Hello. I recently went to the doctor for pain in my right back thinking it may be caused by my kidney. I had a urnine  dip taken and everything came out negative. However, my urine sample only contained the first part of my urine since the cup could not hold it all. Im afraid the urine dip may not have been accurate because of this. Also, Ive noticed now my urine has been foamy no matter how much water I drink, so Im wondering if I should go see my doctor again since I feel discomfort where my kidney is on the right. Im also suffering from a sinus infection from a cold. Thank you for your help.
Infection anywhere in the body may involve kidney that can cause leakage of protein which may produce frothy urine. But remember most common cause for frothy urine is washing toilets with detergent. But better to consult nephrologist and simple 24hr urine protein estimation could solve your problem. All the best. If you have any questions feel free to contact me.