Hi and thanks for your question,
Did your doctor advise against breast feeding due to the medication you are taking for your hydronephrosis? If so, what antibiotic are you taking and how long will you be taking it.
It is great that you are continuing to pump your breast milk with the intention of picking up breast feeding your baby as soon as you are able.
Unfortunately the United states does not have a breast milk monitoring program and there is no central lab for women to send their milk for testing. You should check with your doctor on the time frame you will be unable to nurse and the possibility of finding a lab to test your milk.
If the duration is significant you can consider donated breast milk to ensure your baby is getting all the benefits of breast milk.
La Leche League has great information www.llli.org