LCT and hand, foot and mouth disease: Otherwise, according to this study, combining the serum 25(OH)D concentrations with the PCIS and other indicators, such as LAC, LDH, CK-MB and DD, may help to evaluate the condition of critical and severe HFMD, and monitoring the serum 25(OH)D concentrations in children with critical and severe HFMD may assist in determining the progression and prognosis of the disease.