What code designates a transfusion for an infant weighing 3 kg?

The proper code for designating a transfusion for an infant weighing 3 kg is 36430-63. This code specifically refers to the administration of blood products, which is relevant in this context of transfusion. The addition of the -63 modifier indicates that the procedure is performed on a patient who is not the typical patient for whom the procedure is performed, aligning with the specific situation of treating an infant.

When considering the other options, 25031 pertains to diabetic foot care and is not related to transfusions or procedures involving blood products. The code 66984-RT is associated with cataract surgery with an intraocular lens implant, thus unrelated to the process of transfusion. Lastly, 51728 is a code used for procedures involving bladder catheterizations, which also does not pertain to blood transfusions.

In summary, 36430-63 is the correct choice as it directly relates to blood transfusion procedures, making it the appropriate code for an infant in this scenario.