Had blood in urine then passed sac with white tissue 4 weeks later. Got hCG test 3 weeks after it was negative. Was this miscarriage?

May not be from urin. You had your HCG shut that could sometime caused vaginal bleeding and may be the spot you discovers might not be from urine the shut does not effect kidney see your GYN and they can assure or run a urine test with catheter to make sure it is from urine if it is they will run the appropriate testing good luck.