Serum calcium, fall

In the absence of PTH (idiopathic or surgical hypoparathyroidism) or an abnormal target tissue response to PTH (pseudohypoparathyroidism), serum calcium falls and serum phosphate rises. In such patients, l,25(OH)2D levels are... 

About 40% of senun calciiun is protein boxmd, with most of it (80%) being bound to albumin. Generally, one or two calcium ions are associated with serum albumin. Albumin serves as a calcium buffer. It can bind more calcium ions when excessive concentrations of calcium appear in the bloodstream. About 13% of the calcium in serum is weakly complexed with phosphate, citrate, and sulfate. About half (47%) of serum calcium occurs as the free calcium ion. The level of free serum Ca is maintained within narrow limits, 1.0 to 1.25 mM (40 to 50 pg/ml). The normal concentration of total serum calcium (boimd plus free) is 85 to 105 pg/ml. Conditions in which the level of free serum calcium falls below and rises above the normal range are called hypocalcemia and hypercalcemia, respectively. The term ionized calcium is often used to refer to the concentrations of free calcium. This term is not scientifically accurate, because all of the calcium in the body is ionized. Calcium does not engage in the formation of covalent bonds (Cotton and Wilkinson, 1966). 

Excess phosphorus in the blood serum, which may result (1) when the kidneys do not excrete phosphorus adequately, or (2) from hypoparathyroidism, which causes an insufficient secretion of parathyroid hormone. When serum phosphorus rises, serum calcium falls, causing tetany. 

As kidney function continues to decline and the GFR falls less than 60 mL/minute/1.73 m2, phosphorus excretion continues to decrease and calcitriol production decreases, causing PTH levels to begin to rise significantly, leading to secondary hyperparathyroidism (sHPT). The excessive production of PTH leads to hyperplasia of the parathyroid glands, which decreases the sensitivity of the parathyroid glands to serum calcium levels and calcitriol feedback, further promoting sHPT. 

Plasma volume and the extracellular fluid space have been observed to constrict 30% during reducing diets (300-600 calories per day) (B22). These changes can be accompanied by functional impairment of glomerular filtration and hepatic perfusion with transient increases up to 2 mg/100 ml in serum creatinine and BSP retention up to 40% (B22). In rare instances a significant fall in serum calcium, magnesium, or potassium was observed. Hyperuricemia was also observed, with concentrations as high as 9 mg/100 ml (B22). 

Aseptic meningitis syndrome-The incidence of this syndrome was 6%. Fever, headache, meningismus, and photophobia were the most commonly reported symptoms a combination of these 4 symptoms occurred in 5% of patients. Headache - Headache is frequently seen after any of the first few doses and may occur in any of the aforementioned neurologic syndromes or by itself. Seizures - Seizures, some accompanied by loss of consciousness or cardiorespiratory arrest, or death, have occurred independently or in conjunction with any of the neurologic syndromes described below. Patients predisposed to seizures may include those with the following conditions Acute tubular necrosis/uremia fever infection a precipitous fall in serum calcium fluid overload hypertension hypoglycemia, history of seizures and electrolyte imbalances those who are taking a medication concomitantly that may, by itself, cause seizures. 

Osteomalacia is the condition in which bone becomes demineralised due to deficiency of vitamin D. In this condition parathyroid hormone (PTH) acts on the bone to maintain serum calcium, resulting in demineralisation. Serum calcium is usually normal or slightly low alkaline phosphatase levels are high, reflecting excessive osteoblast activity, and serum phosphate falls as an effect of PTH on the kidney. The same condition in children results in defects in long bone formation, and is termed rickets. 

Alternatively, ionized calcium can be estimated using the following rule Total serum calcium will fall by 0,8 mg/dl for each 1,0 g/dl decrease in serum albumin concentration... 

Shackney S, Hasson J. Precipitious fall in serum calcium hypotension and acute renal failure after IY phosphate treatment of hypercalcemia. Arch Intern Med 1968 122 150. 

