Most fevers in babies are caused by infections, including viral, bacterial, chlamydial, fungal and other infections. A normal blood test in a baby with fever mostly indicates a viral infection, but other microbial infections such as mycoplasma and chlamydia cannot be ruled out and need to be combined with other related tests. Viral infections can cause many diseases. If a baby has a fever accompanied by nasal congestion, sneezing, runny nose, cough, chills and other symptoms, it is most likely that the viral infection is caused by upper respiratory tract infection, bronchitis, and bronchopneumonia and other respiratory tract diseases. There are also autoimmune deficiency diseases and endocrine metabolic diseases, which can also cause fever, and the blood tests are mostly normal, but the baby will show symptoms of related diseases and abnormal related tests. There are also some fever of unknown cause, blood routine is also usually normal, you need to go to the hospital to do relevant tests to clarify the diagnosis.