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Total Body Water by Mass Concentration (Serum/Plasma)

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

This test measures the amount of water present in your entire body, which helps assess hydration status and overall fluid balance.

Quick summary

["Understanding your body’s water content can help doctors diagnose dehydration, fluid overload, or other conditions."]

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

Key facts at a glance

LOINC
76637-8
Short code
Tot beats dur EKG
Synonyms
Tot beats dur EKG
Category
chemistry
Sample
serum
Container
Red-top tube (SST)
Units
N/A
Fasting
false
Population
adult
Sex
all
Age range
18–65 years
Method
ekg
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 Is This Test Done?

Your healthcare provider may order this test if you have symptoms like excessive thirst, fatigue, confusion, or swelling. It’s also used in certain medical conditions, such as kidney disease or heart failure, where fluid balance is critical.

How Is the Test Performed?

A small blood sample is drawn from a vein, usually in your arm. The blood is then analyzed to estimate total body water content using specialized methods.

What Do the Results Mean?

Results are not provided in absolute units but are used relative to your body composition and clinical context. Lower than expected levels may indicate dehydration, while higher levels could suggest fluid retention or other conditions.

Common Conditions Affecting Results

Conditions like kidney disease, heart failure, or severe illness can influence total body water. Age, body composition, and medications may also play a role.

Clinical interpretation

How abnormal results are interpreted and what conditions they suggest.

◆Associated findings1

Short name

Total Body Water (TBW)

Frequently asked questions

What causes abnormal total body water levels?
Abnormal levels can result from dehydration (too little water), fluid overload (too much water), kidney or heart problems, or certain medications. Symptoms like dizziness, swelling, or rapid breathing may indicate an imbalance.
How often should I get this test?
Your doctor will determine how often this test is needed based on your health condition, symptoms, and treatment plan. It may be part of routine check-ups or monitoring for specific medical issues.
Can diet or lifestyle affect this test?
Dietary habits, hydration status, and lifestyle factors like exercise can influence fluid balance, but this test measures total body water rather than recent fluid intake. Your doctor will consider these factors when interpreting results.
  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