Calcium ionized

The biosynthesis of PTH and its subsequent secretion are regulated by the plasma ionized calcium (Ca ) concentration through a complex process. An acute decrease of Ca " results in a marked increase of PTH... 

Ionized calcium is an important regulator of a variety of cellular processes, including muscle contraction, stimulus-secretion coupling, the blood clotting cascade, enzyme activity, and membrane excitability. It is also an intracellular messenger of hormone action. 

Figure 4. Effect of pardaxin on intracellular ionized calcium level in bovine adrenal chromaffin cells.

Calcium ion-selective electrodes have recently been commercialized for the measurement of either total or ionized calcium Approximately 45 % of the calcium present in serum is bound to proteins, 5% is complexed to simple anions and 50% exists as the free ion. Traditionally, total calcium measurements have been made by releasing the protein bound fraction. An ion-selective electrode has now allowed the free (ionized) calcium to be measured directly. There has been much debate on the clinical significance of these measurements. The dependence of ionized calcium on pH must be considered. Samples must be either treated anaerobically, tonometered to a constant pH or have a correction factor applied. 

Measure ionized calcium levels (normal 4—5.2 mg/dL or 1-1.3 mmol/L)... 

Check parathyroid hormone (PTH), vitamin D and precursors, magnesium, and phosphate levels ° Pharmacological causes of decreased ionized calcium may include excess infusions of citrate, EDTA, lactate, fluoride poisoning, foscarnet, cinacalcet, bisphosphates, or unrelated increase in serum phosphate or decrease in serum magnesium levels... 

Usually associated with an ionized calcium level of <2.8 mg/dL or 0.7 mmol/L... 

Change to enteral therapy once serum calcium is >8.5 mg/dL or ionized calcium normalizes ° Use cautiously in patients on digitalis glycoside pharmacotherapy... 

Parathyroidectomy is a treatment of last resort for sHPT, but should be considered in patients with persistently elevated iPTH levels above 800 pg/mL (800 ng/L) that is refractory to medical therapy to lower serum calcium and/or phosphorus levels.39 A portion or all of the parathyroid tissue may be removed, and in some cases a portion of the parathyroid tissue may be transplanted into another site, usually the forearm. Bone turnover can be disrupted in patients undergoing parathyroidectomy whereby bone production outweighs bone resorption. The syndrome, known as hungry bone syndrome, is characterized by excessive uptake of calcium, phosphorus, and magnesium for bone production, leading to hypocalcemia, hypophosphatemia, and hypomagnesemia. Serum ionized calcium levels should be monitored frequently (every 4 to 6 hours for the first 48 to 72 hours) in patients receiving a parathyroidectomy. Calcium supplementation is usually necessary, administered IV initially, then orally (with vitamin D supplementation) once normal calcium levels are attained for several weeks to months after the procedure. 

More than 99% of total body calcium is found in bone the remaining less than 1% is in the ECF and ICE Calcium plays a critical role in the transmission of nerve impulses, skeletal muscle contraction, myocardial contractions, maintenance of normal cellular permeability, and the formation of bones and teeth. There is a reciprocal relationship between the serum calcium concentration (normally 8.6 to 10.2 mg/dL [2.15 to 2.55 mmol/L]) and the serum phosphate concentration that is regulated by a complex interaction between parathyroid hormone, vitamin D, and calcitonin. About one-half of the serum calcium is bound to plasma proteins the other half is free ionized calcium. Given that the serum calcium has significant protein binding, the serum calcium concentration must be corrected in patients who have low albumin concentrations (the major serum protein). The most commonly used formula adds 0.8 mg/dL (0.2 mmol/L) of calcium for each gram of albumin deficiency as follows ... 

For acute symptomatic hypocalcemia, 200 to 300 mg of elemental calcium is administered IV and repeated until symptoms are fully controlled. This is achieved by infusing 1 g of calcium chloride or 2 to 3 grams of calcium at a rate no faster than 30 to 60 mg of elemental calcium per minute. More rapid administration is associated with hypotension, bradycardia, or cardiac asystole. Total calcium concentration is commonly monitored in critically ill patients. Under normal circumstances, about half of calcium is loosely bound to serum proteins while the other half is free. Total calcium concentration measures bound and free calcium. Ionized calcium measures free calcium only. Under usual circumstances, a normal calcium level implies a normal free ionized calcium level. Ionized calcium should be obtained in patients with comorbid conditions that would lead to inconsistency between total calcium and free serum calcium (abnormal albumin, protein, or immunoglobulin concentrations). For chronic asymptomatic hypocalcemia, oral calcium supplements are given at doses of 2 to 4 g/day of elemental calcium. Many patients with calcium deficiency have concurrent vitamin D deficiency that must also be corrected in order to restore calcium homeostasis.2,37,38... 

Slightly elevated ionized calcium and LFTs all others WNL. 

Ionized calcium (Ca2+) is the most common signal transduction element in cells [66], Excitable cells, like neurons, contain voltage-dependent Ca2+ channels, which enable these cells to drastically increase cytosolic calcium levels. Rapid fluctuations in presynaptic... 

Clinical chemistry, particularly the determination of the biologically relevant electrolytes in physiological fluids, remains the key area of ISEs application [15], as billions of routine measurements with ISEs are performed each year all over the world [16], The concentration ranges for the most important physiological ions detectable in blood fluids with polymeric ISEs are shown in Table 4.1. Sensors for pH and for ionized calcium, potassium and sodium are approved by the International Federation of Clinical Chemistry (IFCC) and implemented into commercially available clinical analyzers [17], Moreover, magnesium, lithium, and chloride ions are also widely detected by corresponding ISEs in blood liquids, urine, hemodialysis solutions, and elsewhere. Sensors for the determination of physiologically relevant polyions (heparin and protamine), dissolved carbon dioxide, phosphates, and other blood analytes, intensively studied over the years, are on their way to replace less reliable and/or awkward analytical procedures for blood analysis (see below). 

