Urine and blood acidity is often confused by alkaline diet supporters.
Many online lay-men and sources believe that body acidity (or blood acidity) is the cause of many health issues and to test it you can use urine or saliva.
Irrespective whether that theory is correct or not, this myth is busted as a urine pH test is not an indicator of the alkaline balance in your body.
Blood pH is tightly controlled by a number of mechanisms in the body and must stay in equilibrium.
Only by using blood samples, it is possible to determine the blood pH.
Please note, however, that testing blood pH is useless, unless you have some related underlying medical condition. Dietary changes will not cause your blood pH to fluctuate.
One of the ways that this equilibrium is controlled is by removing through the urine the excess of ions from the system by the kidneys. These ions, depending on their charge, can make urine more or less acidic.
Therefore, when you measure urine pH you are measuring what was excreted from the body in order to maintain that equilibrium rather than the acid-alkaline balance of the blood. (1, 2, 3, 4)