1. What is Calculated Osmolality Blood Test?

Calculated osmolality is an estimate of the concentration of particles dissolved in blood plasma. It helps evaluate the body's water and electrolyte balance and can detect the presence of osmotically active substances like toxins or medications.

2. How Does the Calculator Work?

The calculator uses the osmolality formula:

Where:

• \( Osm \) — Calculated osmolality (mOsm/kg)
• \( Na \) — Sodium concentration (mEq/L)
• \( Glucose \) — Glucose concentration (mg/dL)
• \( BUN \) — Blood urea nitrogen concentration (mg/dL)

Explanation: The formula accounts for the major osmotically active particles in blood: sodium (and its accompanying anions), glucose, and urea.

3. Importance of Osmolality Calculation

Details: Osmolality calculation is important for assessing fluid and electrolyte balance, diagnosing dehydration or overhydration, evaluating renal function, and detecting osmolar gaps that may indicate the presence of toxins like alcohols or other osmotically active substances.

4. Using the Calculator

Tips: Enter sodium in mEq/L, glucose in mg/dL, and BUN in mg/dL. All values must be valid (sodium > 0, glucose and BUN ≥ 0).

5. Frequently Asked Questions (FAQ)

Q1: What is a normal osmolality range?
A: Normal serum osmolality ranges from 275 to 295 mOsm/kg. Values outside this range may indicate fluid and electrolyte imbalances.

Q2: What is an osmolar gap?
A: The osmolar gap is the difference between measured osmolality and calculated osmolality. A gap greater than 10 mOsm/kg suggests the presence of unmeasured osmotically active substances.

Q3: When should osmolality be measured?
A: Osmolality should be evaluated when assessing dehydration, electrolyte disorders, suspected alcohol intoxication, or unexplained metabolic acidosis.

Q4: Are there limitations to this calculation?
A: This calculation may not account for all osmotically active substances and may be less accurate in conditions with abnormal proteins or lipids in the blood.

Q5: How does osmolality relate to hydration status?
A: Increased osmolality typically indicates dehydration, while decreased osmolality may suggest overhydration or hyponatremia.