Osmolar

Corrected sodium for hyperglycemia

Corrected sodium in hyperglycemia using the Katz (1.6) and Hillier (2.4) factors, with worked steps.

The calculator above returns two corrected sodium values side by side, one with the Katz factor (1.6) and one with the Hillier factor (2.4), each clearly labelled. This article explains why high glucose lowers the measured sodium, where the two factors come from, how to do the arithmetic by hand, and what a corrected sodium can and cannot tell you.

Looking for a hyponatremia correction rate? This is not that tool. Corrected sodium adjusts a lab value for the dilution caused by glucose. It gives no infusion rate, volume or fluid choice. Correction-rate decisions belong to the treating clinician.

Units. Glucose in mg/dL (US) or mmol/L (SI). Sodium in mEq/L, which equals mmol/L for a monovalent ion. Glucose mmol/L × 18 = mg/dL.

Why glucose lowers the measured sodium

Without enough insulin, glucose stays in the extracellular fluid and acts as an effective osmole. Merck notes that “because glucose does not penetrate cells in the absence of insulin, hyperglycemia further dehydrates the intracellular fluid (ICF) compartment” [5]. Water moves out of cells, which dilutes the extracellular sodium. The sodium falls even though total body sodium has not changed. StatPearls classifies hyperglycemia as a cause of hypertonic hyponatremia (serum osmolality above 295 mOsm/kg) [7].

That is why the measured sodium can mislead. The 2009 ADA consensus says “even normal serum sodium concentration in the presence of hyperglycemia indicates a rather profound degree of free water loss”, and it uses the corrected sodium “to assess the severity of sodium and water deficit” [3].

This is not pseudohyponatremia. Pseudohyponatremia is a measurement artefact: very high lipids or proteins reduce the water fraction of plasma, and an indirect ion-selective electrode then reads the sodium falsely low [8]. A glucose correction does not fix that. See Osmolality vs osmolarity for the plasma-water background.

The formula

Nacorrected (mmol/L) = Nameasured + k × (Glucose [mg/dL] − 100) ÷ 100

Factor kSourceBasis
1.6 mmol/L per 100 mg/dLKatz 1973 [1]A calculated estimate. Hillier calls it “the commonly used correction factor” [2]. The 2009 and 2024 ADA consensus documents use the same ratio [3, 4]
2.4 mmol/L per 100 mg/dLHillier 1999 [2]Experimental: 6 healthy volunteers, endogenous insulin blocked with somatostatin, glucose raised above 600 mg/dL with 20% dextrose. The mean fall was 2.4 mEq/L per 100 mg/dL
  • SI input: convert first (glucose mmol/L × 18), or use Na + k × (Gmmol/L − 5.55) ÷ 5.55.
  • Baseline: 100 mg/dL. At or below 100 mg/dL the correction is zero, so the corrected value equals the measured sodium. Below 100 the calculator adds the note “no correction applicable”. It never lowers the sodium.
  • Non-linearity: Hillier found the relationship non-linear. “Up to 400 mg/dL, the standard correction of 1.6 worked well, but if the glucose concentration was >400 mg/dL, a correction factor of 4.0 was better” [2]. The calculator flags glucose above 400 mg/dL but does not switch to 4.0, because that factor comes from a single study of 6 people.
  • Precision: the calculator keeps full precision and rounds only the displayed result, to 1 decimal place (half away from zero).

Worked example 1: US units

Measured Na 130 mmol/L, glucose 600 mg/dL.

  1. Excess glucose per 100 mg/dL: (600 − 100) ÷ 100 = 5
  2. Katz: 130 + 1.6 × 5 = 130 + 8 = 138.0 mmol/L
  3. Hillier: 130 + 2.4 × 5 = 130 + 12 = 142.0 mmol/L

The measured value falls below the 135–145 mmol/L adult reference interval [6]. Both corrected values fall inside it, which is consistent with the low reading being largely due to glucose.

Worked example 2: SI units

Measured Na 130 mmol/L, glucose 33.3 mmol/L.

  1. Convert: 33.3 × 18 = 599.4 mg/dL
  2. Excess: (599.4 − 100) ÷ 100 = 4.994
  3. Katz: 130 + 1.6 × 4.994 = 137.99 → 138.0 mmol/L
  4. Hillier: 130 + 2.4 × 4.994 = 141.99 → 142.0 mmol/L

Worked example 3: when the factors disagree

Measured Na 135 mmol/L, glucose 1,100 mg/dL.

  1. Excess: (1,100 − 100) ÷ 100 = 10
  2. Katz: 135 + 16 = 151.0 mmol/L. Hillier: 135 + 24 = 159.0 mmol/L

Both values are above the reference interval, so a “normal” measured sodium is hiding a water deficit [3]. The two estimates are 8 mmol/L apart, and the glucose is above 400 mg/dL, where Hillier found the relationship steeper still [2]. Report both, name each factor, and treat neither as exact.

Worked example 4: corrected sodium does not go into the osmolality formula

Same patient as example 1 (Na 130, glucose 600 mg/dL), BUN 28 mg/dL.

