I am using Abnova's corticosterone ELISA kit (catalog no. KA0468) to quantify plasma CORT levels in samples collected from stressed mice. Some of my samples are so low in volume that I have to add SBS diluent in order to bring them to the necessary volume (25 ul) before loading them into the plate, and I am accounting for this dilution factor in my final calculations. Additionally, the blood samples are been collected into tubes precoated with 10 ul of heparin, but the amount of blood collected is such that the final volume in the tube is, on average, 33% heparin. My levels of CORT from the unstressed control animals are much lower than what is seen in the literature, and I'm trying to determine why this might be. Could the heparin potentially be interfering with the detected levels of CORT, and should I account for the amount of heparin in the initial sample tube as a dilution factor?