Critical is more severe than serious in describing a patient's medical condition. Both conditions may be life threatening.
According to UCLA Health, a serious medical condition describes a very ill patient with questionable indicators whose vital signs are abnormal or unstable. A condition escalates to critical if a patient's symptoms and indicators are unfavorable and may include a loss of consciousness.
The federal Health Insurance Portability and Accountability Act (HIPAA) includes patient privacy laws limiting the level of information on a patient's condition that a hospital may provide to the media. The information is restricted to general one-word definitions on an escalating scale of undetermined, good, fair, serious and critical.