Table 2. Proposal for the interpretation of results from different diagnostic and follow-up tests in COVID-19.

Test results							Clinical significance
PCR Sputum	PCR (NPS)	PCR (Stool) *	CRISPR test **	Antigen Test	IgM	IgG
-	-	-	-	-	-	-	No infection
+	+	+	+	-	-	-	Early infection phase (acute infection)
+	+	+	+	+	-	-	Early infection phase (acute infection, symptom onset)
+	+	+	+	+	+	-	Acute infection phase
+	+	+	+	+	+	+	Acute infection (beginning of transition to late infection or convalescent phase
+	+	+	+ ***	-	-	+	Late infection phase beginning
+	-	+	+ ***	-	-	+	Late infection phase
-	-	-	+ ***	-	+	+	Active disease progression
-	-	-	+ ***	-	-	+	Late infection (past?)
-	-	-	-	-	-	+	Past infection (immunity?)
-	-	-	-	-	+	-	False positive ****

Abbreviations: COVID-19, coronavirus disease 2019; CRISPR, clustered regularly interspaced short palindromic repeats; IgG, immunoglobulin G; IgM, immunoglobulin M; NPS, nasopharyngeal swab; PCR, polymerase chain reaction.

Note: Test for IgM titers, PCR in urine or stool, as well as determination of urinary or fecal antigens, and even virologic culture, are not available in general laboratories (limited only to reference or research).

Table generated based on the Protocolo de Actuación de la Junta de Castilla y León . ⁴⁸

^* PCR positivity in stool was observed (57%) infected patients and remained positive in stool beyond nasopharyngeal swab by a median of 4 to 11 days but was unrelated to clinical severity. It may remain positive for over 6 weeks clinical relevance is uncertain (not related to severity of the disease). ⁴⁹

^** CRISPR test detects 100 copies severe acute respiratory syndrome coronavirus 2 virus (97% sensitivity/100% specificity). ⁵⁰

^***CRISPR test needs to be evaluated in these situations.

^****Need to retest