What can cause false changes in urine specific gravity readings on dipstrip testing?

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The key idea is that the dipstrip’s specific gravity reading comes from a color change of a chemical indicator that responds to the urine’s ionic strength and composition. Because the indicator’s response depends on its protonation state, changes in urine pH can shift the indicator’s pKa in alkaline conditions, altering the color in a way that biases the SG value. This makes the reading less reliable if the urine is not neutral.

High protein content and acidic urine modify the sample’s ionic environment, which can push the color change toward indicating a higher density than is actually present (a false high). Conversely, in alkaline urine, the same indicator can respond in a way that makes the SG appear lower than it truly is (a false low). So false changes in SG on dipstrip testing mainly come from how urine pH and solute constituents interact with the strip’s indicator.

Other factors like temperature drift can affect some measurements, but bilirubin or high glucose mainly impact their specific tests rather than the SG reading itself.