All perfect praise be to Allah the Lord of the Worlds. May His peace and blessings be upon our Prophet Mohammad and upon all his family and companions.
Taking specimen and sending them to the lab for testing is the responsibility of certified and specialized medical laboratories because this a moral and religious responsibility that can lead to serious consequences.
Consequently, this task must be performed by those specialized in this field, not a nurse or someone else. This is in order to avoid violating the system that was essentially set up to preserve interests and ward off harm. The evidence on this is that it was narrated from Ibn 'Abbas that the Messenger of Allah (PBUH) said: “There should be neither harming nor reciprocating harm.” {Related by Ahmad}.
It is the duty of the nurse to give sincere advice to the patient by directing him to the lab that does the job properly and professionally. As for taking money from the patient in the form of commission, it is a betrayal of trust, even if it doesn`t involve exploiting him. This is also considered eating up people`s property unjustly since the nurse isn`t an employee of the patient`s nor a proxy of his in return for a specific pay. This is attested to in the following verse: " And eat not up your property among yourselves in vanity, nor seek by it to gain the hearing of the judges that ye may knowingly devour a portion of the property of others wrongfully." {Al-Baqarah, 188}. And Allah The Almighty Knows Best.