2.2 Laboratory testing
Specimens of nasopharyngeal swabs from children younger than 2 years old
and throat swabs from children 2 years or older were obtained for
detection of SARS-CoV-2 nucleic acid using RT-PCR assay. The testing was
performed in the clinical laboratory of the Wuhan Children’s Hospital,
and the detailed protocol had been described
previously.8
Some routine laboratory results were collected from the clinical testing
reports, including the complete blood count (CBC), and serum levels of
biomarkers such as inflammatory indicators of C-reactive protein (CRP)
and procalcitonin (PCT), the coagulation index of D-dimer, the
myocardial injury marker of creatine kinase (CK)-MB, the liver function
of alanine aminotransferase (ALT), aspartate aminotransferase (AST) and
alkaline phosphatase (ALP), and the renal function of serum creatinine
and blood urea nitrogen (BUN). Co-infections were indicated by available
detection results of other pathogens, including serological measurements
of mycoplasma pneumoniae (MP) and chlamydia pneumoniae (ChP),
immunoglobulin M (IgM) against Epstein-Barr virus (EBV), cytomegalovirus
(CMV) and adenovirus (AdV), and nucleic acid testing of influenza A and
B viruses in specimens from pharyngeal swabs. Besides, immunological
parameters were collected in detail, including total immunoglobulins
(IgG, IgA, IgM and IgE), complements (C3 and C4), peripheral blood CD4+
and CD8+ T, B and NK lymphocyte subsets count, and concentration of
serum cytokines including interleukin (IL)-2, 4, 6 and 10, tumor
necrosis factor (TNF)-α, and interferon (IFN)-γ.