Hypocalcemia pathophysiology
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Manpreet Kaur, MD [2]
Overview
Hypocalcemia may develop in disorders associated with insufficient parathyroid hormone or vitamin D production or resistance to hormonal activities. Perturbations of calcium homeostasis can be caused by environmental factors or occur as a result of genetic mutations in the calcium-sensing receptor (as in type 1 autosomal dominant hypocalcemia), Gs α subunit (as in type 1A and 1B pseudohypoparathyroidism), vitamin D hydroxylase (as in type 1 vitamin D-dependent rickets , and calcitriol receptor (as in type 2 vitamin D-dependent rickets).
Pathophysiology
Physiology
The normal physiology of Hypocalcemia can be understood as follows:[1][2]
- The normal concentrations of calcium in the body is maintained within the narrow range and that is required for the optimal activity of the many extra- and intracellular processes that calcium regulates.
- Calcium transport within the blood is mainly via bound to plasma proteins such as albumin (45%), phosphate and citrate (15%) and ionized state (40%).
- Only the ionized form of calcium is active but most laboratories show report of total serum calcium concentrations.
- The normal concentration of calcium ranges between 8.5 and 10.5 mg/dL.
- The normal range of ionized calcium in the plasma is 4.65 to 5.25 mg/dL.
Pathogenesis
It is understood that hypocalcemia may result through any of the following mechanisms:
Vitamin D deficiency
- One of the common causes of hypocalcemia is underproduction of vitamin D.[3]
- The consequence of low serum calcium levels is an increase in serum PTH (to allow the calcium levels to return within normal range- mainly via increased release of calcium from bone tissue).
- Causes of vitamin D deficiency include:[4]
- Poor intake of vitamin D
- Malabsorption
- Reduced ultraviolet light exposure
- Decrease in 25-hydroxylation to convert vitamin D into 25-hydroxyvitamin D
- Decreased 1-hydroxylation of 25-hydroxyvitamin D (primarily occurrs in the kidney- so chronic kidney disease is one of the causes of reduced active form of vitamin D and hence hypocalcemia)
Hypoalbuminemia
- When there is a fluctuation in serum protein concentrations, especially albumin, total calcium levels in the blood may change.[5][6]
- Whereas the levels of ionized calcium (free form) remains mostly constant, because it is hormonally regulated.
- In cases of hypoalbuminemia, total serum calcium levels may not accurately reflect the physiologically important ionized calcium concentration.
- Therefore, a correction may be required in order to arrive at the corrected calcium levels. (Corrected calcium = Measured calcium + 0.02 x [40 - Albumin])
Hormonal regulation
- Parathyroid hormone (PTH) and vitamin D play an important role in regulating serum calcium.[7]
- Calcium auto-regulates its own serum levels via a calcium-sensing receptor (CaSR) in the parathyroid gland to inhibit parathyroid hormone (PTH) secretion and on a CaSR in the loop of Henle of the kidney to stimulate renal calcium excretion.[8][9][10][11]
- Whenever the serum ionized calcium decreases below normal (even in small amounts) PTH (parathyroid hormone) is secreted to aid in return of serum calcium levels within normal range. This is achieved by 3 major actions of PTH: [12][13][14][15]
- 1)PTH (parathyroid hormone) stimulation of calcium reabsorption in the distal tubule of the kidney results in decreased urinary calcium excretion by the kidney.[16]
- 2)PTH (parathyroid hormone) increases renal production of 1,25-dihydroxyvitamin D which is also called as calcitriol which in turn increases the intestinal calcium absorption.[17]
- 3)PTH (parathyroid hormone) increases bone resorption which in turn increases the serum calcium levels.[18]
- When PTH secretion is insufficient hypokalemia may occur, which is classically seen in hypoparathyroidism.
Magnesium
- Hypocalcemia can be caused by both hypomagnesemia or by severe hypermagnesemia.[19][20]
- Magnesium depletion can lead to hypocalcemia by increasing parathyroid hormone (PTH) resistance.
