was appealed to the superior court, which held that Burgess had waived its right to cross-examine Smallwood’s physicians and ordered the case remanded to the Board for reconsideration on the basis of all the evidence, including the medical reports.
2
In
Commercial Union Cos. v. Smallwood,
Smallwood worked as a truckdriver for Burgess from 1964 until his hospitalization for acute renal failure in July, 1970. That Smallwood had a history of renal dysfunction, beginning years before his employment with Burgess, is without dispute. Smallwood’s claim before the Board was based on his theory that hypertension, exacerbated by his working conditions, aggravated his pre-existing kidney condition to produce acute renal failure.
On remand, the Board relied on testimony from the previous hearing and the depositions of Dr. Henry Tenckhoff and Dr. William Bennett. Dr. Tenckhoff, a kidney specialist who examined Smallwood after his kidney failure, testified that in his opinion Smallwood’s kidney failure was caused by malignant hypertension. Hypertension can be controlled with proper medical treatment and a low salt diet. Smallwood’s medical records indicate there has been a noticeable rise in his blood pressure since 1968, developing into malignant hypertension by 1970. Dr. Tenckhoff was of the opinion that Smallwood’s working conditions accelerated his hypertension since he had little opportunity to see a physician or maintain the proper diet while on the road. Thus, he concluded that “working conditions played a significant role in Mr. Small-wood’s hypertension and therefore in his renal disease.”
The defendant’s medical expert, Dr. Bennett, also a kidney specialist, believed that Smallwood’s acute kidney failure resulted from a natural progression of his preexisting condition, which was “probably” not aggravated or accelerated by his employment conditions.
The Board issued its decision and order denying Smallwood compensation on November 1, 1977. Following a fairly extensive review of the evidence, the Board found that “[njeither Dr. Tenckhoff nor Dr. Bennett can say to a reasonable degree of medical probability that applicant’s kidney failure was caused by his employment,” and concluded that Smallwood’s kidney failure was not related to his employment but was “the natural progression of a disease which he has had for many years.” Smallwood appealed this decision to the superior court which reversed and remanded for a determination of the extent of Smallwood’s disability. The superior court determined that the Board failed to apply the statutory presumption of coverage and improperly placed the burden on Smallwood to establish that his disability was work related. Applying the correct standard and presumption, the court itself independently analyzed the evidence before the Board and concluded that there was no substantial evidence to overcome the presumption of coverage. Burgess appeals from this decision.
We agree with the superior court’s legal conclusion that the Board applied an incorrect standard in denying compensation to Smallwood, but find that the court erred in *315 independently evaluating the evidence and reaching its own conclusion of compensability. Thus, we remand to the Board once again for reconsideration.
It is well established in worker’s compensation law
“that a preexisting disease or infirmity does not disqualify a claim under the work-connection requirement if the employment aggravated, accelerated, or combined with the disease or infirmity to produce the death or disability for which compensation is sought.”
Thornton v. Alaska Workmen’s Compensation Board,
Nowhere in the Board’s findings and conclusions is there any mention of the statutory presumption of coverage, or of aggravation or acceleration of a pre-existing condition. The language employed by the Board in its decision suggests that it improperly placed the burden of establishing work-relatedness on Smallwood. Rather than concluding that there was substantial evidence that Smallwood’s kidney condition was not aggravated or accelerated by his employment, the Board concluded that it was “unable to find that applicant’s kidney failure was related to his employment for the defendants.” (emphasis added).
Burgess maintains that the statutory presumption of coverage contained in AS 23.30.120(1) is not applicable in this case, and thus the Board properly placed the burden on Smallwood to establish through medical analysis that his disability was work-related. Burgess contends that this conclusion is mandated by the following language in our prior decision in this case.
“The claim in this case is based on highly technical medical considerations pertaining to the cause of the claimant’s renal failure. While valid awards can stand in the absence of definite medical diagnosis, this would appear to be the type of case in which it is impossible to form a judgment on the relation of the employment to the disability without medical analysis.”
Commercial Union Cos.
v.
Smallwood,
Moreover, the language in
Small-wood
emphasized by Burgess must be taken in the context of our holding that remand to the Board should include the right of Burgess to cross-examine Smallwood’s medical witnesses and “the right of either party to adduce additional medical evidence.”
Burgess also argues against application of the presumption in cases where the injury is not shown to have occurred on the job and is not sudden or unexplained, but rather the result of a pre-existing condition which may have been aggravated by the employment. There is nothing in AS 23.30.-120(1) which limits its scope in the manner urged by Burgess. The presumption of compensability found in AS 23.30.120(1) is expressly made applicable to any “proceeding for the enforcement of a claim for compensation under this chapter” of the Worker’s Compensation Act. The broad inclusiveness of this language does not mean that the mere filing of a claim gives rise to the presumption of coverage, for, as was previously indicated, there must be some evidence that the claim arose out of, or in the course of, employment before the presumption arises. We have repeatedly applied the presumption in AS 23.30.120(1) to claims of aggravation or acceleration of a pre-existing condition 6 and see no reason to *317 change that rule now. Therefore, we conclude that the Board erred in failing to apply the presumption that Smallwood’s claim was compensable in the absence of substantial evidence that his disability was not aggravated or accelerated by his employment.
In addition to denying Smallwood the proper presumption of coverage, the Board appears to have applied an incorrect test of causation. The Board found that “[njeither Dr. Tenckhoff nor Dr. Bennett can say to a reasonable degree of medical probability that applicant’s kidney failure was caused by his employment.” We stated in
Ketchikan Gateway Borough v. Saling,
We cannot, however, affirm the superior court’s reversal of the Board’s order denying compensation on the ground that there is an absence of substantial evidence to overcome the presumption any more than we can uphold the Board’s order on a finding of substantial evidence to support its decision that Smallwood’s injury is not compensable. It is well established that the question of whether employment aggravated or accelerated a pre-existing disease or injury is one of fact to be determined by the Board and it is not the function of the court to reweigh the evidence or choose between competing inferences.
Miller v. ITT Arctic Services,
VACATED and REMANDED.
Notes
. After the notice of appeal was filed, but before any briefs were submitted, we decided
City and Borough of Juneau v. Thibodeau,
. On remand prior to our decision, the Board again awarded compensation to Smallwood.
. AS 23.30.120 provides:
“Presumptions. In a proceeding for the enforcement of a claim for compensation under this chapter it is presumed, in the absence of substantial evidence to the contrary, that
(1) the claim comes within the provisions of this chapter ...”
. See 1 A. Larson, Workmen’s Compensation Law § 10.33 at 120-21 (1978). The link is often provided by a mere showing that the injury occurred at work. Larson notes:
“It is not yet entirely clear what initial demonstration of employment-connection will give the presumption a foothold. Apparently, the idea is to rule out cases in which claimant can show neither that the injury occurred in the course of employment nor that it arose out of it, as where he contracted a disease but has no evidence to show where he got it.” (footnote omitted).
Id. at 121.
. When we spoke of the claimant’s burden of showing aggravation or acceleration in
Ketchikan Gateway Borough v. Saling,
. See, e. g., Rogers Elec. Co. v. Kouba,
. Appellant’s remaining contention, that Small-wood’s claim for acute renal failure does not constitute an “accidental injury” or “occupational disease” within the coverage of the Worker’s Compensation Act, should be readdressed to the Board on remand.
