THE RELIABILITY OF THE SERUM DIOXIN MEASUREMENT IN VETERANS OF OPERATION RANCH HAND

A study was conducted on the reliability of the serum dioxin measureme nt of enlisted Ranch Hands veterans participating in the Air Force Hea lth Study using paired serum dioxin measurements. The 46 veterans were not randomly selected, bur their demographic characteristics, health, and dioxin levels were similar to those of 404 other enlisted Ranch H and veterans who had a single dioxin measurement made in 1987. The ave rage time between the measurements was 0.61 years, the first measureme nt made from blood drawn on 10 April 1987 and the second from blood co llected at a subsequent physical examination. In original units, the c oefficient of reliability was 0.87 (95% confidence interval: 0.76, 0.9 4) when the first measurement was at or below 50 parts per trillion. T he measurement had no reliability in original units when the first mea surement was greater than 50 parts per trillion. After a logarithmic t ransformation, the coefficient of reliability was 0.96 (95% confidence interval: 0.93 to 0.98). These results suggest that the serum dioxin measurement should not be used in original units for any purpose when the value exceeds 50 parts per trillion. The measurement is, however h ighly reliable after a logarithmic transformation over the entire rang e of concentrations. Other studies using the same analytical method to measure dioxin in serum could similarly benefit if the measurement us ed is on the natural logarithm scale.