The urine pH level does not give reliable information about the body’s acid-case status because urine pH depends greatly on food intake. In addition, it fluctuates according to the time of day (pH 5 – 8). Morning urine is usually more acidic than the urine produced throughout the day. Another factor is that less than 1% of the acid in the urine is excreted in the form of substances known as free acids.
Yet, it is only these that can be measured with pH test strips. The remaining 99% of the acids excreted in the urine therefore cannot be determined using pH strips. For this reason, it is possible to assess acid-base status from the urine only by measuring total acid excretion in a 24-hour urine collection.