Table 1.

Overview of potential risk biomarkers for COVID-19

Group	Marker	Reference	Level of Evidence	Comments
Hemostasis	D-dimer	[20,26,38–41]	High	Heart involvement
Acute phase reactant	Procalcitonin	[39,42–44]	Moderate
	Ferritin	[27,35,76]	Moderate	Marker of HLH, MAS
	CRP	[26,27,44]	High	Low specificity, in combination with diagnosis of COVID-19 (currently) strongly predictive
Cytokine	IL-6	[21,25,44]	Moderate	Associated with ‘cytokine storm’ in COVID-19
COVID-19 related markers	Anti-SARS-CoV-2 antibodies (isotypes)	[45,46]	Limited	Ratio between isotypes might indicate severity; IgA might play important role in COVID-19 severity
	Viral load in RT-PCR	[10]	Moderate	Long turn-around time
Inflammatory protein	Amphoterin, HMGB1	[34,47]	Limited	Released during NETosis, also discussed as therapeutic target
	Calprotectin, S100A8/S100A9, MRP8/14	[33,37]	Limited	More global/specific indicator of PMN and monocyte activation
Autoantibodies	Anti-phospholipid antibodies	[56,59,60]	Limited	Controversial findings; further studies required
Complement system	Complement activation	[48]	Limited	SC5b-9 and C5a
Serum protein	Serum amyloid A (SAA)	[28,29,49]	Evolving	Might be useful in cases which have low CRP levels; potentially combined with IL-6
	Fibrinogen (Fib)	[50]	Moderate	Potentially combined with Albumin in ratio
	Albumin (Alb)	[41,50]	High	Potentially combined with Fibrinogen in ratio
Cardiac biomarkers	Cardiac troponin I (cTn1)	[43,51,52]	Moderate	Might predict death related to myocardial injury
Liver enzyme	Lactate dehydrogenase (LDH)	[41,53]	High	Routinely used
	Alanine aminotransferase (ALT)	[41,53]	High	Routinely used ALT might have the highest value among liver markers
	Aspartate aminotransferase (AST)	[41,53]	High	Routinely used

Abbreviations: CRP, C-reactive protein; HMGB1, high mobility group protein B1; HLH, hemophagocytic lymphohistiocytosis; IL, interleukin; MAS, macrophage activation syndrome; RT-PCR, real time primer chain reaction.