Laboratory Units for Sodium and Chloride
Sodium and chloride levels in laboratory tests are typically reported in millimoles per liter (mmol/L) or milliequivalents per liter (mEq/L), which are numerically equivalent for these monovalent ions. 1, 2
Standard Reporting Units
- Sodium (Na+): Reported as mmol/L or mEq/L in serum or plasma 1, 2, 3
- Chloride (Cl-): Reported as mmol/L or mEq/L in serum or plasma 1, 2, 3
These units are interchangeable for sodium and chloride because both are monovalent ions (single charge), making 1 mmol = 1 mEq for these electrolytes. 1
Clinical Context and Normal Ranges
- Normal serum sodium: Approximately 136-145 mmol/L 1
- Normal serum chloride: Approximately 98-107 mmol/L 1
The sodium-chloride difference (Na+ - Cl-) is also clinically relevant and typically ranges from 36-43 mmol/L in healthy individuals. 3
Measurement Methods
Multiple analytical methods are used for electrolyte determination: 2
- Sodium and potassium: Flame atomic emission spectrometry, ion-selective electrodes after sample dilution, or enzymatic methods 2
- Chloride: Coulometry, absorption spectrometry after chemical reaction, or enzymatic methods 2
Important Technical Considerations
Ion-selective electrodes without sample dilution measure ionized electrolyte concentration in serum water [S(W)], reported as mmol/kg, which provides more accurate physiologic information independent of the sample's water content. 2
- Total electrolyte concentration in serum requires knowledge of the water concentration or lipid/protein concentration for accurate medical interpretation 2
- Ionized measurements avoid interference from the electrolyte-free compartment (lipids and proteins) 2
Extreme Values Compatible with Survival
Documented survivable extreme values (with patients living ≥28 days) include: 4
These extreme values deviated 7 standard deviations or more from population means, demonstrating the wide range of values patients can survive with appropriate management. 4