Osmolality formulas use the measured sodium. The ADA effective-osmolality definition is “2[measured Na+ (mEq/l)] + glucose (mg/dl)/18” [3].

  1. Glucose: 600 ÷ 18 = 33.33 mmol/L. BUN: 28 ÷ 2.8 = 10.0 mmol/L urea
  2. Calculated osmolality: 2 × 130 + 33.33 + 10.0 = 303.3 → 303 mOsm/kg
  3. Effective osmolality: 2 × 130 + 33.33 = 293.3 → 293 mOsm/kg

If you put the corrected sodium in, glucose gets counted twice. Urea is left out of the effective value because, as StatPearls puts it, “tonicity excludes urea because it freely crosses cell membranes” [7]. Use the serum osmolality calculator for this part.

Limitations

  • Two small evidence bases. Katz is a calculation. Hillier studied 6 healthy volunteers during acute, induced hyperglycemia [1, 2]. Patients with DKA or HHS also have osmotic diuresis, volume loss and treatment effects, which neither model includes.
  • Non-linear above 400 mg/dL [2]. The 1.6 factor probably underestimates the correction at high glucose.
  • Glucose only. Other effective osmoles that pull water out of cells, such as mannitol, are outside this formula.
  • Lab method. The formula assumes the measured sodium is accurate. It does not correct pseudohyponatremia from lipids or proteins [8].
  • A snapshot. As treatment lowers glucose, the measured sodium rises. The 2024 consensus uses the same ratio: a fall of 5.6 mmol/L (100 mg/dL) in glucose gives a 1.6 mmol/L rise in sodium [4]. Clinicians follow serial values. A single corrected number cannot do that.
  • No treatment output. The calculator never suggests fluids, rates or targets.

FAQs

Which factor should I use, 1.6 or 2.4? Both are published, and the calculator shows both. 1.6 is the traditional factor and is used in ADA consensus documents [3, 4]. Hillier’s experimental data support 2.4 as a better overall estimate, especially above 400 mg/dL [2]. Say which factor you used whenever you write the value down.

Can I correct sodium when glucose is normal or low? No correction is applied. At or below the 100 mg/dL baseline, the corrected value is the measured sodium.

Should the corrected sodium go into the serum osmolality formula? No. Calculated and effective osmolality use the measured sodium [3]. See worked example 4.

Is this the same as a hyponatremia correction-rate calculator? No. This page adjusts a lab value. How fast to change sodium, and with what, are clinical decisions made by the treating team.

Does a corrected sodium above 145 mmol/L mean hypernatremia? A high corrected value suggests water loss in excess of sodium [3]. Some hypernatremia work-ups recommend confirming the glucose-corrected sodium first [9]. The free water deficit calculator explains the next estimate, but its result is not a fluid order.

Educational content, not medical advice. Corrected sodium is an estimate for learning and lab interpretation. Correction-rate decisions, fluid choice and monitoring belong to the treating clinician. Verify against your institution’s protocols and your laboratory’s reference ranges. See our disclaimer and how we check content.

Related: Serum osmolality calculator · Free water deficit calculator · Isotonic, hypotonic, hypertonic · Osmolality vs osmolarity · Normal osmolality range · Osmolar gap · IV fluid osmolarity

References

  1. Katz MA. Hyperglycemia-induced hyponatremia—calculation of expected serum sodium depression. N Engl J Med. 1973;289(16):843–844. doi:10.1056/NEJM197310182891607. https://pubmed.ncbi.nlm.nih.gov/4763428/
  2. 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. https://pubmed.ncbi.nlm.nih.gov/10225241/
  3. 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. PMID 19564476. https://pmc.ncbi.nlm.nih.gov/articles/PMC2699725/
  4. Umpierrez GE, Davis GM, ElSayed NA, et al. Hyperglycemic crises in adults with diabetes: a consensus report. Diabetes Care. 2024;47(8):1257–1275. doi:10.2337/dci24-0032. PMID 39052901. PMC11272983. https://pmc.ncbi.nlm.nih.gov/articles/PMC11272983/ Simultaneously published in Diabetologia 2024;67(8):1455–1479, doi:10.1007/s00125-024-06183-8, PMID 38907161 (open full text PMC11343900).
  5. Merck Manual Professional Edition. Hypernatremia. https://www.merckmanuals.com/professional/nephrology/electrolyte-disorders/hypernatremia
  6. MedlinePlus Medical Encyclopedia. Sodium blood test. US National Library of Medicine. https://medlineplus.gov/ency/article/003481.htm
  7. Rout P, Afzal M. Hyponatremia. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK470386/ (PMID 29262111)
  8. Kim GH. Pseudohyponatremia: does it matter in current clinical practice? Electrolyte Blood Press. 2006;4(2):77–82. doi:10.5049/EBP.2006.4.2.77. https://pmc.ncbi.nlm.nih.gov/articles/PMC3894530/
  9. Yun G, Baek SH, Kim S. Evaluation and management of hypernatremia in adults: clinical perspectives. Korean J Intern Med. 2023;38(3):290–302. doi:10.3904/kjim.2022.346. https://pmc.ncbi.nlm.nih.gov/articles/PMC10175862/

Sources

Numbered references are listed in the article above.

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