From the Research
The main difference between whole blood sodium and serum sodium is that whole blood sodium measurements are typically 1.9 mmol/L lower than serum sodium measurements, as shown in a study published in the European Journal of Endocrinology in 2019 1. This difference is due to the presence of blood cells in whole blood samples, which occupy volume but contain less sodium than plasma.
- Whole blood sodium is measured directly from whole blood samples and typically ranges from 135-145 mEq/L.
- Serum sodium is measured from the liquid portion of blood after clotting (serum) and normally ranges from 135-145 mEq/L.
- Serum sodium is the standard clinical measurement used to assess sodium status in patients. The values are generally similar, but the difference becomes clinically significant in conditions with abnormal cell volumes, such as severe anemia or polycythemia.
- When interpreting sodium levels, it's essential to know which measurement was used, especially in critical care settings where point-of-care testing might use whole blood analysis. Most clinical decisions and reference ranges in medical literature are based on serum sodium values, making it the preferred measurement in routine clinical practice.
- The study published in the European Journal of Endocrinology in 2019 1 analyzed 878 sodium measurements and found a significant difference between indirect and direct ion-selective electrode (ISE) methods, highlighting the importance of using the same method in critical situations to avoid false decisions due to measurement differences.