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In a healthy physiology, extracellular calcium levels are maintained within a tight range through the actions of parathyroid hormone, vitamin D and the calcium sensing receptor. [1] Disorders in calcium metabolism can lead to hypocalcemia, decreased plasma levels of calcium or hypercalcemia, elevated plasma calcium levels.
Calcium regulation in the human body. [6]The plasma ionized calcium concentration is regulated within narrow limits (1.3–1.5 mmol/L). This is achieved by both the parafollicular cells of the thyroid gland, and the parathyroid glands constantly sensing (i.e. measuring) the concentration of calcium ions in the blood flowing through them.
The US Institute of Medicine (IOM) established Recommended Dietary Allowances (RDAs) for calcium in 1997 and updated those values in 2011. [6] See table. The European Food Safety Authority (EFSA) uses the term Population Reference Intake (PRIs) instead of RDAs and sets slightly different numbers: ages 4–10 800 mg, ages 11–17 1150 mg, ages 18–24 1000 mg, and >25 years 950 mg. [10]
Normal parathyroid glands measure the ionized calcium (Ca 2+) concentration in the blood and secrete parathyroid hormone accordingly; if the ionized calcium rises above normal, the secretion of PTH is decreased, whereas when the Ca 2+ level falls, parathyroid hormone secretion is increased. [8]
Physiologically, blood calcium is tightly regulated within a narrow range for proper cellular processes. Calcium in the blood exists in three primary states: bound to proteins (mainly albumin), bound to anions such as phosphate and citrate, and as free (unbound) ionized calcium. Only the unbound ionized calcium is physiologically active. Normal ...
Once calcium is confirmed to be elevated, a detailed history taken from the subject, including review of medications, any vitamin supplementations, herbal preparations, and previous calcium values. Chronic elevation of calcium with absent or mild symptoms often points to primary hyperparathyroidism or Familial hypocalciuric hypercalcemia. For ...
Reference ranges (reference intervals) for blood tests are sets of values used by a health professional to interpret a set of medical test results from blood samples. Reference ranges for blood tests are studied within the field of clinical chemistry (also known as "clinical biochemistry", "chemical pathology" or "pure blood chemistry"), the ...
The reference range provided by the particular lab that performed the testing should always be used to interpret the results. [3] Also, some healthy people may have values outside of the "normal" range provided by any lab. [citation needed] Modern analyzers use ion-selective electrodes which give a normal anion gap as <11 mEq/L. Therefore ...