Measurement
The amount of calcium in blood (more specifically, in blood plasma) can be measured as total calcium, which includes both protein-bound and free calcium. In contrast, ionized calcium is a measure of free calcium. An abnormally high level of calcium in plasma is termed hypercalcemia and an abnormally low level is termed hypocalcemia, with "abnormal" generally referring to levels outside the reference range.
| Target | Lower limit | Upper limit | Unit |
| Ionized calcium | 1.03, 1.10 | 1.23, 1.30 | mmol/L |
| 4.1, 4.4 | 4.9, 5.2 | mg/dL | |
| Total calcium | 2.1, 2.2 | 2.5, 2.6, 2.8 | mmol/L |
| 8.4, 8.5 | 10.2, 10.5 | mg/dL |
The total amount of Ca2+ present in a tissue may be measured using atomic absorption spectrometry, in which the tissue is vaporized and combusted. To measure Ca2+ concentration or spatial distribution within the cell cytoplasm in vivo, a range of fluorescent reporters may be used. These include cell permeable, calcium-binding fluorescent dyes such as Fura-2 or genetically engineered variant of green fluorescent protein (GFP) named Cameleon.
Read more about this topic: Calcium In Biology
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—John Dos Passos (1896–1970)