NAC616C.490. Apportionment of impairments.

     1. If any permanent impairment from which an employee is suffering following an accidental injury or the onset of an occupational disease is due in part to the injury or disease, and in part to a preexisting or intervening injury, disease or condition, the rating physician or chiropractor, except as otherwise provided in subsection 9, shall determine the portion of the impairment which is reasonably attributable to the injury or occupational disease and the portion which is reasonably attributable to the preexisting or intervening injury, disease or condition. The injured employee may receive compensation for that portion of his or her impairment which is reasonably attributable to the present industrial injury or occupational disease and may not receive compensation for that portion which is reasonably attributable to the preexisting or intervening injury, disease or condition. The injured employee is not entitled to receive compensation for his or her impairment if the percentage of impairment established for his or her preexisting or intervening injury, disease or condition is equal to or greater than the percentage of impairment established for the present industrial injury or occupational disease.

     2. Except as otherwise provided in subsection 9, the rating of a permanent partial disability must be apportioned if there is a preexisting permanent impairment or intervening injury, disease or condition, whether it resulted from an industrial or nonindustrial injury, disease or condition.

     3. A precise apportionment must be completed if a prior evaluation of the percentage of impairment is available and recorded for the preexisting impairment. The condition, organ or anatomical structure of the preexisting impairment must be identical with that subject to current evaluation. Sources of information upon which an apportionment may be based include, but are not limited to:

     (a) Prior ratings of the insurer;

     (b) Other ratings;

     (c) Findings of the loss of range of motion;

     (d) Information concerning previous surgeries; or

     (e) For claims accepted pursuant to NRS 616C.180, other medical or psychological records regarding the prior mental or behavioral condition.

     4. If a rating evaluation was completed in this State for a previous industrial injury or occupational disease involving a condition, organ or anatomical structure that is identical to the condition, organ or anatomical structure being evaluated for the present industrial injury or occupational disease, an apportionment must be determined by subtracting the percentage of impairment established for the previous industrial injury or occupational disease from the percentage of impairment established for the present industrial injury or occupational disease, regardless of the edition of the American Medical Association’s Guides to the Evaluation of Permanent Impairment used to determine the percentage of impairment for the previous industrial injury or occupational disease.

     5. Except as otherwise provided in subsection 6, if a rating evaluation was completed in another state for a previous injury or disease involving a condition, organ or anatomical structure that is identical to the condition, organ or anatomical structure being evaluated for the present industrial injury or occupational disease, or if no previous rating evaluation was performed, the percentage of impairment for the previous injury or disease and the present industrial injury or occupational disease must be determined by using the Guide, as adopted by reference pursuant to NAC 616C.002. The apportionment must be determined by subtracting the percentage of impairment established for the previous injury or disease from the percentage of impairment established for the present industrial injury or occupational disease.

     6. If precise information is not available, and the rating physician or chiropractor is unable to determine an apportionment using the Guide as set forth in subsection 5, an apportionment may be allowed if at least 50 percent of the total present impairment is due to a preexisting or intervening injury, disease or condition. The rating physician or chiropractor may base the apportionment upon X rays, historical records and diagnoses made by physicians or chiropractors or records of treatment which confirm the prior impairment.

     7. If there are preexisting conditions, including, without limitation, degenerative arthritis, rheumatoid variants, obesity, congenital malformations or, for claims accepted under NRS 616C.180, mental or behavioral disorders, the apportionment must be supported by documentation concerning the scope and the nature of the impairment which existed before the industrial injury or the onset of disease.

     8. A rating physician or chiropractor shall always explain the underlying basis of the apportionment as specifically as possible by citing pertinent data in the health care records or other records.

     9. If no documentation exists pursuant to subsection 7 or 8, the impairment may not be apportioned.

     [Comm’r of Insurance & Industrial Comm’n, No. 41 § 9, eff. 5-13-82]—(NAC A by Dep’t of Industrial Relations, 10-26-83; 6-23-86; A by Div. of Industrial Insurance Regulation, 2-22-88; A by Div. of Industrial Relations by R009-97, 10-27-97; R105-00, 1-18-2001, eff. 3-1-2001; R108-09, 6-30-2010)