Bioactive TGF-β levels can be preserved in plasma samples collected into heparin but not EDTA

Quantifying TGF-β is important for many research areas since its effects often are dose-dependently bidirectional. The post-transcriptional control of TGF-β bioavailability points out the need to determine TGF-β at the protein level. Studies measuring TGF-β in peripheral blood have to avoid contamination with platelet-derived TGF-β. Techniques to obtain platelet-poor plasma have been suggested, however, the impact of different anti-coagulants on artificial TGF-β contamination has not been studied in detail. Here, we compare TGF-β levels in blood samples collected into heparin and EDTA tubes, stored for 0.5–18 h at various temperatures. We show that contamination with latent TGF-β can only be prevented by collecting the sample on ice. Importantly, levels of bioactive TGF-β in blood collected into heparin but not EDTA tubes remained stable up to 18 h, even when kept at RT. Further in vitro experiments indicate that heparin prevents the activation of latent TGF-β into its bioactive form probably by virtue of accelerating the complex-formation between AT-III and thrombin. Where precise measurement of latent TGF-β in blood samples is required, samples need to be collected on ice; bioactive TGF-β can be detected reliably in samples collected into heparin tubes even when stored at RT.