The kidneys are vital organs that basically filter the blood to make urine. They are responsible for regulating blood volume, mineral balance including calcium, vitamin D synthesis, signaling the bones to make red blood cells, controlling blood pressure and removing waste from blood. Kidney disease, also known as renal disease, causes problems with these functions. Changes in calcium metabolism require appropriate management. Diagnosis and management of kidney disease and calcium disorders require consultation with, and supervision of, a health care professional.
Renal Calcium Regulation
The kidneys filter much of the liquid component of blood, called the serum. Blood serum including calcium enters tubes in the kidneys called nephrons. The nephrons have special channels made from protein that can take calcium in the kidneys and put it back into the blood or allow it to continue into the urine. Parathyroid hormone has several actions, two of which affect the kidneys. First it encourages the kidneys to retain calcium and, therefore, raise the blood levels. Second, it encourages the kidneys to synthesize vitamin D, which takes up calcium from the diet in the intestines. The third function is on bones, where it removes calcium from the bone.
Changes in Calcium with Renal Disease
Calcium may not change at all with mild kidney disease. As kidney disease progresses, however, the kidneys lose their ability to function normally. The protein channels do not return calcium to the blood, and the kidneys do not respond to parathyroid hormone. In addition, vitamin D is not synthesized, so little calcium is absorbed through the GI tract. The result is that calcium levels drop in advanced renal disease.
Consequences
There are a number of consequences from low calcium in renal disease. For one, low calcium levels can lead to muscle and nerve problems. This can manifest as tingling and overly-active muscles and spasms. Since the heart is a muscle and relies on electrical transmission, a loss of calcium, which is an electrically charged mineral, can cause heart disturbances. In addition, because calcium levels are low, the parathyroid gland releases parathyroid hormones in an attempt to raise the calcium. The effect is that more and more calcium is released from bone, causing a loss of bone mass. This is known as renal osteodystrophy.
Treatment
The treatment of low calcium in renal disease involves the administration of calcium and vitamin D. If calcium levels are very low, a health care practitioner may give intravenous calcium. On an ongoing basis, oral calcium and vitamin D are typically given. In addition, other medications will be given to treat other consequences of kidney disease. For example, drugs are given to lower high phosphate levels. In the case of complete kidney failure, dialysis is performed. This procedure involves filtering the blood volume through a machine that acts as an artificial kidney.
References
- "Physiology"; Linda S.Costanzo; 4th Ed 2008
- "Robbins and Cotran Pathologic Basis of Disease"; Vinay Kumar et al.; 8th Ed 2009
- "Harrison's Principles of Internal Medicine"; Anthony S Fauci et al.; 17th Ed 2008
