Chemistry
Sodium Correction for Hyperglycaemia
Corrected sodium in hyperglycaemia (Katz).
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Background
This calculation estimates a patient's true (corrected) serum sodium when it has been artificially lowered by hyperglycaemia. High blood glucose draws water out of cells into the bloodstream, diluting the measured sodium and producing a translocational (dilutional) pseudohyponatraemia. The Katz correction adds 1.6 mmol/L to the measured sodium for every 100 mg/dL that glucose exceeds 100 mg/dL. It is used in diabetic emergencies such as diabetic ketoacidosis (DKA) and the hyperosmolar hyperglycaemic state (HHS).
Interpreting the result
The corrected sodium estimates what the sodium would be once glucose is normalised, revealing the underlying sodium state masked by hyperglycaemia. A corrected sodium that is normal or high, despite a low measured value, indicates the patient is not truly hyponatraemic and may be significantly water-depleted, which guides fluid choice. Watching the corrected sodium as glucose falls helps anticipate and avoid rapid osmolar shifts during treatment.
Worked example
A patient in HHS has a measured sodium of 130 mmol/L and a glucose of 1000 mg/dL. Glucose is 900 mg/dL above 100, so the correction adds about 9 × 1.6 ≈ 14 mmol/L, giving a corrected sodium of roughly 144 mmol/L — revealing that the apparent hyponatraemia masks marked hypertonicity and water deficit.
Critical actions
This uses the Katz factor (1.6 mmol/L per 100 mg/dL above 100). Enter glucose in mg/dL (multiply mmol/L by 18). Some use the Hillier factor of 2.4.
Pearls / pitfalls
- Enter glucose in mg/dL — multiply a value in mmol/L by 18 first, or the correction will be wrong.
- The result is an estimate; the Hillier factor of about 2.4 may fit better at very high glucose, so interpret the number as a guide.
- It addresses translocational hyponatraemia only — it does not explain a low sodium with normal glucose, which needs separate evaluation.
- In DKA and HHS, follow the specific treatment protocol; use the corrected sodium to inform fluid choices and watch for over-rapid changes, not to replace the protocol.
Evidence & validation
The classic correction factor of 1.6 mmol/L per 100 mg/dL was described by Katz in 1973. Later experimental work by Hillier and colleagues suggested a larger factor of around 2.4, particularly at very high glucose levels; both are used in practice, and the corrected value is best treated as an estimate to inform, not dictate, management.
Frequently asked questions
Why does high glucose lower the measured sodium?
Glucose is osmotically active and pulls water from inside cells into the blood, diluting the sodium. This produces a falsely low measured sodium, known as translocational or dilutional pseudohyponatraemia.
What units should glucose be entered in?
This calculation uses mg/dL with the Katz factor of 1.6 per 100 mg/dL above 100. If your glucose is in mmol/L, multiply by about 18 to convert before entering it.
Should I use the Katz factor of 1.6 or the Hillier factor of 2.4?
Both are used. The 1.6 factor is the classic correction, while 2.4 may better reflect reality at very high glucose. Treat the corrected value as an estimate to guide, not dictate, decisions.
What does a normal corrected sodium with low measured sodium tell me?
It indicates the patient is not truly hyponatraemic; the low measured value reflects dilution by glucose. Such patients are often significantly water-depleted, which informs fluid therapy.
Does correcting the glucose fix the sodium?
Largely yes — as glucose falls with treatment, water shifts back into cells and the measured sodium tends to rise towards the corrected value. Monitoring this helps avoid over-rapid osmolar shifts.
References
- Katz MA. Hyperglycemia-induced hyponatremia — calculation of expected serum sodium depression. N Engl J Med. 1973;289(16):843–844.
- Hillier TA, Abbott RD, Barrett EJ. Hyponatremia: evaluating the correction factor for hyperglycemia. Am J Med. 1999;106(4):399–403.
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