Individuals who hold refugee status and who are not lawful permanent residents must have a Refugee Travel Document to have the right to re-enter the USA after travel abroad (unless they possess an Advance Parole Document).
Thus, before travelling outside the USA you must file Form I-131, Application for Travel Document, and wait till USCIS approves it. Besides, after filing your Form I-131, you will have to attend in person the biometrics services appointment.
The processing time of Form I-131 is approximately 3 months, so if you are in a hurry and have an emergency situation, you may request an expedited processing to receive your Refugee Travel Document faster.
In case you do not receive a Refugee Travel Document before you leave the United States, you may be unable to return to the USA or you may be placed in removal proceedings before an immigration judge. If you still need to leave the USA before you obtain your Refugee Travel Document, you should consult with an immigration attorney.