Corrected Sodium Calculator for Hyperglycemia (Katz, Hillier)

Correct a measured sodium for hyperglycaemia with both the Katz and Hillier factors, with glucose in mg/dL or mmol/L and the working shown. For healthcare professionals.

How to use it

Enter the measured serum sodium in mmol/L (the same number as mEq/L).
Enter the blood glucose and pick mg/dL or mmol/L.
Read the corrected sodium by Hillier (2.4) and Katz (1.6), with the working below.

Formulas

Katz: corrected Na = measured Na + 1.6 × (glucose − 100) ÷ 100
Hillier: corrected Na = measured Na + 2.4 × (glucose − 100) ÷ 100
with glucose in mg/dL (mmol/L × 18.016). Hillier and colleagues found 4.0 a better factor when glucose is over 400 mg/dL.

Worked example

Sodium 130 mmol/L with glucose 600 mg/dL (33.3 mmol/L) is 500 mg/dL above 100: Hillier gives 130 + 2.4 × 5 = 142 mmol/L and Katz 130 + 1.6 × 5 = 138 mmol/L. With Hillier's 4.0 factor for glucose over 400 it would be 150 mmol/L.

Quick reference: measured sodium 135 mmol/L

How much the correction adds grows in a straight line with glucose. For a measured sodium of 135 mmol/L, the two factors give these corrected values (worked out by this calculator):

Glucose (mg/dL)	Glucose (mmol/L)	Katz (1.6)	Hillier (2.4)
100	5.6	135.0	135.0
200	11.1	136.6	137.4
300	16.7	138.2	139.8
400	22.2	139.8	142.2
600	33.3	143.0	147.0
800	44.4	146.2	151.8
1000	55.5	149.4	156.6

Why the two factors differ

Katz derived 1.6 mmol/L per 100 mg/dL in 1973 from a theoretical model of water moving out of cells. Hillier and colleagues tested it in 1999 by raising glucose in healthy volunteers and measuring the sodium fall directly: the average was 2.4, and the relationship wasn't linear, fitting 1.6 below about 400 mg/dL and 4.0 above it. That's why the gap between the two results widens as glucose rises, and why some references quote a range rather than one corrected number.

References

Katz MA. Hyperglycemia-induced hyponatremia: calculation of expected serum sodium depression. N Engl J Med 1973;289:843–844 (PMID 4763428).
Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med 1999;106:399–403 (PMID 10225241).

Formulas checked on 7 October 2026. For professionals: verify against current guidelines; this is not medical advice.

Frequently asked questions

Why does high glucose lower the measured sodium?

Glucose stays outside cells and draws water out of them, which dilutes the sodium in the blood. The corrected value estimates what the sodium would be if the glucose came down to normal (100 mg/dL), so the dilution can be told apart from a true sodium disorder.

Katz or Hillier: which factor should I use?

Katz (1973) worked out a fall of 1.6 mmol/L for every 100 mg/dL rise in glucose. Hillier and colleagues (1999) measured it in volunteers and found an average of 2.4, and noted that 1.6 worked up to about 400 mg/dL while 4.0 fitted better above that. Many references now quote 2.4; the calculator shows both, plus the 4.0 figure when glucose is over 400 mg/dL.

My glucose is in mmol/L. Does that work?

Yes. Switch the glucose unit: the calculator multiplies by 18.016 (glucose's molar mass is 180.16 g/mol) to get mg/dL. Per mmol/L, the factors are about 0.29 (Katz) and 0.43 (Hillier) mmol/L of sodium for each mmol/L of glucose above 5.55.

What if glucose is normal or low?

There's nothing to correct for: at 100 mg/dL (5.55 mmol/L) or below, the corrected sodium equals the measured value.

Can this tell me how to treat the patient?

No. It's the arithmetic of published correction factors for professionals to check, not guidance on fluids, insulin or electrolytes.

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