The time of year and the point during the menstrual cycle during which vitamin D derivatives are measured may be important. In seven women there was a two-fold rise in the serum concentration of 1,25-dihydroxycolecalci-ferol on day 15 of the menstrual cycle compared with days 1 and 8, without a detectable change in the serum calcium concentration (187). This increase did not occur in five women taking oral contraceptives, and there was a small but significant fall in the serum calcium concentration. 

Morgan et al. (M3) examined the effect of the administration of EDTA in idiopathic hypercalcemia. Given orally, a dosage of up to 3 g daily resulted in a fall in the serum calcium level. Given subcutaneously in a dosage of 1 g daily, there was a fall in calcium retention in a balance study, a retention of 51 % being converted to a retention of 28 % on similar dietary intakes of calcium. There was an increase in the urinary excretion of calcium. 

Bisphosphonates (see later). Pamidronate is infused according to the schedule in Table 38.1 it is active in a wide variety of hypercalcaemic disorders. Fall in serum calcium begins in 1-2 d, reaches a nadir in 5-6 d and lasts 20-30 d. Etidronate may be given i.v. in hypercalcaemia of malignant disease. It acts in 1-2 d and a dose lasts 3 weeks it may also provide benefit for neoplastic metastatic disease in bone. Clodronate (oral or i.v.) or zoledonic acid (i.v) are alternatives. 

The overall effect in most animals is to stimulate intestinal absorption of calcium with a concomitant increase in serum calcium and a reduction in parathyroid hormone (PTH). Modest hypercalcemia allows the glomerular filtration rate to remain stable and hypercalciuria to occur because of increased filtered load of calcium and reduction of tubular resorption of calcium with reduced PTH. However, with further increases in serum calcium, the glomerular filtration rate decreases, resulting in an even more rapid increase in serum calcium and the subsequent fall in urinary calcium. 

A fall in serum calcium has been reported with atenolol... 

Shackney S, Hasson J. Preciptious Fall In Serum Calcium, Hypotension, and Acute Renal Failure After Intravenous Phosphate Therapy for Hypercalcemia. Ann of Intern Med 1967 5 906-16. 

Regulation of serum calcium (see Chapter 49) The Calcium-sensing receptor (CaSR) on the parathyroid gland recognizes the ambient concentration of ionized calcium, which in turn regulates synthesis and secretion of PTH. When ionized calcium concentrations fall... 

Clinically, hypocalcemia most commonly presents with neuromuscular hyperexcitability, such as tetany, paresthesia, and seizures. A rapid fall in the serum calcium also may be associated with hypotension and electrocardiographic abnormalities. 

Laboratory findings in rickets and osteomalacia include an increased serum ALP, with other alterations in bone and mineral metabolism dependent on the cause and severity of the disorder. ALP is usually increased because of the increased osteoblastic activity associated with producing unmineralized osteoid. Calcium may be low-normal or low in vitamin D deficiency depending on the severity of the disease. Phosphate may be normal or low, but falls with the development of secondary hyperparathyroidism. The serum calcium and PTH concentrations are usually normal in renal tubular defects of phosphate transport. Vitamin D nutrition may be assessed by the determination of serum 25(OH)D. Renal phosphate defects can be best assessed by determination of the renal phosphate threshold. 

Mithramycin (plicamycin) is a potent cytotoxic antibiotic that inhibits osteoclast-mediated bone resorption and thereby reduces hypercalcemia. Mithramycin may be administered at a dose of 25 mcg/kg via intravenous infusion over 4 to 6 hours in saline or 5% dextrose solutions. This therapy may be repeated daily for 3 to 4 days or on alternating days for 3 to 8 doses. ° Serum calcium levels begin to fall within 12 hours of a mithramycin dose, with the peak effect generally occurring within 48 to 96 hours.Single doses are usually well tolerated. Adverse effects of mithramycin include nausea, vomiting, stomatitis, thrombocytopenia, inhibition of platelet function, and renal and hepatotoxicity. Because these adverse effects are more commonly associated with multiple doses, mithramycin is usually limited to short-term therapy in patients who have not responded to alternative therapies. Monitoring parameters include complete blood count, liver function, and renal function. Mithramycin should be avoided in patients with thrombocytopenia and liver and renal insufficiency. ... 

