Albumin is a common protein produced by the liver, circulating abundantly in the bloodstream. Calcium is a mineral that plays a role in numerous bodily functions, including bone health, nerve transmission, and muscle contraction. A significant portion of the calcium in your blood is linked to albumin. Changes in albumin levels can influence how calcium is measured in routine blood tests.
Albumin’s Role in Calcium Levels
Albumin is the primary carrier protein for calcium in the bloodstream, binding roughly 40% to 50% of the total calcium. This binding occurs at specific negatively charged sites on the albumin molecule, which attract the positively charged calcium ions. This creates a reservoir of calcium that can be released when needed by the body. When albumin levels are lower than typical, there are fewer binding sites available for calcium. Fewer binding sites mean less calcium will be bound to protein, directly influencing the total calcium measured in a blood test.
Differentiating Calcium Measurements
When calcium levels are assessed, two primary measurements are used: “total calcium” and “ionized calcium.” Total calcium measures all calcium in the blood, including protein-bound and free calcium. Ionized calcium measures only the free, unbound form. This is the active form the body uses for functions like nerve conduction and muscle contraction.
Low albumin primarily affects the protein-bound portion of total calcium. If albumin is low, total calcium may appear low, even if active ionized calcium levels are normal. For example, a 1 g/dL decrease in serum albumin below 4 g/dL can cause total calcium to decrease by approximately 0.8 mg/dL. This distinction is important; a low total calcium reading due to low albumin may not indicate a true calcium deficiency.
Why “Corrected” Calcium is Important
Due to albumin’s influence on total calcium measurements, healthcare professionals often use a calculation called “corrected calcium” or “albumin-adjusted calcium.” This calculation aims to estimate the true calcium status when albumin levels are abnormal. The common formula for corrected calcium involves adding 0.8 mg/dL to the measured total calcium for every 1 g/dL decrease in albumin below 4 g/dL.
This adjustment helps prevent misdiagnosis of calcium imbalances. Without this correction, a patient with low albumin might be incorrectly identified as having low calcium, potentially leading to unnecessary medical interventions. While the corrected calcium formula can be helpful, direct measurement of ionized calcium is considered a more accurate assessment of calcium status, particularly in complex cases or critical care settings.