The 13-digit national identification number (matricule) must be indicated on each original medical certificate of incapacity for work sent to the CNS. If the doctor did not mention this number on the certificate, the insured person may add it themselves.
This number can be found on either the declaration of entry (déclaration d'entrée) issued by the Joint Centre of Social Security (Centre commun de la sécurité sociale) or the Luxembourg social security card.
As of 1st of August 2017, the department in charge of cash benefits (département des Prestations en espèces) will no longer be able to process documents which do not contain this number.