Coronavirus disease 2019 (COVID-19) pandemic continues devastating effects on 
healthcare systems. Such a crisis calls for an urgent need to develop a risk 
stratification tool. The present chapter aimed to identify laboratory and 
clinical correlates of adverse outcomes in patients with COVID-19. To this end, 
we conducted a systematic evaluation of studies that investigated laboratory 
abnormalities in patients with COVID-19 and compared i. patients with a severe 
form of disease and patients with a non-severe form of the disease, ii. patients 
who were in critical condition and patients who were not in critical condition, 
and iii. patients who survived and patients who died. We included 54 studies in 
the data synthesis. Compared to patients with a non-severe form of COVID-19, 
patients who had a severe form of disease revealed higher values for white blood 
cells (WBC), polymorphonuclear leukocytes (PMN), total bilirubin, alanine 
aminotransferase (ALT), creatinine, troponin, procalcitonin, lactate 
dehydrogenase (LDH), and D-dimer. By contrast, platelet count, lymphocyte count, 
and albumin levels were decreased in patients with a severe form of COVID-19. 
Also, patients with a severe phenotype of disease were more likely to have 
diabetes, chronic heart disease, chronic obstructive pulmonary disease (COPD), 
cerebrovascular disease, hypertension, chronic kidney disease (CKD), and 
malignancy. Compared to patients who survived, patients who died had higher WBC, 
PMN, total bilirubin, ALT, procalcitonin, IL-6, creatinine, PT, lymphocyte 
count, platelet count, and albumin. Also, non-survivors revealed a higher 
prevalence of diabetes, chronic heart disease, COPD, cerebrovascular disease, 
and CKD. Meta-analyses identified several laboratory parameters that might help 
the prediction of severe, critical, and lethal phenotypes of COVID-19. These 
parameters correlate with the immune system function, inflammation, coagulation, 
and liver and kidney function.