Why are my urine and saliva pH readings different?

“I measured both my first-morning urine pH and saliva pH and the readings were very different.  The saliva was in the normal green range and the urine was completely yellow. How can it be that I get different pH readings from my urine and saliva?”
Urine and saliva are very different bodily fluids. The urine carries excretion impurities, acids, and other unwanted substances filtered from the blood by the kidney.  
The pH of the urine varies throughout the day, but  is generally more acid than that of saliva. The saliva is a filtrate of the blood secreted in the mouth designed to enhance digestion.  Saliva pH is generally higher than urine, as excess acids are excreted in the urine. 
The first-morning urine pH test after at least 6 hours of sleep without urinating is the best way to estimate metabolic acid load. The ideal first-morning urine pH is 6.5 to 7.5.  
The pH of saliva can be altered by bacteria, food residue in the mouth and the like.  A good pH reading for first-morning saliva is in the range of 7 to 7.5.