HIGHER operating costs have led to a 37 per cent increase in rates at out-patient clinics, according to the Acting Secretary for Health and Welfare, Dr Lee Shiu-hung. The rise is 20 per cent higher than the 17 per cent average annual increase over the past five years. Dr Lee said out-patient clinics under the Hospital Authority had suffered from a higher cost increase than other medical facilities. ''Twenty-two per cent of the 37 per cent was due to the increase in costs.'' The money was used to upgrade facilities at the 57 clinics offering out-patient services, he added. Legislator Dr Conrad Lam Kui-shing questioned the large discrepancy between this year's figures and the average over the past five years. ''Why have the figures fluctuated so much? While there was an average 15 per cent increase in rates for specialist out-patient clinics during the past five years, this year it was only 7.5 per cent,'' Dr Lam said. Dr Lee, however, insisted the figure was a reflection of the change in one year. He said the full-cost approach used in calculating the authority's medical costs included staff costs, drugs and consumables. ''The use of resources at hospital level is then monitored and evaluated by the head office,'' said Dr Lee.