Sodium Change in Hypertriglyceridemia Calculator

Understanding Pseudohyponatremia in Hypertriglyceridemia

When laboratory tests report low serum sodium (below 135 mEq/L), the reflex assumption is often true hyponatremia requiring intervention. However, severe hypertriglyceridemia—typically above 500 mg/dL—creates a measurement artefact known as pseudohyponatremia. The sodium concentration is calculated as: sodium content divided by total plasma volume. Triglycerides and proteins occupy plasma space, reducing the proportion available to water. This lipid displacement artificially lowers the sodium reading without affecting actual sodium atoms present.

The plasma volume consists of three components: water, proteins, and lipids. Sodium dissolves only in the aqueous portion. When lipids expand disproportionately, the denominator in the concentration equation grows, driving the reported value downward despite unchanged true sodium concentration. Standard automated analysers measuring sodium assume a fixed lipid-to-water ratio; severe hypertriglyceridemia violates this assumption, producing false hyponatremia.

Correcting Sodium for Triglyceride Effect

The sodium correction accounts for triglyceride-induced plasma volume expansion. Each mg/dL of triglycerides above the normal range displaces a small but measurable fraction of plasma water. Use the following formulas to derive the corrected serum sodium:

• Measured sodium — Serum sodium concentration from laboratory report (mEq/L); normal range 135–145 mEq/L
• Triglycerides — Serum triglyceride level (mg/dL or mmol/L); values above 150 mg/dL may cause pseudohyponatremia
• Sodium change — Magnitude of sodium depression attributable to triglyceride-induced volume displacement (mEq/L)
• Corrected sodium — True serum sodium concentration after accounting for triglyceride interference (mEq/L)

Clinical Conditions Behind Pseudohyponatremia

Hypertriglyceridemia is the most common culprit, but other conditions featuring elevated protein or lipid concentrations produce the same effect:

• Severe hypertriglyceridemia – from genetic lipid disorders, uncontrolled diabetes, or medication side-effects
• Multiple myeloma – immunoglobulin M paraproteins expand plasma volume significantly
• Waldenström macroglobulinemia – similar mechanism to myeloma, though rarer
• Intravenous immunoglobulin (IVIG) infusion – large protein loads temporarily increase plasma protein concentration
• Hypercholesterolaemia – exceptionally rare as a sole cause, but can contribute alongside hypertriglyceridemia

Distinguishing pseudohyponatremia from genuine hyponatraemia using this calculator is essential. Treating pseudohyponatraemia with sodium supplementation can precipitate hypernatraemia and serious neurological harm.

Critical Pitfalls and Clinical Considerations

Several common mistakes in interpretation and application of the sodium correction can lead to patient harm.

1. Sodium supplementation in pseudohyponatraemia is dangerous — The corrected sodium is normal; administering sodium-containing fluids or salt tablets worsens hypernatraemia risk. The error is recognising pseudohyponatraemia, not treating it with sodium. The underlying hypertriglyceridemia requires management (statins, lifestyle change, fibrates), not sodium replacement.
2. Triglyceride measurement method matters — Some laboratories use enzymatic methods that perform poorly above 500 mg/dL; others require dilution or alternative assays. Always verify the laboratory's triglyceride value is reliable at extreme concentrations. Rechecking borderline cases with a reference lab prevents cascade misdiagnosis.
3. Correct for triglycerides alone, not proteins — Although hyperproteinaemia also causes pseudohyponatraemia (roughly 2.5 mEq/L per 10 g/dL of protein), this calculator addresses triglyceride displacement only. If both hypertriglyceridemia and hyperproteinaemia coexist, the effects are additive and a more comprehensive correction formula becomes necessary.
4. Symptoms guide the clinical picture — A truly asymptomatic patient with 'hyponatraemia' and elevated triglycerides is almost certainly experiencing pseudohyponatraemia. Conversely, a patient with genuine hyponatraemia symptoms (seizures, confusion) despite correction likely has a separate electrolyte problem or pseudohyponatraemia is incomplete. Symptoms trump numbers.

How to Use This Calculator

Begin by entering two laboratory values:

1. Measured serum sodium – transcribe directly from your lab report (units: mEq/L)
2. Serum triglycerides – enter the concentration in either mg/dL or mmol/L; the calculator converts automatically

The tool then computes the sodium shift caused by triglyceride displacement and displays the corrected sodium concentration. If the corrected value falls within the normal range (135–145 mEq/L) and the measured sodium was low, pseudohyponatraemia is present. A corrected sodium that remains below 135 mEq/L suggests genuine hyponatraemia alongside the triglyceride artefact, requiring additional investigation into osmolality, urine sodium, and fluid status.

Always interpret results within the full clinical context: patient symptoms, fluid intake and output, renal function, and medication history determine whether sodium intervention is truly warranted.