What is the Purpose of a Calcium Assay in Research?

Calcium signalling is a basic biological process that can be studied in various cells and model organisms. It can help researchers understand physiological processes and the pathogenesis of diseases. It can also help predict the effects of drugs and identify potential side effects. Ideally, a calcium assay will mimic an in-vivo environment.

Ionized calcium

The Ionized Calcium Assay (ICA) is a convenient method for determining calcium in a sample. Its advantages include accurate measurement and a variety of indications.


Calcium assays are fundamental to life sciences research and are crucial for many high-throughput assays in drug discovery. Synthetic calcium indicators have become the gold standard for this purpose due to their high reproducibility, wide dynamic range, and spectral properties. However, genetically encoded calcium indicators (GECIs) are emerging as viable alternatives and are rapidly gaining acceptance in a range of research applications. 

Effects of pH on ionized calcium levels

pH is a major influence on the concentration of free and protein-bound calcium. A rise in pH promotes calcium-albumin complexes, while a fall in pH increases free blood calcium and decreases ionized calcium. Hyperventilation-induced respiratory alkalosis, a process that decreases blood pH, can lower ionized calcium levels.

ISE assessment of total serum calcium

ISE assessment of total serum calcium (TSC) is an important tool for calcium status assessment. It is a highly variable marker that is influenced by many factors, including age, sex, season, and physiological state. Calcium is regulated by vitamin D. Various reference intervals for calcium concentration in serum and plasma have been established.

Payne correction equation

The Payne correction equation for calcium assay in clinical research has a number of limitations. First of all, it does not account for pH, which is an important adjustment variable. Payne calculated the formula based on data from 200 patients, but there was no follow-up study in a second cohort. This meant that the formula was not appropriate for use in the clinical laboratory of a chronic kidney disease population.