Corrected Sodium Calculator
Estimates true serum sodium by correcting for the dilutional effect of hyperglycaemia. Critical in diabetic ketoacidosis (DKA), hyperosmolar hyperglycaemic state (HHS), and any clinical scenario where severe hyperglycaemia may mask the underlying sodium status.
Calculate Corrected Sodium
Enter the patient’s measured serum sodium and blood glucose. This calculator provides both the classic Katz (1.6 mEq/L) correction and the Hillier (2.4 mEq/L) correction, which may be more accurate at glucose levels above 400 mg/dL.
The corrected sodium reveals the underlying sodium status that will become apparent once glucose normalises. This is especially critical in DKA and HHS — a corrected sodium that is already high or rising suggests significant free water deficit and a risk of hypernatraemia as insulin is administered.
Understanding Corrected Sodium
Glucose is an osmotically active solute. When blood glucose rises significantly (typically above 100 mg/dL), the osmotic gradient created draws water from the intracellular space into the extracellular compartment. This dilutes the extracellular sodium, causing a dilutional or “translocational” hyponatraemia. The measured sodium appears artificially low — the total body sodium has not changed, but its concentration has been diluted by the water shift.
Correcting sodium for hyperglycaemia estimates what the sodium concentration would be if glucose were normal. This is essential for two reasons: first, to determine whether a true sodium disorder exists alongside the glucose problem; and second, to predict what will happen to sodium as glucose is corrected with insulin therapy.
Katz Formula (1973)
Corrected Na⁺ = Measured Na⁺ + 1.6 × ((Glucose − 100) / 100)
The classic correction factor. Adds 1.6 mEq/L to measured sodium for each 100 mg/dL rise in glucose above 100. Most widely used and recommended by most guidelines.
Hillier Formula (1999)
Corrected Na⁺ = Measured Na⁺ + 2.4 × ((Glucose − 100) / 100)
Proposed as more accurate at glucose levels >400 mg/dL. Adds 2.4 mEq/L per 100 mg/dL glucose rise. May better predict the sodium trajectory in severe hyperglycaemia.
Key distinction: The Katz correction (1.6) is the standard used by most guidelines and textbooks. The Hillier correction (2.4) was derived from hypertonic saline infusion studies and may be more accurate at very high glucose levels (>400 mg/dL). In practice, the true correction factor likely falls between 1.6 and 2.4 and varies between patients. Both values are provided for clinical reference.
Interpreting Corrected Sodium
Once the corrected sodium is calculated, interpret it using the standard sodium reference range. The corrected value predicts the sodium the patient will have once glucose normalises — this is the clinically actionable number for fluid management decisions.
| Corrected Na⁺ (mEq/L) | Category | Clinical Significance in Hyperglycaemia |
|---|---|---|
| < 120 | Severe hyponatraemia | True concurrent hyponatraemia alongside hyperglycaemia. Risk of cerebral oedema. Careful correction rate essential — avoid exceeding 8–10 mEq/L in 24 hours. |
| 120 – 129 | Moderate hyponatraemia | Genuine sodium deficit exists. In DKA/HHS, fluid resuscitation with 0.9% NaCl is appropriate. Monitor sodium closely during insulin therapy. |
| 130 – 135 | Mild hyponatraemia | Mild sodium deficit or dilutional. In DKA, 0.9% NaCl is usually continued. Re-check corrected sodium with each glucose measurement. |
| 136 – 145 | Normal | The apparent measured hyponatraemia is entirely explained by the glucose-driven water shift. No true sodium disorder. Continue standard DKA/HHS protocol. |
| 146 – 155 | Hypernatraemia | Significant free water deficit exists alongside hyperglycaemia. Consider switching to 0.45% NaCl once haemodynamically stable. High risk of rising sodium as glucose corrects — monitor closely. |
| > 155 | Severe hypernatraemia | Profound dehydration with massive free water deficit. Commonly seen in HHS. Cautious free water replacement essential. Avoid correcting sodium by more than 10–12 mEq/L per 24 hours to prevent cerebral oedema. |
Trending matters more than a single value. In DKA/HHS, the corrected sodium should rise as glucose falls with insulin therapy. A falling corrected sodium during treatment is a red flag — it suggests excessive free water administration or inadequate sodium replacement, and is associated with increased risk of cerebral oedema, particularly in children and young adults.
Clinical Context & Differential Diagnosis
Corrected sodium is most critical in the emergency management of diabetic crises. Understanding the underlying sodium status guides fluid selection and predicts the trajectory of sodium as glucose is treated.
Corrected Sodium in Diabetic Emergencies
In DKA, the measured sodium is typically low (120–130 mEq/L) due to the osmotic water shift from hyperglycaemia. The corrected sodium reveals the true sodium status — in many cases, the corrected value is normal or even elevated, reflecting the significant water and sodium losses from osmotic diuresis, vomiting, and poor oral intake. The corrected sodium is a key parameter in DKA management protocols.
