Extracellular and intracellular concentrations – regulated by transport in both directions across cell membranes.
99% is in bone. Metabolism of calcium (Ca) and phosphate (PO4-) is closely related and influenced by circulating levels of parathryoid hormone.
Sources of dietary calcium – milk, cheese, yoghurt, eggs, some shell fish, some nuts, some vegetables
• decrease in total plasma concentration in the presence of normal plasma protein concentration
• varies from a simple biochemical abnormality to severe and life threatening
• due to hypothyroidism, vitamin D deficiency or resistance, renal tubular disease, renal disease, pancreatitis, drugs (eg hypocalcaemic agents)
• symptoms of neuromuscular irritability – muscle cramps in back and leg are common.
• If severe tetany – parathesia of lips, tongue, fingers and feet; carpopedal spasm; general muscle aches.
• Long standing cataracts, dry skin, brittle nails, psoriasis, coarse hair
• increase in total plasma calcium – usually from excessive bone resorption
• due to – hyperparathyroidism (most common), malignancy (next most common), exogenous vitamin D, immobilisation, thyrotoxicosis, sarcoidosis, renal failure
• mild elevations no symptoms (only detected biochemically); significant elevations life threatening emergency
• early symptoms may be subtle changes in ability to concentrate, an increased need for sleep
• other symptoms nausea, vomiting, mental state alterations, constipation, weakness, fatigue, headache, polyuria (from impaired concentrating ability of distal nephron), polydipsia, abdominal pain, increased cardiac repolarisation shorter QT interval on ECG
• Long standing proximal muscle weakness – especially in lower extremities
• treatment – hydration, loop diuretics, dialysis, mobilisation, bisphosphonates, management of underlying cause