In high-sensitivity troponin assays, the specificity of the antibodies utilized is of utmost importance. As the clinically relevant concentration of cardiac troponin T is just nanograms per litre, even a minor cross-reactivity of the assay to skeletal troponin T isoforms could result in false positives. This was recently proved in a study of patients with skeletal myopathies (Schmid et al., 2018).

We have recently developed three new anti-cTnT MAbs (300cc, 329cc and 406cc, Cat.# 4T19cc) and showed that the prototype assays utilizing these MAbs demonstrate a good correlation with the commercially available hs-cTnT assay. Using purified recombinant skeletal TnT proteins we now show that the MAbs demonstrate negligible cross-reactivity to both fast and slow isoforms of skTnT.

First, individual MAbs were incubated with purified native cTnT and a mixture of recombinant slow and fast skTnT proteins. All three MAbs recognized only cTnT (see Figure 1). Second, we tested the cross-reactivity of the two prototype assays to purified native skTnT, recombinant fast skTnT and recombinant slow skTnT. Also in this case the cross-reactivity was well below 0.1% (see Figure 2).

Figure 1: 50 ng of cTnT or a mixture of two skeletal isoforms (1:1; slow and fast skTnT) was coated on microtiter plate wells. Primary MAb was anti-cTnT as denoted in the picture. Secondary antibody was HRP-conjugated goat anti-mouse polyclonal antibody. Substrate: TMB.

Figure 2: We tested the cross-reactivity of two prototype assays to several biomarkers including fast and slow skeletal TnT and purified native skTnT. The results show that both assays show negligible cross-reactivity to all markers tested. In hs-cTnT immunoassays the cross-reactivity should be < 0.10 % and preferably < 0.05-0.03 %.IGFBP-4 and MPO were used as negative controls.

Products:
Cat# 4T19cc: cTnT, human, antibody, in vitro
Cat# 8RFT4: Recombinant human fast skeletal troponin T (fast skTnT)
Cat# 8RST2: Recombinant human slow skeletal troponin T (slow skTnT)
All cTnT and other cardiac marker related products

TechNotes:
Cardiac troponin T (cTnT) TechNotes

References:
Schmid, J. et al. Elevated Cardiac Troponin T in Patients With Skeletal Myopathies. Journal of the American College of Cardiology 71, 1540–1549 (2018).