During treatment with insulin and IV fluids, glucose falls and water shifts back intracellularly. The measured sodium should rise by approximately 1.6 mEq/L for every 100 mg/dL drop in glucose. If the measured sodium does not rise — or falls — this indicates excessive free water relative to sodium and warrants a change in fluid strategy (switch from 0.45% to 0.9% NaCl, or reduce free water rate).
HHS typically presents with more extreme hyperglycaemia (glucose often >600 mg/dL, sometimes >1000 mg/dL) and more profound dehydration than DKA. The corrected sodium in HHS is often significantly elevated (150+ mEq/L), reflecting massive free water losses from sustained osmotic diuresis. Total body water deficits in HHS may exceed 10–12 litres.
Fluid management in HHS requires particular care: initial resuscitation with 0.9% NaCl for volume restoration, then consideration of 0.45% NaCl once haemodynamically stable if the corrected sodium is elevated. Glucose and osmolality should be reduced slowly — no faster than 3 mOsm/kg/hr — to avoid cerebral oedema. Insulin is used cautiously and at lower doses than in DKA because the primary pathology is dehydration, not ketoacidosis.
The corrected sodium directly guides the choice of IV fluid in hyperglycaemic emergencies. If the corrected sodium is low or normal (<145 mEq/L), 0.9% NaCl is generally appropriate — it replaces both the sodium and volume deficit. If the corrected sodium is elevated (>145 mEq/L), a switch to 0.45% NaCl (half-normal saline) should be considered once the patient is haemodynamically stable to provide more free water and prevent further sodium rise.
Many DKA/HHS protocols recommend rechecking electrolytes (including sodium and glucose) every 1–2 hours during the initial phase of treatment. The corrected sodium should be recalculated each time to track the trajectory and adjust fluids accordingly.
Other Causes of Hyponatraemia to Exclude
Pseudohyponatraemia occurs when the measured sodium is falsely low due to laboratory artefact — typically from severe hyperlipidaemia or hyperproteinaemia displacing the aqueous phase in which sodium is measured. This is an issue with indirect ion-selective electrode (ISE) methods used in many central laboratories. Direct ISE methods (point-of-care blood gas analysers) are not affected. Pseudohyponatraemia is isotonic — serum osmolality is normal. Corrected sodium for hyperglycaemia does not apply here because the problem is measurement methodology, not osmotic water shifts.
If the corrected sodium is still low after accounting for glucose, the patient has a genuine concurrent sodium problem. This may be caused by excessive free water intake (polydipsia in uncontrolled diabetes), SIADH (especially if the patient is on medications that cause it, such as SSRIs), adrenal insufficiency (which can coexist with type 1 diabetes in autoimmune polyglandular syndrome), or significant sodium losses from vomiting, diarrhoea, or diuretics. In these cases, the hyponatraemia should be evaluated and managed independently from the hyperglycaemia.
Mannitol, sorbitol, glycine (post-TURP syndrome), and radiocontrast agents can also cause a translocational hyponatraemia through the same osmotic water-shift mechanism as glucose. The sodium correction formula for glucose does not apply to these substances. If these solutes are suspected, serum osmolality and the osmolar gap should be calculated directly. Ethanol and toxic alcohols (methanol, ethylene glycol) increase serum osmolality but do not typically cause translocational hyponatraemia because they distribute freely across cell membranes.
Step 1: Correct sodium for glucose using the Katz formula. Step 2: Assess the corrected sodium — is the patient truly hyponatraemic, normonatraemic, or hypernatraemic once glucose is accounted for? Step 3: Select IV fluids accordingly (0.9% NaCl if corrected Na⁺ ≤ 145; consider 0.45% NaCl if corrected Na⁺ > 145). Step 4: Recheck and recalculate every 1–2 hours during active treatment.
Common Pitfalls & Limitations
One of the most consequential errors in managing diabetic emergencies is failing to calculate the corrected sodium. A measured sodium of 125 mEq/L in a patient with glucose of 800 mg/dL may look like hyponatraemia, but the corrected sodium may be 136 mEq/L (Katz) or even 142 mEq/L (Hillier) — indicating no true sodium deficit. Failing to recognise this can lead to inappropriate selection of hypotonic fluids when isotonic saline is needed, or conversely, failure to recognise a dangerously high corrected sodium that warrants free water replacement.
A single corrected sodium value is informative, but the trend is what guides therapy. As insulin drives glucose into cells, water follows and the measured sodium should rise proportionally. The corrected sodium should remain stable or rise slowly. A falling corrected sodium during DKA treatment is a danger signal — it suggests excessive hypotonic fluid administration and is associated with cerebral oedema, particularly in paediatric patients. The corrected sodium should be recalculated with every set of electrolytes during active management.
