Table 2 Predictive accuracy of individual isotypes for classifying controls and cases across time.

IsotypeDays since symptom onsetAUC (95% CI)Sensitivity (95% CI)
IgG≤7 days0.68 (0.66–0.70)0.07 (0.03–0.12)
8-14 days0.91 (0.89–0.92)0.51 (0.43–0.58)
15-28 days0.99 (0.99–1.00)0.95 (0.92–0.98)
>28 days0.99 (0.99–1.00)0.95 (0.91–0.98)
IgA≤7 days0.63 (0.61–0.65)0.07 (0.03–0.11)
8-14 days0.87 (0.85–0.89)0.44 (0.38–0.51)
15-28 days0.98 (0.97–0.98)0.89 (0.84–0.94)
>28 days0.98 (0.97–0.98)0.60 (0.51–0.68)
IgM≤7 days0.60 (0.58–0.62)0.08 (0.03–0.13)
8-14 days0.87 (0.85–0.89)0.55 (0.48–0.62)
15-28 days0.98 (0.97–0.99)0.86 (0.81–0.92)
>28 days0.93 (0.91–0.94)0.51 (0.43–0.59)

The isotype cut-offs chosen for calculating sensitivity were the maximum value found among pre-pandemic controls (IgG: 0.57 μg/mL, IgM: 2.63 μg/mL, IgA: 2.02 μg/mL). Bootstrap 95% confidence intervals are shown in parentheses.