Strong ion difference: Inconsistencies lining up.

Abstract

Incongruence between new ideas and current concepts fuels scientific progress. Within acid-balance physiology, an - apparently new - idea of a 'strong ion difference' in plasma (SID) was introduced by Stewart some forty years ago 1-3 . SID is 'the sum of all strong base cation concentrations minus the sum of all strong acid anion concentrations'2 , in clinical practice often ([Na+ ] + [K+ ] - [Cl- ]) in mmol/l. Subsequently, the concept was extended to renal function, and recently this was the focus of an editorial in the journal 4 , henceforth the editorial. The arguments in the editorial are difficult to follow mainly because (i) they seem to violate the fundamental principle of electroneutrality, (ii) they question the mere existence of transmembrane transport of protons and bicarbonate ions, and (iii) they include peculiar cause-effect relationships for which there are little documentation in the literature. These issues will be discussed below, and - as this is difficult without reference to their background - the ideas of Stewart will be commented. The discussion includes numerical examples taken from a quantitative overview (Figure) of essential cause-and-effect relationships representative of a normal person on a typical (H+ generating) Western diet.