Effect of pH and NaCl on measurements of ionized calcium in matrices of serum and human albumin with a new calcium-selective electrode.

Abstract

A neutral ligand ion-exchanger type of ion-selective electrode is used in the current version of the Orion Model SS-20 calcium analyzer. We evaluated it over the pH range 4.0 to 8.5, using albumin solutions containing 150 mmol/L NaCl and pooled patients' serum. Within this pH range response was nernstian, and the relationship between potential (in millivolts) and log [Ca2+] at each pH was linear. Variation in Ca2+ with increasing ionic strength (because of added NaCl) was not significantly different between standards and albumin solutions; it decreased in both. In contrast, the proportion of calcium in serum increased with increasing NaCl concentrations. Ca2+ was not bound in whole serum albumin at a pH less than about 3.9. We observed a substantial difference between the degree of Ca2+ binding in solutions of fatty-acid-free human albumin and serum.

Comparative Analysis of Whole Blood Ionised Calcium, Lactate and Chloride Concentrations by Gem Premier 3000 and Edan I15 Vet and the Effect of Parity and Postpartum Blood Collection Time on Blood Calcium Status in Holstein With and Without Subclinical Hypocalcemia - Part 1

“…This was probably due to buffering system of the blood in the organism. An increasing H+ concentration decreases calcium binding to albumin or serum proteins which indicate a competitive relationship between H + and Ca 2+ binding (Rehfeld et al 1984). As all other blood gas devices, ICA was displayed as blood pH 7.40 adjusted value (ICA 7.4 ) by both blood gas devices, which was already reported by others to eliminate the effect of small blood pH deviations (Dauth et al 1984 This is not in line with the results of the present study.…”

“…Watson and Anbar 1985;Ballantine and Herbein 1991;Constable et al 2019). A negative correlation between blood ICA concentration and pH was already reported(Rehfeld et al 1984;Goff 2008;Constable et al 2019), which is the basis of the concept for anionic feeding in the close-up of pregnant cows for the stimulation parathormone by decreasing pH and consequently increasing blood calcium concentration by mobilisation from bones. The effect was clinically tested in the urine pH after calving(Goff 2008).…”

“…Screening of blood ICA provides valuable information about physiologically active, free and diffusible forms of calcium, unlike total calcium concentration (TC) (Mahen et al 2018). Blood ICA is primarily dependent on TC, albumin, pH, globulin, chloride, lactate as well as temperature and sodium concentration (Rehfeld et al 1984;Sei et al 2005;Constable et al 2019). The highest effect on the blood ICA is accounted to blood pH, which was already reported in calves (Agnes et al 1993, Constable et al 2019) and in cows (Kvart and Larson 1978).…”

Effects of pH and the plasma or serum concentrations of total calcium, chloride, magnesium,l‐lactate, and albumin on the plasma ionized calcium concentration in calves

“…25 Chloride binding to albumin in human, dog, and rat serum displaces calcium from adjacent electrostatic binding sites, thereby increasing serum cCa 2+ . 8,[26][27][28] Our fifth hypothesis therefore was that hyperchloremia would increase cCa 2+ in calf plasma.…”

“…[2][3][4] The cCa 2+ is also dependent on pH, plasma concentrations of albumin (cAlbumin), globulin (cGlobulin), chloride (cCl), and L-lactate (cL-lactate), as well as the temperature and ionic strength and therefore the plasma concentration of sodium. [5][6][7][8][9] Apart from cTCa, pH is believed to have the largest effect on the cCa 2+ of calf plasma 10 and cow plasma, 11 with log 10 cCa 2+ being negatively and linearly associated with plasma pH. Correction of the measured ionized calcium concentration to pH = 7.40 (cCa 2+ 7.40 ) has been used in experimental studies in cattle to assist in interpretation of measured results relative to a reference range.…”