For plasma TNF-α detection, should EDTA or heparin anticoagulant be used? Which kit should be selected for low-concentration samples?

For low-concentration plasma samples, do not dilute at the conventional 1:2 or 1:5 ratio specified in the instructions; prioritize testing with neat samples. If the background is elevated, use standard diluent plus matched anticoagulant blank plasma as a matrix control. Dilution is only required when the sample concentration exceeds the ULOQ, and after dilution, the result should fall within the mid-range of the standard curve. Data previously below the lowest point should not be forcibly extrapolated, as the results may be unreliable. It is recommended to retest with a kit having a lower LLOQ or consider a more sensitive platform.

EDTA plasma and heparin plasma may both affect TNF-α detection, but most kits are more compatible with EDTA, while heparin sometimes interferes with antibody binding, resulting in low recovery. It is recommended to first use normal plasma with EDTA/heparin added separately for low, medium, and high spike recovery tests; if the sample anticoagulant has already been fixed, validate according to the actual sample and do not change it casually. Previously, many values were below the lowest point of the standard curve, mainly due to insufficient sensitivity or excessive dilution of the sample, and the anticoagulant effect may have been a secondary factor.

Upon arrival, first use the same batch of plasma to perform unspiked, low-, medium-, and high-spike, and EDTA/heparin parallel small-sample validation. Pay attention to LLOQ and ULOQ: human TNF-α high-sensitivity kits commonly have an LLOQ of 0.5-2 pg/mL and a ULOQ of 250-1000 pg/mL. For clinical trial samples, record the anticoagulant type, centrifugation time, and cryopreservation conditions, and avoid repeated freeze-thaw cycles; before measurement, centrifuge uniformly to remove fibrin. If conventional ELISA is indeed not sensitive enough, samples may be sent out for testing on MSD or CBA platforms.

For standard ELISA standard curves, the lowest point is often 7.8 or 15.6 pg/mL, and TNF-α levels in healthy human plasma are typically below this threshold. It is recommended to choose high-sensitivity versions, such as R&D Quantikine HS, BioLegend high-sensitivity, or MSD electrochemiluminescence platforms. Inquire about the LLOQ: high-sensitivity kits may achieve an LLOQ of 0.5-1 pg/mL, and some domestic high-sensitivity kits can also reach 1-2 pg/mL. Sixty samples is not a large number; if the budget allows, purchase small packaging, or find a service provider to test multiple factors.