Rubella can usually be initially diagnosed by the typical symptoms and characteristics of the rash, together with a viral test of pharyngeal secretions, or a serum antibody assay. The peripheral blood picture can also be used as a reference. Lymphocytosis is usually increased and heterogeneous lymphocytes may also be present. If the rash appears one day after the onset of fever, the rash first appears on the head and face and then gradually spreads to the trunk and extremities.