I had a urine test and came back normal complaining a burning sensation and discomfort no infection dr ordered a culture test don't know what for?

More sensitive test.: A urine culture is a much more sensitive test for bacterial infection in the urine. Tests in the clinic like a urine dipstick analysis look for indirect signs of infection (i.e. Nitrites and leukocyte esterase), but may miss a uti. In addition, a culture test will reveal which antibiotic is best to treat the infection if one is detected.