Figure 8. Heparin-induced release of lipase in vivo can lead to in vitro generation of non-esterified fatty acids during sample incubation or storage. An increase in serum non-esterified fatty acid (NEFA) concentrations to >3 mmol/l is sufficient to displace T4 from thyroxine binding globulin, but such values are uncommon in vivo. This artefact is accentuated by high triglyceride or by low albumin concentrations.