Table 4.

Potential use of tests to enhance the reference standard. Information in the table refers to hypothetical combinations of results in which the enhanced reference standard result would be considered different from the original reference standard result. A cell-by-cell interpretation of each scenario follows.

	Minimise FN for current infection		Minimise FN for past infection
Visit (day)	1 (0)	2 (28)	1 (0)	2 (28)
SARS-CoV-2 RT-PCR	Negative (FN)	N/A	Negative	N/A
COVID IgG	Negative	Positive	Negative (FN)	Positive
Or:	Subsequent positive SARS-Cov-2 RT-PCR result (within 28 days)		-
Or:	Hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause		Hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause
	Minimise FP for current infection		Minimise FP for past infection
Visit (day)	1 (day 0)	2 (28)	1 (day 0)	2 (28)
SARS-CoV-2 RT-PCR	Positive (FP)	N/A	Negative	N/A
1.1.35. COVID IgG	Negative	Negative	Positive (FP)	Negative
And:	No subsequent positive SARS-Cov-2 RT-PCR result (within 28 days)		-
And:	No hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause		No hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause

Minimise FN (false negative) for current infection: If the COVID-19 RT-PCR reference test gives a negative result, it can be considered a false negative if the IgG result is positive at 28 days (newly positive or titres have increased), OR if a subsequent SARS-Cov-2 RT-PCR result (within 28 days) was observed, OR if there was a hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause

Minimise FP (false positive) for current infection: If the COVID-19 RT-PCR reference test gives a positive result, it can be considered a false positive if the IgG result is negative at both baseline and 28 days, AND if no subsequent SARS-Cov-2 RT-PCR result (within 28 days) was observed, AND if there was no hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause

Minimise FN (false negative) for past infection: If the baseline reference IgG test result is negative, it can be considered a false negative if the 28-day IgG test result is positive, OR if there was a hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause

Minimise FP (false positive) for past infection: If the baseline reference IgG test result is positive, it can be considered a false positive if all other tests at baseline and at 28 days are negative, AND there has been no hospital admission or death (within 28 days) citing SARS-CoV-2 as probable cause