Corrected sodium for hyperglycemia: how to calculate it with the Katz or Hillier factor

Corrected sodium adds an amount to the measured sodium for each 100 mg/dL that glucose is above 100 mg/dL. The amount per 100 mg/dL is a published factor: 1.6 (Katz) or 2.4 (Hillier). For a measured sodium of 125 mmol/L and a glucose of 400 mg/dL, the Katz result is 125 + 1.6 × 3.0 = 129.8 mmol/L.

Not a medical device. Not a diagnosis or dosing recommendation.

Use this calculator via API

What is corrected sodium?

High blood glucose lowers the measured serum sodium concentration.[3] Published clinical references note that most low sodium readings are hypotonic, and list hyperglycemia among the exceptions.[1] The corrected sodium is a calculation that puts back the expected fall, using a fixed amount for every 100 mg/dL of glucose.

Magent supports two published factors, and they give different answers for the same patient. Magent's calculator makes you choose one: formula=katz applies 1.6, and formula=hillier applies 2.4. It doesn't pick one for you.

This page explains the arithmetic. It doesn't give a normal range, and it doesn't recommend one factor over the other.

The corrected sodium formula

Katz:    corrected_na_mmol_l = sodium_mmol_l + 1.6 * (glucose_mg_dl - 100) / 100
Hillier: corrected_na_mmol_l = sodium_mmol_l + 2.4 * (glucose_mg_dl - 100) / 100

Exact expression the calculator uses:

katz (1.6): corrected_na_mmol_l = sodium_mmol_l + 1.6 * (glucose_mg_dl - 100) / 100. hillier (2.4): corrected_na_mmol_l = sodium_mmol_l + 2.4 * (glucose_mg_dl - 100) / 100. Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999;106(4):399-403. DOI 10.1016/S0002-9343(99)00055-8.

In words: take glucose minus 100, divide by 100, multiply by the chosen factor, and add the result to the measured sodium. Magent's calculator reports the result to 1 decimal place.

What each part means

Term	Plain-English meaning	Unit	Accepted range
`sodium_mmol_l`	Measured serum sodium	mmol/L	110–160
`glucose_mg_dl`	Plasma glucose	mg/dL	50–1000
`glucose_mmol_l`	Plasma glucose, if you have it in SI units	mmol/L	2.8–55.5
`formula`	Which published factor to apply	`katz` (1.6) or `hillier` (2.4)	required
`corrected_na_mmol_l`	Corrected sodium	mmol/L	1 decimal place

You give glucose one way or the other, in mg/dL or in mmol/L.

How the formula works

Put glucose in mg/dL. If you have mmol/L, multiply by 18.015.
Subtract 100 from the glucose, then divide by 100. This is the number of 100 mg/dL steps above 100.
Multiply by the chosen factor: 1.6 for Katz or 2.4 for Hillier.
Add the result to the measured sodium.
Round to 1 decimal place.

At a glucose of exactly 100 mg/dL, nothing is added and the corrected sodium equals the measured sodium. Each further 100 mg/dL adds 1.6 mmol/L with Katz or 2.4 mmol/L with Hillier, so the gap between the two results grows by 0.8 mmol/L for every 100 mg/dL. The accepted glucose range starts at 50 mg/dL, and below 100 mg/dL the same arithmetic subtracts a small amount instead.

Units and conversions

Sodium is entered and reported in mmol/L. Glucose in mmol/L is converted with mg/dL = mmol/L × 18.015 before the formula runs, so 20.0 mmol/L becomes 360.3 mg/dL. The factors are defined per 100 mg/dL of glucose, which is why the calculator converts to mg/dL first.

Worked examples

These use Magent's own expected values for the calculator.

Example 1: sodium 125, glucose 400 mg/dL, Katz

Steps above 100: (400 − 100) ÷ 100 = 3.0
Amount added: 1.6 × 3.0 = 4.8
Corrected sodium: 125 + 4.8 = 129.8 mmol/L

Example 2: the same inputs, Hillier

Steps above 100: 3.0
Amount added: 2.4 × 3.0 = 7.2
Corrected sodium: 125 + 7.2 = 132.2 mmol/L

Examples 1 and 2 use identical inputs. Choosing the factor changes the answer by 2.4 mmol/L.

Example 3: glucose given in mmol/L, Katz

Glucose: 20.0 × 18.015 = 360.3 mg/dL
Steps above 100: (360.3 − 100) ÷ 100 = 2.603
Amount added: 1.6 × 2.603 = 4.1648
Corrected sodium: 125 + 4.1648 = 129.1648, rounded to 129.2 mmol/L

Example 4: sodium 140, glucose 100 mg/dL, Katz

Steps above 100: (100 − 100) ÷ 100 = 0
Corrected sodium: 140 + 0 = 140.0 mmol/L

Corrected sodium reference table

These values are computed from both formulas and rounded to 1 decimal, as Magent's calculator reports them. The result columns use a measured sodium of 130 mmol/L; for any other measured value, add the "adds" column to it. They show how the correction moves; they aren't targets, reference ranges or categories.

