Why can't I get my blood drawn from the PICC line, midline or central line?

Obtaining blood from a central line catheter, including PICC, subclavian, or tunneled catheters, necessitates a written order from a physician. Routine blood draws using peripheral-midline catheters are discouraged due to the potential for occlusion risks, such as thrombosis, mechanical blockage, or drug precipitation. Essentially, this could lead to significant blockage, necessitating the removal and reinsertion of the catheter.