- Parathyroid hormone (PTH) resistance occurs especially when serum magnesium concentrations fall below 0.8 mEq/L.
- In this patients hypocalcemia can be corrected by only correcting magnesium levels and by not giving calcium.
- Hypomagnesemia can be caused mostly by[21][22]
- Malabsorption
- Chronic alcoholism
- Cisplatin when combined with 5-fluorouracil and leucovorin
- Diuretics
- Aminoglycosides
Acid-base disturbances
Alkalosis
- In alkalosis, hydrogen ions dissociate from the negatively charged albumin, which allows for increased calcium binding and leads to a decreased concentration of free calcium.
- For an increase in pH of 0.1 unit, there is an approximately 0.05 mmol/L (0.1 mEq/L) fall in the serum level of ionized calcium.
Respiratory alkalosis
- Reduced ionized calcium concentration and hypocapnia associated with hyperventilation may contribute to symptoms of vasoconstriction including lightheadedness, fainting, and paresthesia.
Globulin binding
- Calcium binding to globulin is relatively small (1.0 g of globulin binds 0.2–0.3 mg of calcium) and generally does not influence the total serum calcium concentration.[23]
Autoimmune
- Hypoparathyroidism which is acquired but not related to any surgery is most often an autoimmune disease.[24]
- Autoimmune destruction of parathyroid glands results in permanent hypoparathyroidism .
Genetics
The development of hypocalcemia is the result of genetic mutations such as
- Mutations in the transcription factor glial-cell missing B (GCMB).
- Mutations in the calcium-sensing receptor, results in autosomal dominant hypocalcemia (ADH).which is of 2 types[25][26][27]
- Type 1: Autosomal dominant hypocalcemia (ADH) 1 is due to activating mutation in the CaSR.[28][29][30][31]
- Type 2: Autosomal dominant hypocalcemia (ADH) 2 is due to activating mutation in the guanine nucleotide binding protein, alpha 11 gene(GNA11).[32][33]
- This mutation leads to downstream CaSR signaling.
References
- ↑ Fong J, Khan A (February 2012). "Hypocalcemia: updates in diagnosis and management for primary care". Can Fam Physician. 58 (2): 158–62. PMC 3279267. PMID 22439169.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Papapoulos SE, Harinck HI, Bijvoet OL, Gleed JH, Fraher LJ, O'Riordan JL (February 1986). "Effects of decreasing serum calcium on circulating parathyroid hormone and vitamin D metabolites in normocalcaemic and hypercalcaemic patients treated with APD". Bone Miner. 1 (1): 69–78. PMID 3508718.
- ↑ Fong J, Khan A (February 2012). "Hypocalcemia: updates in diagnosis and management for primary care". Can Fam Physician. 58 (2): 158–62. PMC 3279267. PMID 22439169.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Riccardi D, Brown EM (March 2010). "Physiology and pathophysiology of the calcium-sensing receptor in the kidney". Am. J. Physiol. Renal Physiol. 298 (3): F485–99. doi:10.1152/ajprenal.00608.2009. PMC 2838589. PMID 19923405.
- ↑ Goodman WG (January 2004). "Calcium-sensing receptors". Semin. Nephrol. 24 (1): 17–24. PMID 14730506.
- ↑ Quarles LD (July 2003). "Extracellular calcium-sensing receptors in the parathyroid gland, kidney, and other tissues". Curr. Opin. Nephrol. Hypertens. 12 (4): 349–55. doi:10.1097/01.mnh.0000079682.89474.80. PMID 12815330.
- ↑ Toka HR, Pollak MR (September 2014). "The role of the calcium-sensing receptor in disorders of abnormal calcium handling and cardiovascular disease". Curr. Opin. Nephrol. Hypertens. 23 (5): 494–501. doi:10.1097/MNH.0000000000000042. PMID 24992569.
