A study, including some surprising data about amputations, has determined that workers’ compensations claims for medical costs that become costlier lost time claims with indemnity payments most often involve older employees.

The research by the National Council on Compensation Insurance also found that the percentage of medical claims converting into lost time claims varies greatly among the states and that more than 20 percent of amputations never become lost time claims.

John Robertson one of the authors of the report, said the data on amputations was somewhat of a surprise. According to the NCCI data, 21 percent of all amputation claims stayed medical only.

One factor in that number, he said, was that “a tip of a finger counts as an amputation.” The amputation classification usually refers to a body part loss that occurs by surgery after injury, while the listing for “severance” refers to a loss that occurs in the course of an accident. Mr. Robertson said carrier classification might be an issue in the date.

The effect that age had on the numbers, said Mr. Robertson, was not unexpected, “We’ve seen in other studies that claims for older workers tend to cost more than younger workers.” According to the study, about 2 percent of medical claims by workers under age 25 become lost time compared with over 8 percent in the 55-to-60-year-old age range.

The top five types of injury that became lost time and the probability of their transitioning were: rupture, 69.5 percent; amputation, 36.6 percent; carpal tunnel, 33.3 percent; mental disorder, 24.5 percent, and severance, 22.7 percent.

Among the states, the percentages of medical injury conversions to long term showed some states with levels almost double the states in the lowest bracket. Highest was New York, where 8 percent of medical injuries became long term, compared with Arkansas at 2.3 percent.

Next to New York in the top five were: Hawaii, 7.6 percent; Missouri, 7.2 percent; California, 7 percent, and South Carolina, 6.8 percent.

For the study, researchers examined 5 million claims that had no lost time indemnity benefit component after three months to see which ones ultimately included lost time.

NCCI said medical-only claims account for most comp injury at 77.9 percent, but they make up only 6 percent of loss dollars. The study said many companies have medical-only units for fast tracking small medical claims, and that this has worked well. It also noted that after two and a half years, only 4.6 percent of the claims had turned into lost time claims.

According to the study, the average cost at 30 months for medical-only claims that transition to lost time is 40 times greater than the cost of medical-only claims that do not transition.

The researchers put the average cost of medical-only claims at $500, while those that became lost time claims averaged $21,100.