Enter the sodium, glucose, and BUN values into the calculator to determine your serum osmolality.

Serum Osmolality Calculation Formula

The following formula is used to calculate serum osmolality.

Osmolality = 2 * Na + Glucose / 18 + BUN / 2.8

Variables:

  • Osmolality is the calculated serum osmolality (mOsm/kg)
  • Na is the concentration of sodium in the blood (mmol/L)
  • Glucose is the concentration of glucose in the blood (mg/dL)
  • BUN is the concentration of blood urea nitrogen (mg/dL)

To calculate the serum osmolality, multiply the sodium concentration by 2, add the glucose concentration divided by 18, and add the BUN concentration divided by 2.8.

What is Serum Osmolality?

Serum osmolality is a measure of the solute concentration in the blood. It is a key indicator of the body’s fluid balance and the ability of the kidneys to concentrate urine. The normal range for serum osmolality is typically between 275 and 295 mOsm/kg. Deviations from this range can indicate various medical conditions, including dehydration, kidney dysfunction, or metabolic imbalances.

How to Calculate Serum Osmolality?

The following steps outline how to calculate the serum osmolality using the given formula:

  1. Determine the concentration of sodium in the blood (Na).
  2. Determine the concentration of glucose in the blood.
  3. Determine the concentration of blood urea nitrogen (BUN).
  4. Use the formula: Osmolality = 2 * Na + Glucose / 18 + BUN / 2.8.
  5. Calculate the serum osmolality by plugging in the values.
  6. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem:

Use the following variables as an example problem to test your knowledge.

Sodium (Na) = 140 mmol/L

Glucose = 90 mg/dL

BUN = 15 mg/dL

FAQ

1. What is serum osmolality?

Serum osmolality is the measure of solute concentration in the blood, indicating the body’s fluid balance.

2. How is serum osmolality calculated?

Serum osmolality is calculated using the formula: Osmolality = 2 * Na + Glucose / 18 + BUN / 2.8.

3. What are normal serum osmolality levels?

Normal serum osmolality levels range between 275 and 295 mOsm/kg.

4. Why is serum osmolality important?

Serum osmolality is important for assessing fluid balance and kidney function, and for diagnosing conditions like dehydration and metabolic imbalances.

5. Can this calculator be used for different patient conditions?

Yes, this calculator can be used to assess serum osmolality for various conditions by adjusting the input values accordingly.

6. Is the calculator accurate?

The calculator provides an estimate of serum osmolality based on the inputs provided. For precise measurements, consult a healthcare professional.