The sodium correction formula only applies when glucose is elevated above the normal level (typically >100 mg/dL or >5.6 mmol/L). When glucose is normal, the measured sodium is the true sodium and no correction is needed. Applying the formula to euglycaemic patients would produce a spurious result. Additionally, the formula should not be applied to patients with hypoglycaemia — the correction was not designed or validated for glucose values below the normal range.
The debate between 1.6 and 2.4 mEq/L correction factors is ongoing. The Katz factor (1.6) was originally derived from theoretical osmotic considerations and is the standard in most textbooks and guidelines. The Hillier factor (2.4) was derived from experimental hypertonic saline infusion data and may more accurately predict sodium changes at very high glucose levels (>400 mg/dL). In practice, the true correction probably lies somewhere between the two and varies with the rate of glucose rise. The key clinical message is that both are estimates — the measured sodium after glucose correction is what ultimately matters.
Translocational hyponatraemia (from hyperglycaemia) is fundamentally different from true hypotonic hyponatraemia (SIADH, diuretics, adrenal insufficiency). Translocational hyponatraemia is hypertonic — the serum osmolality is elevated, not reduced. It resolves spontaneously as glucose normalises. True hyponatraemia in the setting of hyperglycaemia exists when the corrected sodium is still low — this requires its own workup and management, independent of the glucose problem. Mixing up the two can lead to dangerous overcorrection of sodium or inappropriate fluid restriction.
Quick Reference Summary
| Clinical Scenario | Action |
|---|---|
| DKA with measured Na⁺ 125, glucose 700 | Correct Na⁺ → likely ~135 (Katz) or ~139 (Hillier). Measured hyponatraemia is translocational. Use 0.9% NaCl. |
| Corrected Na⁺ > 145 in DKA/HHS | Significant free water deficit. Once haemodynamically stable, consider 0.45% NaCl. Monitor for rising sodium as glucose corrects. |
| Corrected Na⁺ falling during DKA treatment | Red flag — excessive free water. Risk of cerebral oedema. Increase sodium content of fluids (switch to or continue 0.9% NaCl). |
| Corrected Na⁺ still low after glucose correction | True concurrent hyponatraemia — investigate independently (check osmolality, urine electrolytes, cortisol, thyroid). |
The Golden Rule: Always calculate corrected sodium in any patient with hyperglycaemia before interpreting their sodium status. The corrected sodium predicts where the patient’s sodium is heading — it is the value that guides your fluid strategy.
Disclaimer & References
For Educational Purposes Only. This calculator and the accompanying clinical information are intended as educational tools for healthcare professionals. They do not replace clinical judgement. Results should be interpreted in the full clinical context. Lab reference ranges vary by institution — verify with your own laboratory. Drug dosages should be confirmed against current prescribing information.
References
- Katz MA. Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression. The New England Journal of Medicine. 1973;289(16):843–844. DOI: 10.1056/NEJM197310182891607
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. The American Journal of Medicine. 1999;106(4):399–403. DOI: 10.1016/S0002-9343(99)00055-8
- Kitabchi AE, Umpierrez GE, Miles JM, Fisher JN. Hyperglycemic crises in adult patients with diabetes. Diabetes Care. 2009;32(7):1335–1343. DOI: 10.2337/dc09-9032
- Umpierrez GE, Khajavi M, Kitabchi AE. Review: diabetic ketoacidosis and hyperglycemic hyperosmolar nonketotic syndrome. The American Journal of the Medical Sciences. 1996;311(5):225–233. DOI: 10.1097/00000441-199605000-00006
- Wolfsdorf JI, Glaser N, Agus M, et al. ISPAD Clinical Practice Consensus Guidelines 2018: diabetic ketoacidosis and the hyperglycemic hyperosmolar state. Pediatric Diabetes. 2018;19(Suppl 27):155–177. DOI: 10.1111/pedi.12701
- Hoorn EJ, Carlotti AP, Costa LA, et al. Preventing a drop in effective plasma osmolality to minimize the likelihood of cerebral edema during treatment of children with diabetic ketoacidosis. The Journal of Pediatrics. 2007;150(5):467–473. DOI: 10.1016/j.jpeds.2006.11.062
- Spasovski G, Vanholder R, Allolio B, et al. Clinical practice guideline on diagnosis and treatment of hyponatraemia. European Journal of Endocrinology. 2014;170(3):G1–G47. DOI: 10.1530/EJE-13-1020
- Verbalis JG, Goldsmith SR, Greenberg A, et al. Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. The American Journal of Medicine. 2013;126(10 Suppl 1):S1–S42. DOI: 10.1016/j.amjmed.2013.07.006