Stable Isotope Research Applications

Stable Isotope Assays for Total Body Water & Fluid Volume Measurement

We provide administration kits, project design support, and stable isotope analysis using D₂O and 18O tracers to help researchers determine total body water (TBW) and fluid volume homeostasis. We deliver accurate measurements from just 15–25 µl of plasma, urine, or saliva.

Trusted by Pharma and Biotech to Validate Mechanism of Action

Pfizer_logo
Merck_Logo.svg
Novartis-Logo.svg
Lilly-Logo.svg
Endpoints & Readouts

What Sets Us Apart in Metabolic Biomarker Analysis

Our clients get more than data. They get clarity, confidence, and a partner built for the unique demands of drug development.

medal

35+ Years exclusively in stable isotope tracer studies

FILE-CHECK
Experimental protocol designs and results delivered weeks faster than CROs
FLASK

GLP-compliant, CLIA-certified, 21 CFR Part 11 validated

message-lines

Consultative approach, with over 1,000+ studies guided from design to submission

total_body_water_404

Why Measure Total Body Water?

The total body water (TBW) technique is a powerful tool for monitoring how the body responds under different conditions.

Researchers use it to:

  • Understand drug effects on fluid balance — for example, changes in fluid status after administration of Pioglitazone.
  • Track drug distribution in individuals with decreased total body water.
  • Assess body composition changes during illness, exercise, or dehydration.

By dividing TBW into compartments, alterations in body composition can also reveal the adequacy of nutritional support and the presence or progression of disease. 

How Stable Isotope Tracers
Measure Total Body Water

Stable isotopes of 18O and deuterium oxide (D₂O) have been used to measure total body water for more than 50 years. The principle is based on the fact that water is distributed in all parts of the body except body fat. 

deterium oxide

Deuterium oxide (D₂O): 

Most researchers choose D₂O because of its lower cost. The small (~4%) overestimation of TBW is corrected in the final calculations.

_oxygen 18 water

18O water: 

Frequently chosen when another deuterium-labeled tracer (such as 6,6-D₂-glucose) is co-administered in a study.

Together, these validated tracer methods provide reliable and reproducible measurements of total body water, supporting both research and clinical studies.

Tracer Protocols for Measuring Total Body Water and Extracellular Fluid

Total body water can be divided into intracellular and extracellular compartments, which vary independently and reveal important changes linked to nutrition, growth, or disease.

Body Fluid Compartments Direct measurement of extracellular water using sodium bromide (NaBr) dilution space.

When sodium bromide is co-administered with 18O or deuterium-labeled water, the extracellular water space can also be determined. Variations in extracellular water often reflect poor nutrition, growth, or disease, even when total body water appears unchanged.

Example: 70 kg Male

Compartment % of Body Weight % Total Body Water Volume (liters)
ECF 27 4.5 19
Plasma 4.5 7.5 3.2
ISF 12 20 8.4
Dense CT water 4.5 7.5 3.2
Bone water 4.5 7.5 3.2
Transcellular 1.5 2.5 1
ICF 33 55 23
TBW 60% 100% 42

If you need protocol information on how to conduct total body water tracer studies, the following technical paper is available: Total Body Water Determination.

All Analyses Are Performed In Our Certified Laboratory Environment

clia-certified 2 gold-laboratory-practice-badge 21-CFR-Part-11-Compliance-Badge 1

Trusted by Leaders in Metabolic Research

From discovery to submission, we’ve earned the confidence of industry innovators through precision, speed, and scientific depth.

They’ve been very consistent… the sample analysis and data has always been timely and high quality.

dan tardiff profile pic
Dan Tardiff CAMP4

There are academic labs that do it as well, but they’re much harder to engage and contract with.

scott turner
Scott Turner Arda Therapeutics

I think they’re extremely organized and very on top of sample management. All the interactions that I’ve had with them have been great.

1517416694305-removebg-preview (1)
Morganne A. Ultragenyx
Looking for Answers?

Frequently Asked Questions

Which tracers are used to measure total body water?

We use deuterium oxide (D₂O) and 18O. D₂O is most often chosen because of its lower cost, while 18O is preferred when another deuterium-labeled tracer (such as 6,6-D₂-glucose) is co-administered.

Why is the total body water technique useful?

It is used to monitor fluid status after drug administration, drug distribution in individuals with decreased total body water, and changes in body composition during illness, exercise, or dehydration.

How is extracellular water measured?

Metabolic Solutions offers direct measurement of extracellular water using sodium bromide (NaBr) dilution space. This approach is safe, inexpensive, accurate, and compatible with 18O or D₂O total body water techniques.

Contact Us

Measure Total Body Water Safely and Accurately

Leverage decades of stable isotope experience and our validated NaBr tracer method to expand your body composition research.
contact-background-image-femal-lab-flasks-flipped

Metabolic Solutions, LLC.
460 Amherst St., Nashua,
NH 03063, USA

Hours of Operation
Monday – Friday
7:30 am – 6:00 pm EST 

Contact us

Metabolic Solutions, LLC.
460 Amherst St., Nashua, NH 03063, USA

(603) 598-6960

(603) 598-6973

Breath Tests: support@metsol.com

Research: info@metsol.com

Hours of Operation
Monday – Friday
7:30 am – 6:00 pm EST

Research Services

GI Breath Tests

About Metabolic Solutions

©2025 Metabolic Solutions, LLC. All Rights Reserved. | Privacy Policy