From the Guidelines
The normal range for ionized calcium is 1.1–1.3 mmol/L, as stated in the most recent guideline 1. This range is crucial for maintaining various physiological processes, including muscle contraction, nerve conduction, blood clotting, and hormone secretion. Ionized calcium levels are tightly regulated by parathyroid hormone (PTH), vitamin D, and calcitonin to maintain homeostasis. Some key points to consider when measuring ionized calcium include:
- The measurement should be collected anaerobically to prevent falsely lowered values due to pH changes 1.
- Ionized calcium is essential for the formation and stabilization of fibrin polymerization sites and many platelet-related functions 1.
- Hypocalcemia, or low ionized calcium levels, can negatively impact cardiac contractility and systemic vascular resistance, and is associated with increased mortality and the need for multiple transfusions 1.
- The preferred agent to correct hypocalcemia is calcium chloride, which contains 270 mg of elemental calcium per 10 mL of a 10% solution, making it a more effective option than calcium gluconate 1. In critical care settings, monitoring and maintaining ionized calcium levels within the normal range is vital, especially during massive transfusion, as hypocalcemia can have severe consequences 1.
From the Research
Normal Range for Ionized Calcium
The normal range for ionized calcium can vary depending on the source and methodology used.
- According to a study published in 2008 2, the normal range for ionized calcium was achieved in a patient after treatment, with levels stabilizing within 24 hours.
- A study from 2014 3 found that the relationship between ionized calcium levels and clinical outcome follows a "U" shaped curve, with the nadir at the normal range, extending slightly to hypercalcemia. The normal range for ionized calcium was not explicitly stated, but the study found that moderate hypocalcemia was associated with increased risk of death.
- A 2017 review 4 stated that a normal serum calcium level is 8 to 10 mg/dL, but did not provide a specific range for ionized calcium.
- A study published in 2021 5 defined hypocalcemia and hypercalcemia by the lowest and highest 2.5 percentiles, respectively, using the central 95% reference interval, but did not provide a specific normal range for ionized calcium.
- An older study from 1978 6 found that the normal range for ionized calcium in serum from normal cows implies that the ionized calcium fraction comprises 43.4 ± 3.0 % of the total serum calcium, but this may not be directly applicable to humans.
Ionized Calcium Levels and Health Outcomes
- The study from 2014 3 found that mild hypercalcemia in ionized calcium levels on ICU admission was protective, whereas moderate and mild hypocalcemia was associated with increased risk of death.
- The 2021 study 5 found that high plasma ionized calcium is associated with higher risk of myocardial infarction and ischemic stroke compared to plasma ionized calcium within the reference interval.
- The 2008 study 2 reported a case where citrate anticoagulation was used to correct ionized hypercalcemia, and the patient's ionized calcium levels decreased into the normal range within 8 hours.