Kidney involvement and anemia in COVID-19 infection

Table 1 Typical timeline of inflammation in COVID-19¹

Phase	Days post-infection	Features	Key inflammatory markers
Viral replication phase	1-5	Mild symptoms (fever, cough, fatigue); inflammation is usually low to moderate	CRP, IL-6, ferritin may be slightly elevated
Early inflammatory phase	5-10	Worsening symptoms (dyspnea, hypoxia); immune system response intensifies	Rising CRP, IL-6, ferritin, D-dimer, LDH
Hyperinflammatory phase (if occurs)	7-14+	Cytokine storm in severe cases; respiratory failure, organ dysfunction	Very high IL-6, CRP, ferritin, D-dimer; lymphopenia
Resolution/recovery	After day 14 (mild/moderate)	Symptoms improve; inflammation resolves gradually	Inflammatory markers decrease over weeks

¹In mild COVID-19, the inflammation remains limited and subsides quickly. In severe or critical illnesses, it is the hyperinflammatory response that often leads to complications such as acute respiratory distress syndrome, coagulation disorders, or multiple organ failure. In patients with chronic diseases (e.g., chronic kidney disease), the inflammatory response may be attenuated or prolonged, which complicates the interpretation of markers such as ferritin or C-reactive protein.

CRP: C-reactive protein; IL-6: Interleukin-6; LDH: Lactate dehydrogenase.