Sheikh Uthaimeen رحمه الله mentioned that the Râfidah are from the Shia sect. The Shia are basically general and the Rafidah are specific. Every Shia is not a Râfidah and but every Râfidah is from the Shia sect. Râfidah are considered disbelievers.
"The Râfidah are NOT considered brothers of the Muslims because they are disbelievers."
Therefore the Râfidah are NOT considered from the 73 sects.
They are disbelievers. They are called Râfidah from the word '(rafada)' which means 'to rejector or refuse.' The Râfidi rejected Zayd ibn ‘Ali ibn Hussein. The Râfidah insult Abu Bakr and Umar رضي الله عنهم and make them disbelievers saying that they disbelieved after Iman. The Râfidah came to Zayd ibn Ali to inquire after Abu Bakr and Umar رضي الله عنهم and Zayd praised them replied that: 'they were both ministers of my grandfather.' Because of this statement they then rejected Zayd ibn Ali. They claim love for Ahl-al-Bayt -- praising them and going overboard in their love for them.