Serum total calcium

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). 

Patients randomly assigned to PTH g4 at doses of 50 micrograms/day (n = 50), 75 micrograms/day (n = 52), 100 micrograms/day (n = 51), or to placebo (n = 53) had a dose-related increase in serum total calcium concentrations. This effect was most evident in the first 6 months and appeared to improve at 6—12 months. There was transient hypercalcemia in 24 patients, of whom 11 were taking 100 micrograms/day (17). 

The results of the laboratory analyses are summarized in Table 30-1. The serum total calcium concentration was low (7.9 mg/dL normal... 

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. 

If the increase in pH is great enough, increased neuromuscular activity may be seen, and above pH 7.55, tetany may develop even in the presence of a normal serum total calcium concentration. The cause of the tetany is a decreased concentration of ionized calcium due to increased binding of calcium ions by protein (mainly albumin) and other anions. Measurement of CL status can be helpful, as causes of metabolic alkalosis fall into Cfr responsive, CL resistant, and exogenous base categories (Box 46-1 see also Figure 46-4). 

Thode J, Juul-Jorgensen B, Bhatia HM, Kjaerulf-Nielsen M, Bartels PD, Fogh-Andersen N, Siggaard-Andersen O. Comparison of serum total calcium, albumin-corrected total calcium and ionized calcium in 1213 patients with suspected calcium disorders. Scand J Clin Lab Invest 1989 49 217-23. 

Schenck, P. A., and D. J. Chew. 2005. Prediction of serum ionized calcium concentration hy use of serum total calcium in dogs. American Journal of Veterinary Research 66 1330-1336. 

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

Reference Intervals. Plasma or serum total calcium concentrations vary with age. Premature infants tend to exhibit hypocalcemia whereas full-term neonates have higher levels than adults. The 95% confidence range in children, ages 4-20 years, is 2.30-2.75 mmol/liter [16-18]. The mean adult total calcium concentration is 2.35 mmol/liter with 95% confidence range from 2.20 to 2.55 mmol/liter. Five percent lower means have been reported for persons over 50 years [19]. The quoted reference intervals should be taken as an indication of expected values but each laboratory should establish its own reference intervals depending on the assay method and the population of interest. 

Pybus, J. Feldman, F. J. and Bowers, 6. N., Jr. Measurement of total calcium in serum by atomic absorption spectrophotmetry with use of a strontiim internal reference. Clin. Chem. (1970), lj6, 998 - 1007. 

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. 

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... 

Because the severity of symptoms and the absolute serum concentration are poorly correlated in some patients, institution of therapy should be dictated by the clinical scenario. All patients with hypercalcemia should be treated with aggressive rehydration normal saline at 200 to 300 mL/hour is a routine initial fluid prescription. For patients with mild hypocalcemia, hydration alone may provide adequate therapy. The moderate and severe forms of hypercalcemia are more likely to have significant manifestations and require prompt initiation of additional therapy. These patients may present with anorexia, confusion, and/or cardiac manifestations (bradycardia and arrhythmias with ECG changes). Total calcium concentrations greater than 13 mg/dL (3.25 mmol/L) are particularly worrisome, as these levels can unexpectedly precipitate acute renal failure, ventricular arrhythmias, and sudden death. 

P. Anker, E. Wieland, D. Ammann, R.E. Dohner, R. Asper, and W. Simon, Neutral carrier based ion-selective electrode for the determination of total calcium in blood-serum. Anal. Chem. 53, 1970-1974... 

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. 

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. 

The hamster is susceptible to atherosclerosis. Nistor et al. (1987) fed male hamsters a hyperlipidemic diet consisting of standard chow supplemented with 3 % cholesterol and 15 % commercial butter for 12 months. Serum total cholesterol doubled after 3 weeks and attained a 17-fold value after 10 months. Up to 6 months, smooth muscle cells in the intima and media of the aorta as well as endothelial cells began to load with lipids. After 10 months the affected zones looked like human atherosclerotic plaque with huge cholesterol crystal deposits, calcium deposits and necrosis. 

In patients with ulcerative cohtis, Boswellia serrata 350 mg tds for 6 weeks produced improvements in stool properties, histopathology of rectal biopsies, hemoglobin, serum iron, calcium, phosphorus, proteins, and total leukocyte and eosinophil counts, with remission in 82% of patients (3). The corresponding figure with sulfasalazine 1 g tds was 75%. 

Brett, E.M. and Hicks, J.M. (1981). Total-calcium measurement in serum from neonates Limitations of current methods. Clin. Chem. 27, 1733-1737. 

E520 Gawoski, J.M. and Walsh, D. (1989). Citrate interference in assays of total calcium in serum. Clin. Chem. 35, 2140-2141. 

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). 

Figure 49-2 Equilibria and determinations of calcium in serum. Calcium can move among three physiochemical pools (1) free calcium, (2) protein-bound calcium, and (3) calcium complexed with inorganic and organic anions. Methods for determining total calcium measure all three pools, whereas methods for determining free calcium measure only that pool.

An unusual and treatment-resistant form of symptomatic hypocalcemia is seen in patients treated with large amounts of burn cream that contains polyethylene glycols. The glycols are absorbed and metabolized to dicarboxylic adds that bind calcium. Patients develop markedly increased total calcium and decreased free calcium, along with a metabolic acidosis and increased serum osmolality from the glycols. 

Primary hyperparathyroidism is diagnosed by laboratory studies. Hypercalcemia should be documented by measuring total calcium and serum albumin, or ideally free calcium, on more than one occasion before initiating further testing. Measurement of intact PTH (with concomitant measurement of calcium) is the most sensitive and specific test for parathyroid function and is central to the differential diagnosis of hypercalcemia. Serum l,25(OH)2D is usually in the upper half of the reference interval or increased in primary hyperparathyroidism, as PTH stimulates its production. By contrast, l,25(OH)2D (lilte PTH) is. low-normal or suppressed in nonparathyroid hypercalcemia, except in sarcoidosis, other granulomatous diseases, and certain... 

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... 

Many methods have been used historically to measure total Today, only photometric, ISE, and occasionally atomic absorption spectrophotometry methods are routinely used by clinical laboratories for the measurement of serum and urine total calcium. According to the College of American Pathologists Comprehensive Chemistry Survey,... 

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

Atomic Absorption Spectrometry Methods The National Committee for Clinical Laboratory Standards (NCCLS) has approved a method using atomic absorption spectrophotometry (AAS) as a reference method for measuring total serum calcium. This method has been compared with isotope dilution-mass spectrometry (ID-MS), the definitive method for total serum calcium developed by the National Institute of Standards and Technology. The reference method is reported to have an accuracy of 100 2%, compared with 100 0.2% for ID-MS. Although AAS can provide better accuracy and precision for total serum calcium than the widely used photometric methods, it is used by only a few laboratories. It should continue to be used for validating new total calcium methods. 

The effect of the three major cations. Nab Kb and Mg b is offset by their inclusion in calibrators at normal serum concentrations. An automated diluter is recommended because the imprecision (expressed as the coefficient of variation [CV]) for measurements of total calcium should be less than 1.5% and preferably less than 1%. A serum-based calibrator with calcium concentration determined by ID-MS is available commercially. 

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