Ah! so you are emigrating.
This is not my field of expertise, the New Zealand immigration rules, but here are my thoughts.
Whether blood tests are required in say someone over the age of 30years old would depend entirely on the past medical history and if that was clear, then no blood tests would be required.
Now in you particular case, they clearly have picked up this protein loss in your past history and do not want to be saddled with an immigrant who may need expensive kidney management. The tests that you mention are tests of renal function, to evaluate the condition of your kidneys.
Now from what you have said it is clear to me that your kidneys are functioning normally, you say that you are well and I cannot see any impediment on health grounds to your application.