Total calcium plasma

CalcitrioPs action primary function is in regulating plasma calcium concentration. In health, the plasma total calcium concentration is tightly controlled at 2.35-2.55 mmol/1. Only the ionized or free fraction, amounting to about 50% of the total, is physiologically active in for example, maintenance of membrane electrical potential and bone formation. The hormone causes increased bone resorption via activation of osteoclasts (see Section 9.4) and increased intestinal absorption of calcium following the synthesis of a specific binding protein in mucosal cells. As described in Section 4.7, some... 

Reference intervals for Total and Free Calcium IN Serum and Plasma Total Calcium... 

As in the case with abnormalities of glucose and electrolyte metabolism, all of the above disorders of mineral metabolism can be avoided if the physician is fully aware of the specific mineral composition of the infusate and if a careful monitoring schedule for plasma total calcium, inorganic phosphate and magnesium is adhered to. 

Of the plasma total concentration of calcium (around 2.5 mmol/1), approximately half is bound to albumin. The unbound fraction is physiologically active in roles such as clotting, in regulating neuromuscular membrane potential and of course for bone formation. There exists an equilibrium between the bound and free fractions, so the albumin can be seen as a buffer able to release or take up calcium as circumstances... 

When compared with 12 healthy matched controls, 13 women who had taken lithium for a mean of 8 (range 3-16) years had higher mean ionized and total calcium concentrations, but mean plasma parathormone concentrations did not differ. In eight of the women taking lithium, the calcium concentration was above the upper end of the reference range, and in one the parathormone concentration was abnormally high (661). 

Approximately 50% of the total calcium in plasma is either bound to albumin or complexed to small ligands. The remaining ionized fraction is the biologically active form. Whenever... 

With prolonged bed rest, fluid retention occurs and plasma protein and albumin concentrations may be decreased by an average of 0.5 and 0.3g/dL, respectively. The concentrations of protein-bound constituents are also reduced, although mobilization of calcium from bones with an increased free ionized fraction compensates for the reduced protein-bound calcium, so serum total calcium is less affected. Serum aspartate aminotransferase activity is usually slightly less in individuals confined to bed than in those undertaking normal physical activity. Initially and paradoxically, creatine kinase (CK) activity is increased as a result of its release from skeletal muscles, but ultimately, CK activity may be less than in active, healthy individuals. Serum potassium may be reduced by up to 0.5mmol/L because of reduction of skeletal muscle mass. 

Any increase in the concentration of one anion is accompanied either by a corresponding decrease in other anions or by an increase in one or more cations or both, so total electrical neutrality is invariably maintained. Similarly, any decrease in the concentration of anions involves either a corresponding increase in other anions, or a decrease in cations, or both. In the case of polyvalent ions (e.g., Ca or Mg ), it is important to distinguish between the substance concentration of the ion itself and the concentration of the ion charge. Thus although the concentration of total calcium ions in normal plasma is 2.5 mmol/L> the concentration of the total calcium ion charge is 5.0 mmol/L (also called 5 mil-liequivalents per liter [mEq/L]). This law of electrical neutrality should not be confused with acid-base neutrality (pH = 7.0, where the activity of H" " equals the activity of OH"). 

Calcium can be redistributed among the three plasma pools, acutely or chronically, by alterations in the concentration of protein and small anions, changes in pH, or changes in the quantities of free calcium and total calcium in the serum (Figure 49-2). 

The methods most widely used for quantifying calcium measure either free (ionized) calcium or total calcium. The term ionized calcium is a misnomer because all plasma or serum calcium is ionized whether or not it is associated with protein or small anions by ionic binding. Throughout this... 

Adjusted calcium is calculated from total calcium and albumin by first calculating a correction factor by multiplying the deviation of plasma albumin from the mean of its reference interval by the slope of the regression of total calcium against albumin. The following equation is often seen in textbooks, but fads to consider the lack of harmonization of albumin and calcium methods, and differences in patient populations ... 

Photometric and atomic absorption spectrophotometric methods for measuring the total calcium in serum and plasma are described and discussed below. 

Robertson WG, Marshall RW. Calcium measurements in serum and plasma total and ionized. CRC Crit Rev Clin Lab Sci 1979 11 271-304. 

Extracellularly, calcium ions circulate in the blood plasma and interstitial fluid (Sect. 3.3.1). In blood plasma, calcium ions are chelated to albumin and citrate. Albumin (mol. wt. 66,700 kDa) is present at 50-60 mg/mL in plasma, corresponding to 0.9 m mol/L. Although plasma albumin has many different sites that can chelate calcium ions in vitro, only one site binds to calcium ions at physiological albumin concentrations and pH. Thus, albumin binds 0.9 mmol/L of free plasma Ca2+. In addition, citrate (Fig. 10.7), a tricarboxylic acid that the liver secretes into plasma, chelates a free calcium ion to two of its three carboxyl groups, replacing two Na+ ions. Citrate has a molar concentration of 0.08 mM in venous blood and therefore binds to an equivalent concentration of free calcium. Because the total calcium ion concentration of venous blood is 1.14 mmol/L (range 0.2), and the free calcium ion concentration is 0.1 mM, it appears that 0.15 mM of the plasma calcium ion concentration is bound to other plasma components. 

The disorders of calcium homeostasis are related to the calcium content of the extracellular fluid, which contains less than 0.5% of the total body stores of calcium. Skeletal bone contains more than 99% of total body stores of calcium. ECF calcium is moderately bound to plasma proteins (46%), primarily albumin. Unbound or ionized calcium is the physiologically active form and is the fraction that is homeostatically regulated. Extracellular calcium, however, is most commonly measured as the total serum calcium level, which includes both bound and unbound calcium. The normal total calcium serum concentration range is 8.5 to 10.5 mg/dL. °... 

Unbound calcium is the biologically active fraction of the total calcium in plasma and maintenance of its concentration within tight limits is required for nerve function, membrane pcmieability, muscle contraction and glandular secretion. It is the unbound calcium concentration W hich is recognized by the parathyroid glands, and PTH acts to keep this concentration constant. 

Laboratory and Exercise Evaluation Laboratory evaluations performed at each two-week visit included plasma total cholesterol, LDL-C, HDL-C, VLDL-C, and plasma total triglycerides.23 The lipoprotein determinations, LDL-C, HDL-C, and VLDL-C were not performed at Week 16. White blood cell counts, calcium, and serum glutamic oxaloacetic-transaminase (SGOT) were done before and after feeding LBG products. Weight was recorded at each visit. 

The influence of hormones, drugs and miscellaneous compounds on serum and plasma ionised calcium has also been investigated [70,107,119,120,125]. The Orion 99-20 flow-through model calcium ion-selective electrode is especially suitable for this purpose in anaesthetised patients and animals. Twice-daily doses (50 mg) of hydrochlorothiazide for 25 days administered to 9 normal human subjects significantly raised total and ionic calcium levels. The effect lasted for a... 

Venous stasis and erect posture can elevate both plasma and serum total calcium by 0.1-0.15 mmol/liter [15]. 

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