dissenting.
I am unable to join in the Court’s opinion for several reasons. First and foremost, the Commission appears to be flying by the seat of its pants in ISIF cases. In this case, the Commission concludes that Hope’s “medical records provide insufficient basis from which to draw [the] conclusion” that his 2000 impairment combined with his 2003 injury “such as to trigger ISIF liability.” The Commission implies that a physician must directly opine on this ultimate question. However, in Corgatelli v. Steel West, Inc., 157 Idaho 287, 335 P.3d 1150, 2014 WL 4198197 (Idaho Aug. 25, 2014), just released by the Court, we disapproved of the Commission’s determination of ISIF liability based solely upon its own examination of medical records without supporting medical opinion. Id. at 296, 335 P.3d at 1159, *11. In neither case did the Commission utilize the “but for” test that has been approved and applied by this Court in numerous cases.1 See Garcia v. J.R. Simplot Co., 115 Idaho 966, 970, 772 P.2d 173, 177 (1989) (“We acknowledge that the ‘but for’ standard is the appropriate test to determine whether the total permanent disability is the result of the combined effects of the pre-existing condition and the work-related injury.”) We vacated the Commission’s decision in Corgatelli for its failure to apply the “but for” test. I would do likewise in this case.
Further, the Commission misconstrued the opinion of Dr. Ward, Hope’s medical expert. Dr. Ward did not testify before the Commis*575sion but stated his opinion in a letter introduced into the record. Hope, however, did testify before a Commission referee, stating that the 2000 injury to his right shoulder cut his ability to do his job by half, while the 2003 injury made it impossible to lift anymore. This testimony was completely ignored by the Commission even though the Commission found Hope to be a credible witness and that “[h]is descriptions of his physical symptoms and capabilities were also persuasive.”
In its Corgatelli decision (Corgatelli v. Steel West, Inc. IC 2005-501771 (Idaho Ind. Com. July 26, 2012)), the Commission determined that ISIF was liable for a portion of a claimant’s total disability despite the absence of any medical opinion indicating that the claimant’s 1994 impairment combined with a 2005 injury. The claimant, Corgatelli, had been assigned a 5% whole person impairment rating in October of 1995 for the 1994 injury, resolving the claim in a lump sum settlement agreement. In August of 2010, Corgatelli was assigned a 15% whole person permanent impairment rating for the 2005 injury. There was no medical testimony that the total disability award was a result of the combination of the two impairment ratings. Indeed, the Commission made its determination based upon its own review of medical records.
The medical testimony in Corgatelli seemed to indicate that the claimant’s impairment and disability was entirely related to his second accident. According to the Commission findings:
We recognize that Dr. Simon has stated that the limitations/restrietions defined in the [functional capacity evaluation] are related to the January 3, 2005 accident. At first blush, this appears to support a conclusion that it is the 2005 accident, standing alone, and without contribution from the preexisting impairment, that renders Claimant totally and permanently disabled. If true, then there can be no “combining with” and the claim against the ISIF would fail on this element of the prima facie case. However, Dr. Simon was not examined about this statement at the time of his deposition, and it is not entirely clear that his intentions in making this statement are as described by the ISIF.
Dr. Simon was completely aware of the 1994 injury and erroneously thought that Corgatelli had received a 12% PPI rating for it, but appeared to assign all of Corgatelli’s impairment to the 2005 injury and made absolutely no comment regarding a combination of the two injuries.
Dr. Simon, according to the Commission, “rated Claimant’s permanent impairment due to his back condition attributable to his industrial injury at 15% of the whole person.” It continued: “Dr. Simon did not express an opinion on the question of whether Claimant’s impairment should be apportioned between the effects of the 2005 accident and Claimant’s preexisting condition.” Nevertheless the Commission concluded, after looking at the claimant’s medical records, that “[because Claimant’s surgery was necessitated by both the subject accident and Claimant’s preexisting condition, and because Claimant had a poor surgical outcome, such that he is currently totally and permanently disabled, it is clear that the combining with element of the prima facie case has been met.” Thus, contrary to the Commission’s apparent holding in the present case, medical testimony was not necessary in Corgatelli to establish the “combines with” element.
This certainly has the appearance of arbitrary action on the part of the Commission. It is not clear what caused the Commission to determine ISIF liability based on its perusal of medical records in Corgatelli, while declining to do so in this case. Indeed, this is a stronger case because there is expert medical testimony on the “combined with” issue. The Commission just misread it.
In his letter, Dr. Ward opined in pertinent part:
I have examined Mr. Hope and reviewed his medical records with the intent of rendering a permanent impairment based on the AMA Guides to the Evaluation of Permanent Impairment 5th edition.
As you are aware Mr. Hope had a prior injury and prior surgery on his shoulder, so there is some pre-existing impairment *576that must be addressed in regard to the shoulder.
His current shoulder impairment is 8% whole person with 3% Whole person preexisting, for a total of 5% whole person for the current injury----
It must be noted with .this last injury and surgery, Mr. Hope has significant disability. To put it bluntly his shoulder is pretty well trashed!
(emphasis added). The Commission construed this to mean that Hope “would be totally and permanently occupationally disabled as a result of his December 2003 right shoulder injury, alone.”2
The Commission’s interpretation of Dr. Ward’s opinion is rather strained. Dr. Ward did not testify so there is no need to give deference to the Commission’s incorrect reading of his letter. He states that the “pre-existing impairment ... must be addressed in regard to the shoulder.” He documents the 3% whole person pre-existing impairment. There would be no point in saying the pre-existing impairment must be addressed if it played no role in trashing his shoulder.
