Calculated Serum Osmolality Calculator

Calculated Serum Osmolality Formula:

\[ O_{serum} = (2 \times [Na]_{serum}) + \left(\frac{G_{serum}}{18}\right) + \left(\frac{BUN}{2.8}\right) \]

Calculated Serum Osmolality:

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1. What is Calculated Serum Osmolality?

Calculated Serum Osmolality refers to the calculated concentration of dissolved particles of chemicals and minerals such as sodium and other electrolytes in given serum. It is an important clinical measurement used to assess the body's water-electrolyte balance.

2. How Does the Calculator Work?

The calculator uses the formula:

\[ O_{serum} = (2 \times [Na]_{serum}) + \left(\frac{G_{serum}}{18}\right) + \left(\frac{BUN}{2.8}\right) \]

Where:

\( [Na]_{serum} \) — Serum Sodium concentration (mEq/L)
\( G_{serum} \) — Serum Glucose concentration (mg/dL)
\( BUN \) — Blood Urea Nitrogen concentration (mg/dL)

Explanation: This formula calculates the osmotic concentration of particles in the blood serum, primarily driven by sodium ions, glucose, and urea.

3. Importance of Serum Osmolality Calculation

Details: Serum osmolality measurement is crucial for diagnosing and monitoring conditions such as dehydration, diabetes insipidus, syndrome of inappropriate antidiuretic hormone secretion (SIADH), and toxic alcohol poisoning.

4. Using the Calculator

Tips: Enter serum sodium in mEq/L, serum glucose in mg/dL, and blood urea nitrogen in mg/dL. All values must be valid positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What is the normal range for serum osmolality?
A: Normal serum osmolality ranges from 275 to 295 mOsm/kg. Values outside this range may indicate underlying medical conditions.

Q2: Why is sodium multiplied by 2 in the formula?
A: Sodium is multiplied by 2 because each sodium ion is accompanied by an anion (usually chloride), effectively doubling its osmotic contribution.

Q3: When should serum osmolality be measured?
A: It should be measured when evaluating fluid and electrolyte disorders, altered mental status, suspected toxic ingestions, or monitoring treatment response in related conditions.

Q4: Are there limitations to this calculation?
A: This calculation may not account for other osmotically active substances such as ethanol, methanol, ethylene glycol, or mannitol that may be present in certain clinical situations.

Q5: What is the osmolar gap?
A: The osmolar gap is the difference between measured osmolality and calculated osmolality. An increased gap (>10 mOsm/kg) may indicate the presence of unmeasured osmotically active substances.