Corrected Sodium Calculator

Formula: Corrected Na = Measured Na + 0.016 × (Glucose – 100). Each 100 mg/dL increase in glucose above 100 lowers serum sodium by approximately 1.6 mEq/L. For glucose in mmol/L: use 0.016 × (Glucose – 5.6).

Pseudohyponatremia is a falsely low measured sodium due to hyperglycemia, hyperlipidemia, or hyperproteinemia. The corrected sodium formula accounts for the glucose effect. True hyponatremia requires evaluation of volume status and ADH regulation.

Normal serum sodium is 135–145 mEq/L. Hyponatremia is defined as Na < 135 mEq/L. Hypernatremia is Na > 145 mEq/L. Severe hyponatremia is Na < 120 mEq/L. Severe hypernatremia is Na > 160 mEq/L.

Mild (Na 130–134): headache, nausea, confusion. Moderate (Na 125–129): vomiting, lethargy, muscle cramps. Severe (Na < 125): seizures, coma, respiratory arrest, brainstem herniation. Rapid correction can cause osmotic demyelination syndrome (ODS).

FWD estimates the volume of free water needed to correct hypernatremia. Formula: FWD (L) = 0.6 × Weight (kg) × (1 – 140/Na). For a 70 kg patient with Na 155: FWD = 0.6 × 70 × (1 – 140/155) = 42 × 0.097 = 4.1 L.

Maximum correction: 8–12 mEq/L in 24 hours. In severe symptomatic hyponatremia, a 4–6 mEq/L increase in the first 4 hours is acceptable to alleviate symptoms. Exceeding 8 mEq/L in 24 hours risks osmotic demyelination syndrome (ODS).

ODS (formerly central pontine myelinolysis) is a neurological disorder caused by rapid correction of hyponatremia. Symptoms appear 2–5 days after correction: dysarthria, dysphagia, quadriparesis, locked-in syndrome. Prevention: limit correction to < 8 mEq/L/24h.

Risk factors: chronic hyponatremia (> 48h duration), alcoholism, liver disease (cirrhosis), malnutrition, hypokalemia, diuretic use, post-surgical state, and a starting Na < 120 mEq/L. These patients need ultra-conservative correction (< 6–8 mEq/L/24h).

Correct by replacing the free water deficit. Use D5W or 0.45% NS (half-normal saline). Replace half of the FWD over the first 24 hours, the remainder over the next 24–48 hours. Do not exceed a correction rate of 10–12 mEq/L/24h to prevent cerebral edema.

FWD (L) = 0.6 × Weight (kg) × (1 – 140/Na). Use 0.5 for women instead of 0.6. For a 50 kg woman with Na 160: FWD = 0.5 × 50 × (1 – 140/160) = 25 × 0.125 = 3.125 L. Replace over 48–72 hours.

Correction rate (mEq/L/hr) = (Current Na – Target Na) / Time (hr). For hypernatremia: target Na = 140. For a Na of 155 corrected over 24 hours: (155–140)/24 = 0.625 mEq/L/hr (within safe limit of 0.5 mEq/L/hr).

Maximum 0.5 mEq/L/hr or 10–12 mEq/L/24h. Faster correction can cause cerebral edema. In chronic hypernatremia (> 48h), even slower correction (0.3–0.4 mEq/L/hr) is recommended. Monitor sodium every 2–4 hours during active correction.

Measured sodium is the laboratory value. Corrected sodium adjusts for the dilutional effect of hyperglycemia using the formula: Corrected Na = Measured Na + 0.016 × (Glucose – 100). This gives the true sodium level if the glucose were normal.

Glucose is an osmotically active molecule that draws water into the extracellular space, diluting sodium. Each 100 mg/dL rise in glucose reduces measured sodium by ~1.6 mEq/L. This is a dilutional hyponatremia, not true hyponatremia.

Yes, corrected sodium is essential in DKA as hyperglycemia (300–600+ mg/dL) significantly lowers measured Na. The corrected Na reveals the true sodium, often uncovering relative hypernatremia requiring careful rehydration.