- ↑ Egbuna OI, Brown EM (March 2008). "Hypercalcaemic and hypocalcaemic conditions due to calcium-sensing receptor mutations". Best Pract Res Clin Rheumatol. 22 (1): 129–48. doi:10.1016/j.berh.2007.11.006. PMC 2364635. PMID 18328986.
- ↑ Blaine J, Chonchol M, Levi M (July 2015). "Renal control of calcium, phosphate, and magnesium homeostasis". Clin J Am Soc Nephrol. 10 (7): 1257–72. doi:10.2215/CJN.09750913. PMC 4491294. PMID 25287933.
- ↑ Akerström G, Hellman P, Hessman O, Segersten U, Westin G (April 2005). "Parathyroid glands in calcium regulation and human disease". Ann. N. Y. Acad. Sci. 1040: 53–8. doi:10.1196/annals.1327.005. PMID 15891005.
- ↑ Carroll R, Matfin G (February 2010). "Endocrine and metabolic emergencies: hypocalcaemia". Ther Adv Endocrinol Metab. 1 (1): 29–33. doi:10.1177/2042018810366494. PMC 3474611. PMID 23148147.
- ↑ Carrillo-López N, Fernández-Martín JL, Cannata-Andía JB (2009). "[The role of calcium, calcitriol and their receptors in parathyroid regulation]". Nefrologia (in Spanish; Castilian). 29 (2): 103–8. doi:10.3265/Nefrologia.2009.29.2.5154.en.full. PMID 19396314.
- ↑ Wu X, Sonnenberg H (November 1995). "Effect of renal perfusion pressure on excretion of calcium, magnesium, and phosphate in the rat". Clin. Exp. Hypertens. 17 (8): 1269–85. PMID 8563701.
- ↑ Mortensen L, Hyldstrup L, Charles P (January 1997). "Effect of vitamin D treatment in hypoparathyroid patients: a study on calcium, phosphate and magnesium homeostasis". Eur. J. Endocrinol. 136 (1): 52–60. PMID 9037127.
- ↑ Poole, K; Reeve, J (2005). "Parathyroid hormone — a bone anabolic and catabolic agent". Current Opinion in Pharmacology. 5 (6): 612–617. doi:10.1016/j.coph.2005.07.004. ISSN 1471-4892.
- ↑ Cholst IN, Steinberg SF, Tropper PJ, Fox HE, Segre GV, Bilezikian JP (May 1984). "The influence of hypermagnesemia on serum calcium and parathyroid hormone levels in human subjects". N. Engl. J. Med. 310 (19): 1221–5. doi:10.1056/NEJM198405103101904. PMID 6709029.
- ↑ van den Bergh WM, van de Water JM, Hoff RG, Algra A, Rinkel GJ (2008). "Calcium homeostasis during magnesium treatment in aneurysmal subarachnoid hemorrhage". Neurocrit Care. 8 (3): 413–7. doi:10.1007/s12028-008-9068-9. PMID 18317951.
- ↑ Kido Y, Okamura T, Tomikawa M, Yamamoto M, Shiraishi M, Okada Y, Kimura T, Sugimachi K (October 1996). "Hypocalcemia associated with 5-fluorouracil and low dose leucovorin in patients with advanced colorectal or gastric carcinomas". Cancer. 78 (8): 1794–7. PMID 8859194.
- ↑ Kido Y, Okamura T, Tomikawa M, Yamamoto M, Shiraishi M, Okada Y, Kimura T, Sugimachi K (October 1996). "Hypocalcemia associated with 5-fluorouracil and low dose leucovorin in patients with advanced colorectal or gastric carcinomas". Cancer. 78 (8): 1794–7. PMID 8859194.
- ↑ Taal, Maarten (2012). Brenner & Rector's the kidney. Philadelphia, PA: Elsevier/Saunders. ISBN 978-1416061939.
