Calcium – Serum Blood Test
The human organism contains about 1 kg of calcium, more than 99% is stored as hydroxyapatite in the bone. The total calcium in the serum consists of free ionized calcium (50%), of protein bound calcium (40%) and calcium in the form of inorganic complexes (10%, e.g. with phosphate). Calcium is a very important electrolyte for electromechanical coupling within the action potential of muscle cells. Furthermore, it has significance in signal transduction, bone strength, blood clotting, hormone secretion and in the immune system.
Total calcium 2,1–2,6 mmol/l, free calcium 1,15–1.35 mmol/l.
Laboratory test method:
Measurement of free calcium with ion-selective electrode. Measurement of total calcium with flame photometer or atomic absorption spectroscopy.
Measurement of calcium in serum is indicated in nephrolithiasis, hyperparathyroidism, bone metastases or other bone diseases, renal cell carcinoma, chronic renal insufficiency or acute pancreatitis.
Differential Diagnosis of Hypocalcemia:
Hypocalcemia is a low concentration of calcium in the blood. Mild hypocalcemia causes no symptoms, severe hypocalcemia leads to paresthesia, muscle spasms, seizures, confusion, or cardiac arrhythmia. Causes are Vitamin D deficiency (malnutrition, malabsorption, disturbed liver or kidney hydroxylation), protein deficiency, hypoparathyroidism, pseudohypoparathyroidism, osteoplastic bone metastases, medullary thyroid carcinoma, hyperphosphatemia (tumor lysis, renal insufficiency), complication of acute pancreatitis, hepatotoxic drugs. The (respiratory) alkalosis leads to a lack of free ionized calcium.
Differential Diagnosis of Hypercalcemia:
Hypercalcemia is a high concentration of calcium in the blood. Mild hypercalcemia causes no symptoms, severe hypercalcemia leads to weakness, kidney stones, confusion, depression, or coma. Causes are primary hyperparathyroidism, hyperthyroidism, pheochromocytoma, osteolytic bone metastases, paraneoplastic (e.g. renal cell carcinoma), overdose with vitamin A or D, medications (thiazides, lithium), sarcoidosis, tuberculosis, immobilization, renal insufficiency.
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- Guder, W. G. & Nolte, J.
- Das Laborbuch für
Klinik und Praxis
Urban + Fischer, 2009
Siegenthaler 1988 SIEGENTHALER, W. ;
SIEGENTHALER, W. (Hrsg.):
- Differentialdiagnose innerer Krankheiten.
Georg Thieme Verlag, Stuttgart, New York., 1988