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Corrected Calcium for Serum Albumin

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Corrected calcium = serum calcium + 0.8 (4 - serum albumin)
Patient's measured total calcium:
Patient's serum albumin level:  


Normal laboratory values (adult patients):
Calcium (Serum):  8.5 - 10.5 mg/dL (2.12 - 2.57 mmol/L )
Calcium (Ionized) Serum:   4.5 - 5.6 mg/dL (1.1-1.4 mmol/L)

Body Calcium:
99% in bone.
1% in ECF:
[50% in its free ionized form]
[40% complexed with albumin]
[10% complexed with anions such as phosphate.]

Less than 1% of the body's calcium is contained within the ECF, yet this concentration is regulated carefully by the parathyroid hormone and calcitonin.  Parathyroid hormone is released by the parathyroid gland in response to a low serum calcium level. It increases resorption of bone (movement of Ca++ and PO4 out of the bone); activates vitamin D, which increases the absorption of calcium from the GIT; and simultaneously stimulates the kidneys to conserve calcium and excrete phosphorus.  Calcitonin is produced by the thyroid gland when serum calcium levels are elevated (inhibits bone resorption). 

      The ECF gains Ca++ from intestinal absorption and resorption from bones.  It is lost from the ECF via secretion into the GIT, urinary excretion, and deposition into bone.

      Calcium is present in 3 different forms in the plasma: ionized, bound and complexed. Only the ionized calcium is physiologically important.  The percentage of calcium that is ionized is affected by pH, phosphorus, and albumin levels.  The relationship between ionized calcium and plasma pH is reciprocal (increase in pH decreases percent of Ca++ ionized). Patients with alkalosis for example may show signs of hypocalcemia despite a normal total calcium level.  Changes in albumin will affect total serum calcium without changing the level of free calcium. (decreased albumin --> decreased total Ca++ --> constant free Ca++)


Signs and symptoms
arrowNumbness with tingling of fingers, extremities and circumoral region 
arrowhyperactive reflexes, 
arrowmuscle cramps,  
arrowcarpopedal spasm,
arrow stridor, 
arrowPositive Trousseau's sign (carpal spasm with BP cuff) and positive Chvostek's sign (contraction of facial and eyelid muscles when facial nerve tapped).  Cardiac effects include decreased myocardial contractility and heart failure.

History and risk factors:
1) Decreased ionized calcium: alkalosis; administration of large quantities of citrated blood (may bind calcium); hemodilution (volume replacement etc.)
2) Increased calcium loss in body fluids:  certain diuretics.
3Decreased intestinal absorption: decreased intake; impaired vitamin D metabolism (renal failure); chronic diarrhea, post-gastrectomy.
4) Hypoparathyroidism: congenital or acquired.
5) Hyperphosphatemia: e.g. renal failure. When hypocalcemia persists, it is best to delay calcium supplementation until the serum phosphate level is below 6 mg/dL to reduce the risk of metastatic calcification.
6) Hypomagnesemia (decreased PTH action and release).  Chronic alcoholism; acute pancreatitis.  Hypocalcemia is difficult to correct without first normalizing the serum magnesium concentration.

Diagnostic tests:
-Total serum calcium may be less than 8.5 mg/dl.  Serum  calcium levels should be evaluated with serum albumin.  For every 1.0 mg/dL drop in serum albumin, there is a 0.8 - 1.0 mg/dL drop in the total calcium level.
-Ionized calcium will be less than 4.2 mg/dL. Symptoms of hypocalcemia usually occur when ionized levels fall to <2.5 mg/dL.
-Parathyroid hormone: decreased levels occur in hypoparathyroidism.
-Magnesium and phosphorus levels:  may be checked to indentify potential causes of hypocalcemia.

Treatment should be based on:
(1) Symptoms present: Paresthesias, tetany, carpopedal spasm, seizures
(2) Signs: Chvosek's or Trousseau's signs, impaired cardiac contractility, prolongation of the QT interval, bradycardia).
(3) Absolute level of calcium
(4) Rate of decrease (e.g. acute versus chronic decrease).

The therapeutic approach and management of hypocalcemia depends largely on the severity of symptoms and the underlying cause.  In patients with asymptomatic hypocalcemia, it is important to verify with repeat measurement (ionized or total calcium corrected for serum albumin).

Calcium Requirements

Calcium Supplementation Based on Age


The amount of calcium you need each day depends on your age. Average daily recommended amounts are listed below in milligrams (mg):

Birth to 6 months 200 mg
Infants 7–12 months 260 mg
Children 1–3 years 700 mg
Children 4-8 years 1,000 mg
Children 9–13 years 1,300 mg
Teens 14–18 years 1,300 mg
Adults 19–50 years 1,000 mg
Adult men 51–70 years 1,000 mg
Adult women 51–70 years 1,200 mg
Adults 71 years and older 1,200 mg
Pregnant and breastfeeding teens 1,300 mg
Pregnant and breastfeeding adults 1,000 mg

Upper limits - calcium:

The safe upper limits for calcium are listed below. Most people do not get amounts above the upper limits from food alone; excess intakes usually come from the use of calcium supplements. Surveys show that some older women in the United States probably get amounts somewhat above the upper limit since the use of calcium supplements is common among these women.

