Identifying delayed separation in plasma homocysteine specimens

The delayed separation of plasma from the cellular components of blood can lead to falsely elevated homocysteine results. The incidence of delayed sep aration in patient specimens was examined by using the ratio of arginine to the sum of arginine plus ornithine [arg/(arg + orn)], a ratio <0.50 being consistent with delayed separation. Two groups were examined: 1) low homocy steine (<10 mu mol/L, n = 10), and 2) elevated (>18 mu mol/L, n = 12). Spec imens in the low group showed an average ratio of 0.47, with 6 of 10 <0.50. In contrast, specimens in the elevated group showed an average ratio of 0. 31, with 11 of 12 <0.50. Characteristics consistent with delayed separation occurred frequently but were significantly more frequent (p = 0.009) in th e elevated group. This suggests that many homocysteine results may be false ly elevated due to preanalytic collection problems.