A symptomatic rapid fall in serum calcium concentrations (often to values <7 mg/dL) is common in patients who have had a parathyroidectomy or thyroidectomy. Hypocalcemia in these postsurgical patients is generally transient in nature. " The hungry bone syndrome is a condition of profound hypocalcemia whereby the bone avidly in-... 

Kozeny [47] evaluated IL-2 associated fluid and electrolyte disorders in 8 patients with metastatic cancer. All patients developed capillary leak syndrome, prerenal azotemia, hypophosphatemia, hypocalcemia, hypomagnesemia, and respiratory alkalosis. As noted in other studies, albumin fell precipitously with an associated fall in serum calcium. However, measurement... 

The fall in serum calcium which follows parathyroidectomy is associated with a rise in calcium excretion (T1). Taken in conjunction with the hypocalcemic hypercalcuria of clinical hypoparathyroidism (L5), this suggests that the apparent calcuric effect of parathyroid extract is simply a reflection of its calcemic action. In fact, administration of the hormone appears if anything to reduce urinary calcium. Evidence to this effect has been produced by Bernstein et al. (B6), who have demonstrated a steep rise in calcium/inulin clearance ratio in dogs after parathyroidectomy... 

In severe osteomalacia due to vitamin D deficiency, serum calcium will fall, and there will be an appropriate increase in PTH secretion. Serum alkaline phosphatase activity will also be elevated. 

An example of a control chart is illustrated in Figure 3.6, representing a plot of day-to-day results of the analysis of a pooled serum calcium or a control sample that is run randomly and blindly with samples each day. A useful inner control limit is two standard deviations since there is only 1 chance in 20 that an individual measurement will exceed this purely by chance. This might represent a warning limit. The outer limit might be 2.5 or 3cr, in which case there is only 1 chance in 100 or 1 chance in 500 a measurement will fall outside this range in the absence of systematic error. Usually, one control is run with each batch of samples (e.g., 20 samples), so several control points may be obtained each day. The mean of these may be plotted each day. The random scatter of this would be expected to be smaller by VA, compared to individual points. 

The principal adverse effect of cinacalcet is hypocalcemia. The drug should not be used if the initial serum calcium is <8.4 mg/dL serum calcium and phosphate concentrations should be measured within one week and PTH should be measured within 4 weeks of therapy initiation. Adynamic bone disease may develop in patients with secondary hyperparathyroidism, so the drug should be discontinued or the dose decreased if the PTH level falls below 150 pg/mL. 

The maximum recommended dose for the treatment of hypercalcemia of malignancy is 4 mg. A clinically significant deterioration in renal function occurs when single doses of this agent exceed 4 mg and the infusion duration is less than 15 minutes (52). It is recommended that patients be well hydrated before infusion. If serum calcium levels do not fall to normal levels, retreatment is appropriate, but retreatment is not recommended until 7 days have elapsed from the initial treatment. For the treatment of multiple myeloma and metastatic bone lesions, a 4-mg initial dose is recommended, followed by additional doses every 3 to 4 weeks for 9 to 15 months (prostate cancer, 15 months breast cancer, 12 months other solid tumors, 9 months). 

Hypocalcemia occurs when a serum calcium level falls below 4.5 mEq/L therefore, the nurse would not question administering this medication to the client whose serum calcium level is low. 

All these processes are dependent on an adequate supply of calcium from the diet. It is the integrated action of parathyroid hormone and vitamin D3 which supplies the required amounts of calcium for all these processes via a smoothly operating calcium homeostatic mechanism. When serum calcium concentration falls below 10 mg/100 ml, the sequence of events shown in Fig. 2 takes place. 

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