What is the Difference Between Calcium and Corrected Calcium

Calcium is an essential mineral that plays a vital role in numerous physiological functions in the human body. In clinical practice, it is important to measure and interpret calcium levels accurately to diagnose and manage various health conditions.

What is the difference between calcium and corrected calcium? In clinical investigations, total calcium levels represent both ionized and protein-bound calcium, with about 15% bound to organic and inorganic anions, about 40% bound to albumin, and the remainder as active ionized calcium. Corrected calcium levels are calculated to account for variations in albumin levels, which gives a more accurate reflection of biologically active calcium.

Key Areas Covered

1. What is Calcium  
      – Definition, Function
2. What is Corrected Calcium
      – Definition, Function
3. Similarities Between Calcium and Corrected Calcium
      – Outline of Common Features
4. Difference Between Calcium and Corrected Calcium
      – Comparison of Key Differences
5. FAQ: Calcium and Corrected Calcium
      – Answers to Frequently Asked Questions

Key Terms

Calcium, Corrected Calcium, Test

What is Calcium

Calcium is a mineral necessary for various bodily functions. The normal blood calcium level for adults typically ranges from 8.5 to 10.2 milligrams per deciliter (2.25 – 2.60 mmol/L), though these reference ranges can vary between laboratories.

Calcium is mainly obtained through dietary intake, with common sources including dairy products, leafy greens, and fortified foods. In the body, over 99% of calcium is stored in bones, where it plays a crucial role in bone mineralization. The remaining calcium, less than 1%, is in plasma and exists either in a free ionized form or bound to proteins such as albumin. Ionized calcium is the biologically active form that is essential for several physiological processes, including intra- and extracellular signaling as ionized calcium plays a critical role in cellular communication and, signal transduction, nerve impulse transmission as it is vital for the proper functioning of the nervous system, muscle contraction as calcium is necessary for muscle contraction, including the heart muscle.

Various factors can influence calcium levels in the blood, such as pH changes, different disease conditions, and organ functions. pH changes influence calcium levels. An increase in pH (alkalosis) can decrease free ionized calcium levels. Symptoms of hypocalcemia or hypercalcemia can develop with pH changes, even if total serum calcium remains unchanged. Altered kidney function can change the calcium levels as the kidneys filter ionized calcium, and any dysfunction can impact calcium balance. Multiple diseases and conditions such as hyperparathyroidism, certain cancers (lung, breast, and blood cancers), kidney failure, and vitamin D deficiency can alter calcium levels. Diseases that cause malabsorption, like celiac disease, can also affect calcium absorption and levels.

What is Corrected Calcium

Serum calcium levels are routinely measured using total calcium measurements corrected for albumin. This correction is necessary because changes in plasma albumin concentration can affect total calcium concentration independently of the ionized calcium concentration, potentially leading to misinterpretation of results.

In hypoalbuminemia or hypoalbuminemia states, total serum calcium may not accurately reflect the biologically active ionized calcium. For instance, a low albumin level can lead to an underestimation of the active calcium when measuring only total calcium. Therefore, corrected calcium is calculated to provide a more accurate estimation of the active form of calcium in the blood.

Several formulas are used to adjust calcium levels based on albumin concentration. The Payne formula is the most commonly used in practice. The corrected calcium can be calculated using the following formula:

Corrected Calcium (mg/dL)= (0.8 * (Normal Albumin – Patient’s Albumin)) + Serum Calcium
Corrected Calcium (mmol/L) = (0.02 * (Normal Albumin – Patient’s Albumin)) + Serum Calcium

Similarities Between Calcium and Corrected Calcium

1. Both are measurements help to assess calcium levels in the blood.
2. Both total calcium and corrected calcium measurements include ionized calcium.
3. They help to diagnose various health conditions in the body.

Difference Between Calcium and Corrected Calcium

Definition

• Total calcium levels consist of about 15% bound to organic and inorganic anions, about 40% bound to albumin, and the remaining as biologically active ionized calcium, while corrected calcium is the adjusted calcium levels to account for variations in albumin levels, providing a more accurate reflection of the biologically active calcium.

Measure

• While total calcium provides an overview of calcium levels, corrected calcium offers a more precise measure by accounting for albumin variations.

FAQ: Calcium and Corrected Calcium

1. What is the normal calcium level?

Normal blood calcium level for adults typically ranges from 8.5 to 10.2 milligrams per deciliter (2.25 – 2.60 mmol/L. However, it’s important to note that these reference ranges can vary between laboratories.

2. Why is a corrected calcium level used?

This correction is used because changes in plasma albumin concentration can affect total calcium concentration independently of the ionized calcium concentration, potentially leading to misinterpretation of results. For example, in hypoalbuminemic or hyperalbuminemic states.

3. What is the difference between calcium and ionized calcium?

Calcium refers to the total amount of calcium in the blood, including both bound and free forms, while ionized calcium specifically measures the free, biologically active form of calcium not bound to proteins.

4. Which calcium test is best?

For general health, we can usually use a blood calcium test. It is easier to measure and less expensive. For bone health, a bone density test (DEXA scan) is more appropriate.

Reference:

1. “Calcium Blood Test.” Cleveland Clinic.
2. “Calcium Correction for Hypoalbuminemia.” Reference Medscape.

Image Courtesy:

1. “Calcium balance” By Cruithne9 – Own work (CC BY-SA 4.0) via Commons Wikimedia