Article

Is the Calcium Correct? Measuring Serum Calcium in Dialysis Patients

Division of Nephrology, Department of Medicine, Queen's University, Kingston, Ontario, Canada.
Seminars in Dialysis (Impact Factor: 2.07). 04/2010; 23(3):283-9. DOI: 10.1111/j.1525-139X.2010.00735.x
Source: PubMed

ABSTRACT Abnormalities in calcium concentration are frequent in patients receiving dialysis therapy. Most cases of both hypo- and hypercalcemia are mild and asymptomatic. There is concern, however, that, on the one hand, hypocalcemia can drive hyperparathyroidism and eventually lead to gland hypertrophy and autonomous function. Hypercalcemia, on the other hand, can be associated with increased extraosseous calcium and phosphate deposition leading to vascular calcification with an attendant mortality and morbidity. Calcium exists in three main forms in the blood: the physiologically active free or ionized fraction (terms often used interchangeably), a protein bound fraction, and a fraction complexed to other anions. Although the ionized calcium can readily be measured using ion-specific electrodes, it is the total calcium that is most commonly measured because of sample handling and cost concerns. As it is the free or ionized form that is biologically active (and therefore of most relevance), a number of adjustment formulae have been derived to "correct" the total calcium for changes in albumin, protein, and complexing ion concentrations. These formulae show good statistical correlation with measured ionized calcium in populations studied as a whole, but are generally poor predictors of true ionized hypo- or hypercalcemia in individual patients. International guideline committees in nephrology recommend frequent assessment of calcium levels in dialysis patients and recommend that these levels be kept within the normal reference range. These guidelines are less clear on which measurement of calcium should be used to guide clinical decision making. This review examines the merits of making any adjustment to the total calcium measurement, and suggests when it is appropriate to measure the ionized or free calcium.

1 Follower
 · 
167 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Chronic kidney disease–mineral and bone disorders (CKD-MBD) is a term introduced by the Kidney Disease: Improving Global Outcomes (KDIGO) work group on mineral and bone disorder as a syndrome of interrelated biochemical, bone, and vascular abnormalities encountered in CKD. Biochemical abnormalities in CKD represent primary indicators for the diagnosis and management of CKD-MBD. This review discusses each abnormality separately, with references to both the Kidney Dialysis Outcomes Quality Initiative (KDOQI) Clinical Practice Guidelines for Bone Metabolism and Disease in Chronic Kidney Disease and KDIGO Guidelines for Mineral and Bone Disorder. Selected references to the association between biochemical abnormalities and adverse clinical outcomes in CKD population are provided.
    Clinical Reviews in Bone and Mineral Metabolism 09/2011; 10(3). DOI:10.1007/s12018-011-9122-6
  • [Show abstract] [Hide abstract]
    ABSTRACT: Calcium is the most abundant mineral in the human body. While most of the body's calcium is sequestered in the skeleton, the free, hydrated cation in solution is a key physiologic mediator in a host of metabolic and regulatory processes. The free cation concentration in the extracellular fluid, historically referred to as "ionized calcium" in clinical medicine, is frequently assayed in patients with suspected or known derangements of calcium metabolism. There is controversy in the literature as to whether direct measurement of ionized calcium, measurement of total (free plus chelated or protein-bound) calcium, or adjustment of total calcium for albumin concentration is the best or most practical clinical measure of calcium, as the three methods differ in costs and clinical sensitivities. This manuscript will review calcium biochemistry and homeostasis, compare the utilities of different methods of assessing calcium homeostasis, and discuss appropriate utilization of ionized calcium testing.
    Clinica chimica acta; international journal of clinical chemistry 04/2011; 412(9-10):696-701. DOI:10.1016/j.cca.2011.01.004 · 2.76 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Evaluate whether four different brands/types of heparin coated syringes can represent a source of variability in blood gas analysis (BGA). Blood was collected from one hundred volunteers into different syringes: Syringe I (lithium heparin and calcium balanced); Syringe II: in-house prepared (sodium heparin); Syringe III: (spray-dried calcium-balanced lithium heparin); Syringe IV (lyophilized electrolyte-balanced lithium heparin). Significant differences were as follows: a) Syringe I vs II: pO(2), sO(2), pCO(2)(t), cHCO(3)(-), ctCO(2), base excess (BE), total hemoglobin (tHb), sodium (Na(+)), potassium (K(+)), calcium (Ca(2+)), glucose (Glu), lactate (Lac), O(2) Hb and p 50; b) Syringe I vs III: pH, pO(2), cHCO(3)(-), ctCO(2), BE, Na(+), Glu, Lac and p 50; c) Syringe I vs IV: pH, pO(2), sO(2), pCO(2)(t), BE, Na(+), K(+), Ca(2+), Glu, Lac and O(2) Hb; d) Syringe II vs III: pH, pO(2), sO(2), pCO(2)(t), cHCO(3)(-), ctCO(2), ctO(2), tHb, Na(+), K(+), Ca(2+), Lac and p 50; e) Syringe II vs IV: pH, pO(2), sO(2), pCO(2)(t), cHCO(3)(-), ctCO(2), BE, tHb, Na(+), K(+), Ca(2+), Lac, O(2) Hb and p 50; f) Syringe III vs IV: pH, pO(2), sO(2), cHCO(3)(-), ctCO(2), ctO(2), BE, Na(+), K(+), Ca(2+), O(2) Hb and p 50. The different manufacturers of syringes can represent new source of variability on BGA.
    Clinical biochemistry 03/2012; 45(9):683-7. DOI:10.1016/j.clinbiochem.2012.03.007 · 2.23 Impact Factor