Glucose (mg/dL)	Katz adds (×1.6)	Katz result, measured Na 130	Hillier adds (×2.4)	Hillier result, measured Na 130
50	−0.8	129.2	−1.2	128.8
100	0.0	130.0	0.0	130.0
200	+1.6	131.6	+2.4	132.4
300	+3.2	133.2	+4.8	134.8
400	+4.8	134.8	+7.2	137.2
600	+8.0	138.0	+12.0	142.0
800	+11.2	141.2	+16.8	146.8
1000	+14.4	144.4	+21.6	151.6

At 50 mg/dL the amount is negative, because glucose is below 100 mg/dL.

History of the correction factors

The 1.6 factor comes from M. A. Katz, Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression, published in the New England Journal of Medicine in 1973 (volume 289, issue 16, pages 843–844). PubMed and Europe PMC list no abstract for it, and its full text wasn't read for this page.

The 2.4 factor comes from T. A. Hillier, R. D. Abbott and E. J. Barrett, Hyponatremia: evaluating the correction factor for hyperglycemia, published in the American Journal of Medicine in 1999 (volume 106, issue 4, pages 399–403). Its abstract says there were no controlled experimental data on the accuracy of the commonly used 1.6 factor.[2] The authors raised plasma glucose in 6 healthy volunteers with a dextrose infusion while insulin secretion was blocked, and measured sodium and glucose every 10 minutes. The mean fall in sodium averaged 2.4 meq/L for every 100 mg/dL rise in glucose, and the authors described the relationship as nonlinear.[2] They concluded that 2.4 was a better overall estimate than 1.6.[2]

Magent's calculator applies a single straight-line factor across the whole accepted glucose range, whichever formula you choose.

When it's used

The correction applies when glucose is high and the measured sodium is being read alongside it. Published references list hyperglycemia among the exceptions to the usual hypotonic pattern of low sodium.[1] A 2020 study compared measured and corrected sodium in adults with severe hyperglycemia.[3]

Where it's used

That 2020 study enrolled adults with severe hyperglycemia who came to an emergency department, and it applied the 2.4 factor.[3] The inputs are a routine sodium and glucose from the same blood sample.

Who uses it

The sources cited here are a clinical reference chapter, the original factor papers and one emergency department cohort. They don't single out one professional group, so this page doesn't name one.

Limits of the calculation

It's arithmetic for the factor you choose. Choosing the factor is required; Magent's calculator doesn't pick Katz or Hillier.
It doesn't label a sodium value as high, low or normal.
It doesn't suggest fluids, insulin or any other care.
It applies one straight-line factor. Hillier and colleagues described the real relationship as nonlinear.[2]
Inputs outside the accepted ranges are rejected, not estimated.

Clinical decisions belong to a qualified clinician who knows the patient.

How it differs from related calculators

Corrected calcium adjusts total calcium for albumin with the Payne formula. It corrects a different electrolyte for a different protein.
A1C ↔ eAG converts an A1C percentage to estimated average glucose, or the reverse. It doesn't touch sodium.
Bicarbonate deficit estimates a bicarbonate deficit from weight and measured plasma bicarbonate.
Katz versus Hillier. Both use the same structure. The factor is the difference: 1.6 or 2.4 mmol/L per 100 mg/dL of glucose.

Glossary

Measured sodium: the serum sodium as reported by the laboratory, in mmol/L.
Corrected sodium: measured sodium plus a published amount for each 100 mg/dL of glucose above 100 mg/dL.
Katz factor: 1.6 mmol/L per 100 mg/dL of glucose (1973).
Hillier factor: 2.4 mmol/L per 100 mg/dL of glucose (1999).
Hyperglycemia: high blood glucose.
18.015: the factor used here to convert glucose from mmol/L to mg/dL.

Common mistakes

Not stating the factor. Katz and Hillier give different answers, so record which one was used.
Mixing glucose units. The factors are per 100 mg/dL. Convert mmol/L glucose first, or enter it as glucose_mmol_l.
Forgetting to subtract 100. The correction counts steps above 100 mg/dL, not the whole glucose value.
Rounding early. Keep full precision through the steps, then round once at the end.

Source

Katz MA. Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression. N Engl J Med. 1973;289(16):843-844. DOI: 10.1056/NEJM197310182891607

Frequently asked questions

How do you correct sodium for glucose?

Subtract 100 from the glucose in mg/dL, divide by 100, multiply by the chosen factor (1.6 or 2.4), and add the result to the measured sodium. For sodium 125 and glucose 400 with Katz, that's 125 + 1.6 × 3.0 = 129.8 mmol/L.

What is the Katz correction factor?

It's 1.6 mmol/L of sodium for every 100 mg/dL of glucose above 100 mg/dL, from Katz's 1973 paper.

What is the Hillier 2.4 factor?

It's 2.4 mmol/L of sodium for every 100 mg/dL of glucose above 100 mg/dL. It comes from a 1999 study in healthy volunteers.[2]

Should I use Katz or Hillier?

This page doesn't recommend one. Magent's calculator requires you to choose, and the history section above describes where each factor comes from.

What is a normal corrected sodium?

This page doesn't give a normal range. It calculates the corrected value; what a value means depends on the laboratory and the clinical context.

Can I enter glucose in mmol/L?

Yes. Use glucose_mmol_l. It's converted with mg/dL = mmol/L × 18.015, so 20.0 mmol/L is 360.3 mg/dL.