DEAR DR. ROACH: Last summer, a city policeman came to my door. My doctor had been unable to contact me with the results of a recent blood test and called the police. The policeman handed me a card with the results written on it. My creatinine level was 4.1, and my glomerular filtration rate (GFR) was 14. He said the numbers indicated that my kidneys were failing and that I should go to the emergen…