DEAR DR. DONOHUE: I am 83 and feel good. I take medicine for hypertension. I discussed with my doctor the results of my lab tests, and he told me I had protein in the urine. I have no idea what this means. He said he would discuss it after a repeat test. I felt good when I went into the office but left very worried. What does this mean? – E.S.

ANSWER: The kidneys are like a flour sifter that allows fine grains of flour to pass through but keeps debris out of the sifted flour. The kidneys filter small waste products into the urine but keep large, good particles like proteins in the blood. When protein appears in the urine, it’s a sign that the kidney’s filters have developed holes.

The meaning of all this depends on the amount of protein in the urine. Small amounts might be insignificant and a temporary thing. Exercise or just a slight elevation of body temperature can cause a little protein to leak into the urine. A repeat exam, therefore, is a rational approach to the problem.

Persistent protein in the urine is found in diabetes, high blood pressure, kidney ailments and congestive heart failure. Cancers like multiple myeloma can also cause protein to appear in the urine.

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