While Dr. Ward did not use the magic words “combined with” when stating his opinion as to Hope’s right shoulder impairment, it is clear that was the gist of what he was saying. According to Dr. Ward, Hope’s “current shoulder impairment is 8% whole person with 3% Whole person pre-existing, for a total of 5% whole person for the current injury.” That is, he calculated Hope’s impairment following the 2003 injury at 8%, determined that 3% of that was a result of the 2000 injury, calculating an impairment of 5% for the 2003 injury. Looking át it another way, the 3% impairment, plus the 5% impairment, equaled the -8% impairment or, as my grade school math teacher would have put it, 3 combined with 5 equals 8. Dr. Ward continued: “It must be noted with this last injury and surgery Mr. Hope has significant disability. To put it bluntly, his shoulder is pretty well trashed!” It is rather clear Dr. Ward meant that the 3% existing impairment from 2000 combined with 5% from 2003 equaled a trashed shoulder. Contrary to Dr. Simon in the Corgatelli ease, Dr. Ward did apportion Hope’s impairment between the two injuries.
This reading of Dr. Ward’s letter is consistent with Hope’s own testimony, which the Commission completely ignored. Although in Corgatelli it searched the record for evidence to support its finding of ISIF liability, it did not consider pertinent testimony submitted here by Hope. Certainly, a credible worker’s compensation claimant’s testimony should be considered in determining whether a preexisting impairment combines with a new injury to result in ISIF liability. In Garcia, the Court noted that “medical and lay testimony” supported a finding that a claimant “had pre-existing permanent physical impairments.” 115 Idaho at 968-69, 772 P.2d at 175-76. Indeed, a claimant’s testimony can play a critical part in the determination of a worker’s compensation claim. See Stevens-McAtee v. Potlatch Corp., 145 Idaho 325, 331-32, 179 P.3d 288, 294-95 (2008). There is no reason why a credible claimant’s testimony should not play an important part in a case involving potential ISIF liability. After all, the claimant is the person best positioned to testify as to how he or she has been affected by each of multiple injuries.
Hope testified that he had suffered substantial impairment of his right shoulder as a result of his 2000 injury and that with the additional 2005 injury he could no longer perform his job.3 During the April 5, 2012 hearing, Hope testified as follows regarding *577the status of his shoulder prior to the 2003 injury: .. .
Oh, yeah. I had shoulder pain, and I didn’t have the strength that I did before____ It’s, it’s gradually deteriorated through time. I wasn’t back the hundred percent when they, wanted me to go back to work in the first place from my first surgery.
He testified that he could not carry rebar on his right shoulder after, the 2000 injury. He testified he could use a nail gun with that shoulder prior to the 2003 injury but not afterwards. He stated that after the 2003 injury “it just got to where I could not even lift my arm up. And I told Marty, ‘I’m done.’ ” In a deposition taken May 11, 2006, he testified that after the 2000 injury he “[cjouldn’t lift near the weight that I could before. I didn’t have my strength.” When asked what his limitation was, he replied “I’d be — I’d feel safe in saying half.” I was cut in half, good half, of my ability to do my job. He testified that after the 2003 injury:
I couldn’t lift no more. And I told him, I says, “I’m done, Marty.” I says, “My shoulder won’t even lift anymore.” I says, “I’ve got to go back to the doctor,” And that was my last day.
Although Hope did not use the words “combined with,” the import of his testimony is clear. He suffered substantial limitations on his ability to use his right shoulder in performing his work as a result of the 2000 injury and the additional injury in December of 2003 added to those limitations to the extent of making it impossible to continue doing his job.
It is odd that the Commission did not take this testimony into account because it was not contradicted in any way and the Commission specifically found Hope’s “descriptions of his physical symptoms and capabilities ... persuasive.” We have oft held that a Commission referee “must accept as true the positive, uncontradicted testimony of a credible witness----” Mazzone v. Texas Roadhouse, Inc., 154 Idaho 750, 758, 302 P.3d 718, 726 (2013).
As we have done with Corgatelli, I would reverse the decision of the Commission for failure to apply the “but for’-’ test, for misunderstanding the import of Dr. Ward’s opinion letter and for ignoring pertinent, credible testimony presented by Hope.
Justice W. JONES concurs.. In its decision in this case, the Commission did cite Garcia and another "but for” case (Bybee v. State, Indus. Special Indent. Fund, 129 Idaho 76, 921 P.2d 1200 (1996)), but it did not mention or apply the "but for” test.
. Had this been the purport of Dr. Ward’s letter, he could simply have stated that the 2003 injury trashed Hope’s right shoulder. There would have been no need to pointedly mention the preexisting impairment or to apportion impairment between the two injuries. The Commission appears to be putting words into Dr. Ward's mouth that he did not utter in his letter. On the other hand, in Corgatelli, where it appeared that Dr. Simon did assign all of the claimant's impairment to the last injury, the Commission supplied wording to the contrary in order to establish ISIF liability. In neither case should the Commission have supplied any extraneous wording to the doctor’s opinion.
. Indeed, the Commission specifically found that "Claimant has proven his right shoulder constituted a substantial hindrance [to employment] prior to his December 2003 industrial injury.”