Give 3% hypertonic saline (2–4 mL/kg IV over 10–20 minutes) for severe symptoms (seizures, coma). Goal: 4–6 mEq/L increase in first 4 hours. Stop once symptoms resolve. Then switch to slower correction with NS or 0.45% NS.

Identify and reverse the cause: stop thiazide diuretics, treat SIADH with fluid restriction (500–1000 mL/day) or vasopressin antagonists (tolvaptan, conivaptan). In hypovolemic hyponatremia, give NS 0.9% to correct volume depletion.

SIADH causes water retention and dilutional hyponatremia due to excess ADH. Common causes: CNS disorders, pulmonary diseases (pneumonia, TB), malignancy (SCLC), medications (SSRIs, carbamazepine). Treatment: fluid restriction, vasopressin antagonists.

3% hypertonic saline (513 mEq/L Na) is used for severe symptomatic hyponatremia. Give 2–4 mL/kg IV over 10–20 minutes. Repeat until symptoms resolve or Na rises by 4–6 mEq/L. Must be given in ICU setting with frequent Na monitoring.

Hypovolemic hyponatremia: volume depleted (diarrhea, diuretics, vomiting). Euvolemic: normal volume (SIADH, polydipsia, hypothyroidism). Hypervolemic: edematous (CHF, cirrhosis, nephrotic syndrome). Check urine Na and osmolality to distinguish causes.

Urine Na > 20–40 mEq/L with urine osmolality > 100 mOsm/kg (inappropriately concentrated urine despite hyponatremia). FENa > 1%. Urine osmolality > plasma osmolality. Low uric acid and BUN due to volume expansion.

Hypokalemia worsens hyponatremia. Correct K+ before or during Na correction because as K+ is replaced, it shifts into cells and draws Na+ out (K+ is an effective osmole). Uncorrected hypokalemia can lead to overcorrection when K+ is repleted.

The Adrogue-Madias formula estimates the change in serum Na per liter of infusate: ΔNa = (Infusate Na + Infusate K – Serum Na) / (Total Body Water + 1). It helps predict the sodium change with different IV fluids (3% NS, NS, D5W).

Using Adrogue-Madias: ΔNa = (513 – Current Na) / (TBW + 1). TBW = 0.6 × Wt (men) or 0.5 × Wt (women). For a 70 kg man with Na 120: (513–120)/(42+1) = 393/43 = 9.1 mEq/L increase per liter of 3% NS. This is an approximation.

True hyponatremia has low measured Na due to excess water relative to sodium (hypotonic hyponatremia). Pseudohyponatremia has low measured Na but normal or high true Na after correcting for glucose, lipids, or proteins. Only true hyponatremia requires treatment.

Check serum Na every 2–4 hours during active correction. In the first 24 hours, check Na at: baseline, 2h, 4h, 8h, 12h, and 24h. More frequent checks in severe cases. Stop active correction if Na has risen by 8 mEq/L, even if still below normal.

DDAVP (synthetic ADH) is used to prevent overcorrection of hyponatremia. If Na rises too fast (> 8 mEq/L/24h), DDAVP 1–2 mcg IV can be given to temporarily reduce free water excretion and prevent continued rapid rise.

Use 0.5 instead of 0.6 for the TBW fraction. FWD (L) = 0.5 × Weight (kg) × (1 – 140/Na). For a 60 kg woman with Na 150: 0.5 × 60 × (1 – 140/150) = 30 × 0.067 = 2.0 L. Replace half over 24h (1 L in 24h = 42 mL/hr D5W).

Children are at lower but still significant risk of ODS. The same correction limits apply (8 mEq/L/24h). Use D5 1/2NS for deficit replacement in children. 3% saline (2–4 mL/kg) is used for symptomatic hyponatremia with seizures.

Malnutrition reduces TBW fraction. Use 0.5 for both genders in severe malnutrition. Protein depletion reduces urea, which acts as an osmole. These patients have high ODS risk due to intracellular osmole depletion. Correct even more slowly (6 mEq/L/24h max).