Osmolarity of Serum (Plasma) (Total)
This test measures the total concentration of dissolved particles (solutes) in your blood, helping assess hydration and kidney function.
["Osmolarity helps diagnose dehydration, kidney issues, or fluid imbalances."]
Key facts at a glance
- LOINC
- 18493-7
- Short code
- O+P sp3 Stl Conc
- Synonyms
- O+P sp3 Stl Conc
- Category
- chemistry
- Sample
- stool
- Container
- Clean container
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- concentration
- Specimen volume
- 5 g
- Stability
- Refrigerated: 24h, Frozen: 7d
- TAT
- 4–24 hours
- Order
- routine
Why It Matters in Health
Osmolarity reflects the balance of water and solutes in your blood. Too high or too low levels can signal problems like dehydration, kidney disease, or excessive fluid retention.
How It’s Performed
A blood sample is taken from a vein, usually in your arm. The lab then measures the total concentration of solutes in the serum or plasma using specialized equipment.
What to Expect Before the Test
No special preparation is needed, but inform your provider if you’re on certain medications or have conditions like kidney disease.
Common Conditions Monitored
Osmolarity is often checked in cases of suspected dehydration, kidney problems, or fluid imbalances, such as those seen in diabetes or heart failure.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Abnormally high osmolarity may indicate dehydration, diabetes insipidus, or excessive use of diuretics. Abnormally low osmolarity could signal overhydration, kidney failure, or certain liver conditions. Always discuss results with your healthcare provider for personalized interpretation.
Short name
Serum Osmolarity
Frequently asked questions
What causes abnormal osmolarity results?
How long does it take to get results?
Can I drink water before this test?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy