People in North America tend to consume too much calcium and sodium and insufficient magnesium and potassium. This is often reflected in urine tests which show calcium and sodium being excreted while magnesium and potassium are being retained. (This is why we are not interested in urine pH. An alkaline urine simply shows that some alkaline minerals are being discarded by the body. Of much greater interest is the pH of saliva, which reflects your success in creating an alkaline condition within your body.)
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Even if the above were true, pH testing of urine would still be useful for detecting very acidic urine.