Sodium Correction Calculator for Glucose and Hyponatraemia

Sodium correction calculator: glucose and hyponatraemia

For healthcare professionals and students. Check results against your local protocols and clinical judgement; this tool does not give medical advice.

This sodium correction calculator covers the two calculations people usually mean by “sodium correction”. The first is the glucose-corrected sodium in hyperglycaemia: high glucose draws water out of cells and dilutes the sodium, so the measured value is adjusted by the Katz factor (1.6 mmol/L per 100 mg/dL of glucose above 100) or the Hillier factor (2.4). Both are shown side by side, with glucose in mg/dL or mmol/L.

The second is for hyponatraemia: the Adrogué–Madias estimate of how much one litre of a chosen fluid would change the serum sodium, and the rise so far between two results with the rate per hour, compared with a limit you set. For hypernatraemia and water deficits, use the free water deficit calculator, which offers the same glucose correction. Everything runs in your browser.

How to use the Sodium Correction Calculator

1. Under Calculation, choose Glucose (corrected sodium) or Hyponatraemia (change per litre and rate).
2. For glucose correction, enter the measured sodium and blood glucose (mg/dL or mmol/L) and pick the factor to headline.
3. For hyponatraemia, enter the serum sodium, weight, body water fraction and the fluid, including any potassium in it.
4. Under Rise so far, enter the starting and current sodium, the hours between them (up to 24) and your protocol’s limit.
5. Read the result, the working and the notes, and copy the summary if needed.

Sodium Correction Calculator features

Glucose-corrected sodium: Katz and Hillier

Corrected Na = measured Na + factor × (glucose mg/dL − 100) ÷ 100. Katz MA, N Engl J Med 1973;289(16):843–844, derived a fall of 1.6 mmol/L for every 100 mg/dL rise in glucose from the movement of water between body compartments. Hillier TA, Abbott RD and Barrett EJ, Am J Med 1999;106(4):399–403, raised glucose above 600 mg/dL in six healthy volunteers and measured an average fall of 2.4 mmol/L per 100 mg/dL. They found the relation was not linear: up to 400 mg/dL the 1.6 factor worked well, while above 400 mg/dL a factor of 4.0 was better, and they judged 2.4 the better overall estimate.

Worked example (self-test): sodium 130 mmol/L with glucose 600 mg/dL (33.3 mmol/L) gives 130 + 1.6 × 5 = 138 by Katz and 130 + 2.4 × 5 = 142 by Hillier. Corrected sodium is useful in diabetic ketoacidosis and hyperosmolar states; the effective osmolality is on the osmolality calculator.

Hyponatraemia: Adrogué–Madias and the rate of rise

Change in serum Na after 1 L = (fluid Na + fluid K − serum Na) ÷ (total body water + 1). Adrogué HJ and Madias NE, “Hyponatremia”, N Engl J Med 2000;342(21):1581–1589. Body water is weight × 0.6 for children and adult men, 0.5 for adult women and older men, and 0.45 for older women. Example: a 70 kg woman with sodium 118 has 35 L of body water, so 1 L of 3% saline (513 mmol/L) changes sodium by (513 − 118) ÷ 36 = +11.0 mmol/L, and 0.9% saline by +1.0.

The estimate assumes the whole litre stays in the body. Urine output, especially a water diuresis once the cause is corrected, can make the real rise much larger, so the measured sodium matters more than the prediction.

Correction limits quoted for comparison

The European clinical practice guideline on hyponatraemia (Spasovski G et al., Eur J Endocrinol 2014;170(3):G1–G47, recommendations 7.1.2.4 and 7.4.1.4) recommends limiting the increase to 10 mmol/L during the first 24 hours and 8 mmol/L during every 24 hours thereafter. Other guidelines, such as the US expert panel of Verbalis et al. (2013), set different figures for different risk groups — which is why the limit is an input you can change. The tool compares only the first 24 hours; assess later days separately.