Calcium, Ionized, Serum

Optimal Result: 4.5 - 5.6 mg/dL, or 1.12 - 1.40 mmol/L.

Calcium is an important mineral found throughout the body. Not only is it important for bone health, but it is important cell communication, blood clotting, muscle contraction, and nerve cell function. The amount of calcium in the body and blood is regulated by several substances including parathyroid hormone, calcitonin, estrogen, and vitamin D, among others. Almost all calcium in the body is found within the bones and teeth. Compared to this, the amount of calcium found outside in the serum is small. However, the amount of calcium found in the serum is an important biomarker. About half of calcium in the blood is bound to proteins and other molecules. However, the other half of blood calcium floats freely in the serum. This free calcium or ionized serum calcium is biologically active and measured directly by the ionized serum calcium test. Serum calcium is usually reported in units of mg/dL in the United States and in mmol/L in many other countries. It may also be reported as mEq/L.

Normal Ranges for ionized calcium:

Men: 4.64 to 5.28 mg/dL

Women: 4.64 to 5.28 mg/dL

Children to up 18 years of age: 4.8 to 5.52 mg/dL

Critical Range: More than 7 mg/dL or less than 2 mg/dL



What does it mean if your Calcium, Ionized, Serum result is too high?

High calcium levels can make people thirsty and urinate more frequently, It can also cause kidney stones and other kidney problems. People may have muscle weakness and bone pain. Those with high serum calcium may find it difficult to think or concentrate, they may become confused or irritable. People may experience nausea, vomiting, and constipation. Low calcium affects the heart, too, causing a slow heart rate by high blood pressure. Calcium intake alone is rarely the cause of elevated serum calcium. The amount of albumin in the blood can affect the ionized serum calcium measurement. If there is too much albumin in the blood, free calcium may seem like it is too high when it may be normal.

Some specific causes of high ionized calcium are:

- Hypoalbuminemia

- Hyperparathyroidism

- Metabolic acidosis

- Sarcoidosis

- Cancer

What does it mean if your Calcium, Ionized, Serum result is too low?

Low levels of calcium can cause a number of signs and symptoms. People generally have problems with nerves and muscles first. People with low serum calcium may experience pins and needles feeling around the mouth, muscle twitches and spasms, and even seizures. Low calcium can affect the beating of the heart, too, causing rhythm problems and low blood pressure. Chronically low levels of calcium dry skin, dental diseases, and dementia. The amount of albumin in the blood can affect the ionized serum calcium measurement. If there is too little albumin in the blood, free calcium may appear as if it is too low when it may be normal.

Some specific causes of low ionized calcium are:

- Acute respiratory alkalosis

- Chronic respiratory alkalosis

- Hyperventilation

- Bicarbonate infusion

- Critical illness

- Toxic shock syndrome

- Hypoparathyroidism 

- Vitamin D deficiency

- Magnesium deficiency

- Hyperphosphatemia 


To increase ionized calcium levels in serum, it is essential to incorporate calcium-rich foods and possibly Vitamin D, either through diet or supplements, as Vitamin D aids in calcium absorption. Calcium supplements might be necessary but should be taken under medical supervision to avoid excessive intake.

Addressing any underlying medical conditions that might be contributing to low calcium levels, such as hypoparathyroidism or kidney disease, is also important.

In individuals with chronic kidney disease (CKD), serum calcium levels can become low due to the kidneys' diminished ability to convert vitamin D to its active form, which is essential for calcium absorption. Normally, our bodies acquire vitamin D through food and sunlight exposure, and healthy kidneys transform this vitamin D into an active form that aids in calcium absorption. However, in CKD, the reduced capacity to activate vitamin D leads to decreased calcium absorption from food, consequently lowering blood calcium levels. Additionally, elevated phosphorus levels, common in CKD, can bind with calcium in the blood, further reducing serum calcium levels. Research involving thousands of CKD patients has established a correlation between low serum calcium levels and an accelerated progression to kidney failure, as well as an association with low vitamin D levels indicative of worsening kidney function. To maintain normal serum calcium levels, a well-balanced diet rich in nutrients like magnesium and vitamin D, which aid in calcium absorption, is essential. Consulting a dietitian specializing in kidney health can help tailor a diet to individual needs, considering that dairy foods, while high in calcium, often contain phosphorus, which is typically restricted in CKD diets. The healthcare team might suggest vitamin D supplements or phosphate binders containing calcium, but these should only be taken if prescribed. Medications affecting calcium levels may require adjustment, and regular blood tests are crucial for monitoring ionized calcium levels, ensuring they stay within a healthy range, and for adjusting treatment strategies. Professional medical advice is vital before making any significant dietary or medication changes.

Frequently asked questions

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