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Operator’s Manual – OPTI CCA-TS2 Ca-1
ANALYTES CALCIUM
Ionized Calcium (Ca
++
)
Clinical Significance
1
Calcium in blood is distributed as free calcium ions (50%); bound to protein, mostly albumin (40%); and
10% bound to anions such as bicarbonate, citrate, phosphate and lactate. However, only ionized calcium
can be used by the body in such vital processes as muscular contraction, cardiac function, transmission of
nerve impulses and blood clotting. The OPTI CCA-TS2 measures the ionized portion of the total calcium.
In certain disorders such as pancreatitis and hyperparathyroidism, ionized calcium is a better indicator for
diagnosis than total calcium.
Elevated calcium,
hypercalcemia , may be present in various types of malignancy, and calcium
measurements may serve as biochemical markers. In general, while ionized calcium may be slightly more
sensitive, either ionized or total calcium measurements have about equal utility in the detection of occult
malignancy. Hypercalcemia occurs commonly in critically ill patients with abnormalities in acid-base
regulation and losses of protein and albumin, which gives a clear advantage to monitoring calcium status
by ionized calcium measurements.
Decreased calcium, hypocalcemia, is found in patients with decreased intestinal absorption, increased
renal elimination, increased deposition of calcium in the bones, increased binding to proteins when the pH
increases or binding to citrate, and hypoparathyroidism.
Patients with renal disease caused by glomerular failure often have altered concentrations of calcium,
phosphate, albumin, magnesium and pH. Since these conditions tend to change ionized calcium
independently of total calcium, ionized calcium is the preferred method of accurately monitoring calcium
status in renal disease 2 .
Ionized calcium is important for diagnosis or monitoring of: hypertension management, parathyroidism,
renal diseases, malnutrition, kidney stones, multiple myeloma and diabetes mellitus.
Ionized calcium may be reported either as the actual ionized calcium, referred to actual pH of the patients,
or as normalized ionized calcium, to a standard pH at pH 7.40. The binding of calcium by protein and
small anions is influenced by pH and because of this relationship specimens should be analyzed at the pH
of the patient’s blood.
Measurement Principle
The Ca
++
ion optodes are closely related to the more familiar Ion Selective Electrodes (ISEs).
The optodes use ion selective recognition elements (ionophores) similar to those used in ISEs, however
the ionophores are linked to fluorescent dyes instead of electrodes. These types of dyes have been
used since the 1970’s to visualize and quantify cellular ion levels in fluorescence microscopy and cell
counters 3
.
As the ion concentration increases, these ionophores bind larger amounts of ions and cause the
fluorescence intensity to increase or decrease, depending on the particular ion. Like the pH optode, the
ion optodes do not need a reference electrode, however, several of them do exhibit a small pH sensitivity
which is automatically compensated in the OPTI CCA-TS2 using the measured pH.