Figure 3. Heat inactivation of plasma or serum samples has no significant impact on detection of nucleocapsid antibodies.

A subset (n=38) of plasma samples from patients with COVID-19 including samples from PCR-positive patients from very early infection (less than 8 days) and at later times after initial infection were analyzed. Levels of antibody to the nucleocapsid protein were determined by LIPS for aliquots of paired samples from unheated plasma or serum and from heated plasma or serum. Antibody levels were plotted, and the horizontal and vertical dotted lines represent the cutoff values for seropositivity. The diagonal line is a theoretical value if the antibody levels were identical for heated and unheated samples. The antibody values strongly correlated for heat treated and not heat-treated samples as shown by the Spearman rank correlation (Rs) of 0.92 (P <0.0001) and only one sample showed a significant decrease with heating.