Birth to 6 months 1,000 mg
Infants 7-12 months 1,500 mg
Children 1-8 years 2,500 mg
Children 9-18 years 3,000 mg
Adults 19-50 years 2,500 mg
Adults 51 years and older 2,000 mg
Pregnant and breastfeeding teens 3,000 mg
Pregnant and breastfeeding adults 2,500 mg

Looking for additional info regarding electrolytes?

  Electrolyte Section  

Vitamin D:  Reference Intakes  /  RDA


Intake reference values for vitamin D and other nutrients are provided in the Dietary Reference Intakes (DRIs) developed by the Food and Nutrition Board (FNB) at the Institute of Medicine of The National Academies (formerly National Academy of Sciences). DRI is the general term for a set of reference values used to plan and assess nutrient intakes of healthy people. These values, which vary by age and gender, include:

  • Recommended Dietary Allowance (RDA): average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy people.
  • Adequate Intake (AI): established when evidence is insufficient to develop an RDA and is set at a level assumed to ensure nutritional adequacy.
  • Tolerable Upper Intake Level (UL): maximum daily intake unlikely to cause adverse health effects.

The FNB established an RDA for vitamin D representing a daily intake that is sufficient to maintain bone health and normal calcium metabolism in healthy people. RDAs for vitamin D are listed in both International Units (IUs) and micrograms (mcg); the biological activity of 40 IU is equal to 1 mcg (Table 2). Even though sunlight may be a major source of vitamin D for some, the vitamin D RDAs are set on the basis of minimal sun exposure.

Table 2: Recommended Dietary Allowances (RDAs) for Vitamin D
Age Male Female Pregnancy Lactation
0–12 months* 400 IU
(10 mcg)
400 IU
(10 mcg)
1–13 years 600 IU
(15 mcg)
600 IU
(15 mcg)
14–18 years 600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
19–50 years 600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
600 IU
(15 mcg)
51–70 years 600 IU
(15 mcg)
600 IU
(15 mcg)
>70 years 800 IU
(20 mcg)
800 IU
(20 mcg)



Health Risks from Excessive Vitamin D

Vitamin D toxicity can cause non-specific symptoms such as anorexia, weight loss, polyuria, and heart arrhythmias. More seriously, it can also raise blood levels of calcium which leads to vascular and tissue calcification, with subsequent damage to the heart, blood vessels, and kidneys [1]. The use of supplements of both calcium (1,000 mg/day) and vitamin D (400 IU) by postmenopausal women was associated with a 17% increase in the risk of kidney stones over 7 years in the Women's Health Initiative. A serum 25(OH)D concentration consistently >500 nmol/L (>200 ng/mL) is considered to be potentially toxic.

Excessive sun exposure does not result in vitamin D toxicity because the sustained heat on the skin is thought to photodegrade previtamin D3 and vitamin D3 as it is formed. In addition, thermal activation of previtamin D3 in the skin gives rise to various non-vitamin D forms that limit formation of vitamin D3 itself. Some vitamin D3 is also converted to nonactive forms [1]. Intakes of vitamin D from food that are high enough to cause toxicity are very unlikely. Toxicity is much more likely to occur from high intakes of dietary supplements containing vitamin D.

Long-term intakes above the UL increase the risk of adverse health effects [1] (Table 4). Most reports suggest a toxicity threshold for vitamin D of 10,000 to 40,000 IU/day and serum 25(OH)D levels of 500–600 nmol/L (200–240 ng/mL). While symptoms of toxicity are unlikely at daily intakes below 10,000 IU/day, the FNB pointed to emerging science from national survey data, observational studies, and clinical trials suggesting that even lower vitamin D intakes and serum 25(OH)D levels might have adverse health effects over time. The FNB concluded that serum 25(OH)D levels above approximately 125–150 nmol/L (50–60 ng/mL) should be avoided, as even lower serum levels (approximately 75–120 nmol/L or 30–48 ng/mL) are associated with increases in all-cause mortality, greater risk of cancer at some sites like the pancreas, greater risk of cardiovascular events, and more falls and fractures among the elderly. The FNB committee cited research which found that vitamin D intakes of 5,000 IU/day achieved serum 25(OH)D concentrations between 100–150 nmol/L (40–60 ng/mL), but no greater. Applying an uncertainty factor of 20% to this intake value gave a UL of 4,000 IU which the FNB applied to children aged 9 and older, with corresponding lower amounts for younger children.

Table 4: Tolerable Upper Intake Levels (ULs) for Vitamin D [1]
Age Male Female Pregnancy Lactation
0–6 months 1,000 IU
(25 mcg)
1,000 IU
(25 mcg)
7–12 months 1,500 IU
(38 mcg)
1,500 IU
(38 mcg)
1–3 years 2,500 IU
(63 mcg)
2,500 IU
(63 mcg)
4–8 years 3,000 IU
(75 mcg)
3,000 IU
(75 mcg)
greater than or equal9 years 4,000 IU
(100 mcg)
4,000 IU
(100 mcg)
4,000 IU
(100 mcg)
4,000 IU
(100 mcg)


1. Institute of Medicine, Food and Nutrition Board. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: National Academy Press, 2010.
Corrected Calcium for serum albumin conc