- ↑ Posillico JT, Wortsman J, Srikanta S, Eisenbarth GS, Mallette LE, Brown EM (October 1986). "Parathyroid cell surface autoantibodies that inhibit parathyroid hormone secretion from dispersed human parathyroid cells". J. Bone Miner. Res. 1 (5): 475–83. doi:10.1002/jbmr.5650010512. PMID 3332555.
- ↑ Baron J, Winer KK, Yanovski JA, Cunningham AW, Laue L, Zimmerman D, Cutler GB (May 1996). "Mutations in the Ca(2+)-sensing receptor gene cause autosomal dominant and sporadic hypoparathyroidism". Hum. Mol. Genet. 5 (5): 601–6. PMID 8733126.
- ↑ Brown EM, MacLeod RJ (January 2001). "Extracellular calcium sensing and extracellular calcium signaling". Physiol. Rev. 81 (1): 239–297. doi:10.1152/physrev.2001.81.1.239. PMID 11152759.
- ↑ Szalat A, Shpitzen S, Tsur A, Zalmon Koren I, Shilo S, Tripto-Shkolnik L, Durst R, Leitersdorf E, Meiner V (March 2017). "Stepwise CaSR, AP2S1, and GNA11 sequencing in patients with suspected familial hypocalciuric hypercalcemia". Endocrine. 55 (3): 741–747. doi:10.1007/s12020-017-1241-5. PMID 28176280.
- ↑ De Luca F, Ray K, Mancilla EE, Fan GF, Winer KK, Gore P, Spiegel AM, Baron J (August 1997). "Sporadic hypoparathyroidism caused by de Novo gain-of-function mutations of the Ca(2+)-sensing receptor". J. Clin. Endocrinol. Metab. 82 (8): 2710–5. doi:10.1210/jcem.82.8.4166. PMID 9253358.
- ↑ Hendy GN, Minutti C, Canaff L, Pidasheva S, Yang B, Nouhi Z, Zimmerman D, Wei C, Cole DE (August 2003). "Recurrent familial hypocalcemia due to germline mosaicism for an activating mutation of the calcium-sensing receptor gene". J. Clin. Endocrinol. Metab. 88 (8): 3674–81. doi:10.1210/jc.2003-030409. PMID 12915654.
- ↑ Lienhardt A, Garabédian M, Bai M, Sinding C, Zhang Z, Lagarde JP, Boulesteix J, Rigaud M, Brown EM, Kottler ML (April 2000). "A large homozygous or heterozygous in-frame deletion within the calcium-sensing receptor's carboxylterminal cytoplasmic tail that causes autosomal dominant hypocalcemia". J. Clin. Endocrinol. Metab. 85 (4): 1695–702. doi:10.1210/jcem.85.4.6570. PMID 10770217.
- ↑ Løvlie R, Eiken HG, Sørheim JI, Boman H (August 1996). "The Ca(2+)-sensing receptor gene (PCAR1) mutation T151M in isolated autosomal dominant hypoparathyroidism". Hum. Genet. 98 (2): 129–33. PMID 8698326.
- ↑ Li D, Opas EE, Tuluc F, Metzger DL, Hou C, Hakonarson H, Levine MA (September 2014). "Autosomal dominant hypoparathyroidism caused by germline mutation in GNA11: phenotypic and molecular characterization". J. Clin. Endocrinol. Metab. 99 (9): E1774–83. doi:10.1210/jc.2014-1029. PMC 4154081. PMID 24823460.
- ↑ Nesbit MA, Hannan FM, Howles SA, Babinsky VN, Head RA, Cranston T, Rust N, Hobbs MR, Heath H, Thakker RV (June 2013). "Mutations affecting G-protein subunit α11 in hypercalcemia and hypocalcemia". N. Engl. J. Med. 368 (26): 2476–2486. doi:10.1056/NEJMoa1300253. PMC 3773604. PMID 23802516.