She is of 33 years on ATT for three and half months developed white coating like curd on tongue and a rash on hand in overnight, she having mild fever for one day, no medicine for fever given. She is a clerk. On rifampin Isonex PZA and ethebutol ( extra pulmonary tb + pleural tb)Test HIV negative done in February.

What test to done urgently? And what's it, please suggest?