Calcitonin is a polypeptide hormone that (along with PTH and the vitamin D derivative, 1,25-dihydroxycholecalciferol) plays a central role in regulating serum ionized calcium (Ca2+) and inorganic phosphate (Pi) levels. The adult human body contains up to 2 kg of calcium, of which 98 per cent is present in the skeleton (i.e. bone). Up to 85 per cent of the 1 kg of phosphorus present in the body is also found in the skeleton (the so-called mineral fraction of bone is largely composed of Ca3(P04)2, which acts as a body reservoir for both calcium and phosphorus). Calcium concentrations in human serum approximate to 0.1 mg ml-1 and are regulated very tightly (serum phosphate levels are more variable). 

Roy, A.S., V. Taitelman, and S. Bursztein. 1980. Evaluation of the role of ionized calcium in sodium fluoroacetate ( 1080 ) poisoning. Toxicol. Appl. Pharmacol. 56 216-220. 

Serum electrolytes can be altered secondary to respiratory alkalosis. Serum chloride is usually increased serum potassium, phosphorus, and ionized calcium are usually decreased. 

ECF calcium is moderately bound to plasma proteins (46%), primarily albumin. Unbound or ionized calcium is the physiologically active form. 

June, C.H. and Rabinovitch, P.S., Flow cytometric measurement of intracellular ionized calcium in single cells with indo-1 and fluo-3, Methods Cell Biol., 33, 37, 1990. 

One explanation for the adverse effects of excessive phosphorus intakes on bone health of rodents is that of secondary hyperthyroidism (4,j>,6). Under these circumstances, PTH activities and cAMP urinary excretions would be expected to increase and blood serum phosphorus would be expected to increase. This in turn would be expected to result in formation of calcium-phosphorus complexes, decrease in serum ionized calcium, parathyroid stimulation and bone resorption. 

Blood samples were centrifuged at 1000 x g for 20 min at 0-4°. Ionized calcium levels were immediately determined in serum and urine samples using a calcium ion-selective electrode (Ionetics, Inc., Costa Mesa, CA) urine volumes were recorded. The remaining serum and urine were aliquoted for various analyses and stored at -40°. Serum insulin was analysed by radioimmunoassay (Amersham Corp., Arlington Heights, IL). Serum levels of total calcium, phosphorus and creatinine as well as urine creatinine were determined by colorimetric procedures using an automated analyzer (Centrifichem, Baker Instruments Corp., Pleasantville, NY). Glomerular filtration rates (GFR) were calculated from serum and urine creatinine data GFR = urine creatinine/serum creatinine. 

The effects of varying either the calcium or phosphorus level in conjunction with a high beef meal on the urinary calcium excretion of men are shown in Table IV. Urinary calcium excretion (total and ionized) was significantly elevated (P < 0.005) when the high protein beef meal contained 466 mg rather than 166 mg calcium. Increasing the phosphorus level from 308 mg to 700 mg in the high beef meal reduced both total and ionized calcium excretion in the urine, but the response was not statistically significant. Serum levels of calcium (ionized and total) and phosphorus were within normal limits and were unaffected by any of the dietary treatments. 

Results. Table VI gives the serum levels of calcium (total and ionized) and phosphorus. Serum ionized calcium, which ranged from 33% to 36% of total serum calcium, did not respond postprandially to any of the diets consumed. 

Table VII shows the urinary excretion of ionized calcium following the various liquid meals. Urinary excretion of ionized calcium increased during the first hour after ingestion of the basal meal. The excretion rate then decreased and approached fasting levels by 2 hours post-meal. Although the addition of 15 g of protein as cottage cheese increased the quantity of ionized calcium...

Table VII. Postprandial Effects of Protein Level and Source on Urinary Ionized Calcium Excretion in Postmenopausal Women...

Significantly (P < 0.05) greater quantities of ionized calcium were excreted in the urine when the high beef rather than the basal meal was fed. The excretion of ionized calcium following a meal... 

Discussion. In this study of postmenopausal women, serum levels of ionized calcium were unaffected by meal consumption. Levels of total calcium, however, were elevated following meals containing 15 g of protein from either cottage cheese or beef, or 45 g of protein from cottage cheese. Serum total calcium was not affected by diet in the study with men nor in the study reported by Allen et al. using men and women (16). 

Figure 1. Urinary excretion of ionized calcium prior to and following a liquid meal. Key A, 45 g protein, cottage cheese D, 45 g protein, beef O, 45 g protein, soy , no protein.

Figure 8.12 Feedback control of dihydroxy vitamin D3 synthesis by ionized calcium...

Scillitani, A., Guarnieri, V., De Geronimo, S., et al. (2004) Blood ionized calcium is associated with clustered polymorphisms in the carboxyl-terminal tail of the calcium-sensing receptor. J. Clin. Endocrinol. Metab. 89, 5634—5638. 

The most important applications of Ca " ISEs are in biomedical practice, especially in the determination of ionized calcium in serum. A pioneer work in this field was that by Moore [149] (see also [110,111]). At present the Ca ISE is used in the solvent polymeric version in a number of automatic devices for determining ionized calcium in serum, usually with periodic recalibration of the electrode and thermostatting to 37 °C. It should be noted that ISEs measure... 

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