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Freezing Point of Plasma (or Serum) – Osmolality Measurement

Published: August 9, 2026Updated: August 16, 2026

This test measures the concentration of dissolved substances in your blood, helping assess how well your body balances water and electrolytes.

Quick summary

["Osmolality helps detect dehydration, kidney function issues, or metabolic imbalances."]

Medically reviewed by WellAlly Editorial TeamLast reviewed August 16, 2026Editorial policy

Key facts at a glance

LOINC
20824-9
Short code
Freezing Pnt Mlk
Synonyms
Freezing Pnt Mlk
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Ref low
3.5
Ref high
5
Critical range
2.5 N/A – 6.5 N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
CPT
84132
SNOMED
110742001
Specimen volume
5 mL
Stability
Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
Hemolysis max
500
Lipemia max
1000
Icterus max
500
TAT
4–24 hours
Order
routine

Why It’s Done

Your doctor may order this test if you have symptoms like extreme thirst, confusion, swelling, or unexplained weight changes. It’s also used to monitor conditions like diabetes, kidney disease, or severe infections.

What to Expect

A small blood sample is drawn from your arm. The sample is sent to a lab where it’s analyzed to determine its freezing point, which reflects dissolved particle count.

Common Reasons for Testing

Osmolality checks are often part of broader evaluations for dehydration, electrolyte disorders, or conditions affecting fluid balance in the body.

How Results Are Interpreted

Results are compared to a standard range, though exact values can vary by lab. High osmolarity may suggest dehydration or diabetes, while low values could indicate overhydration or kidney problems.

Reference range

Adult: 3.5-5.0 mmol/LN/A

Specimen: serum

No special preparation usually required. Stay well hydrated. Inform your healthcare provider of all medications and supplements you are taking.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Plasma Osmolality

Frequently asked questions

What causes high plasma osmolarity?
High osmolarity often results from dehydration (e.g., from vomiting, diarrhea, or insufficient water intake), diabetes insipidus, or excessive use of diuretics. It may also appear in severe infections or heatstroke.
What causes low plasma osmolarity?
Low osmolarity can occur with overhydration (e.g., kidney failure, excessive IV fluids), hyponatremia (low sodium), or certain medications like thiazide diuretics.
Does diet affect osmolarity results?
Dietary factors like salt intake or sugar consumption can indirectly influence osmolarity, but the test itself measures dissolved particles, not specific nutrients. Avoid extreme fluid restriction or overhydration before testing if advised by your doctor.
  1. 1
    MedlinePlus — Laboratory TestsSource
  2. 2
    Lab Tests OnlineSource
  3. 3
    Mayo Clinic — Tests & ProceduresSource

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.

Medical Disclaimer

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