In chemistry, Titratable acid generally refers to any acid that can lose proton(s) in an acid-base reaction.
The term is sometimes used slightly differently in other fields. For example, in renal physiology, Titratable acid is a term to describe acids such as phosphoric acid, sulfuric acid which are involved in renal physiology. It is used to explicitly exclude ammonium (NH4+) as a source of acid, and is part of the calculation for net acid excretion.
See also 
- Physiology at MCG 7/7ch12/7ch12p27 - "Regeneration of Bicarbonate, the Role of Titratable Acid: Definition of Titratable Acid"