Less than 1% of the total body phosphorus is in the plasma with 1/3 of this as inorganic phosphate ions, most of which are unbound. Laboratory analysis of serum phosphorus measures all forms of H3PO4 (H3PO4, H2PO4, HPO4) referred to as inorganic phosphate. Serum phosphate levels are higher in serum than plasma due to the clotting process that releases phosphorus from cells and platelets.
Calcium in circulation occurs in three forms: calcium bound to proteins (approximately 40%), calcium complexed to various anions such as citrate and phosphate (8%), and ionized calcium (iCa, approximately 52%. The latter is the biologically active form of calcium and clinically-relevant hypercalcemia only exists when the ionized fraction of calcium is elevated.
A diagnosis of interstitial cystitis in people and cats requires identification of the presence of characteristic (although non-specific) sub-mucosal petechial hemorrhages--referred to as glomerulations--by cystoscopy, though the diagnostic value of this criterion is under debate.