The Precise Consistency of Liquid in the IDDSI Framework

October 19, 2025 •

3 min read

According to the International Dysphagia Diet Standardisation Initiative (IDDSI), a global framework used in over 128 countries, liquid consistency is categorized into five distinct levels, from Level 0 (Thin) to Level 4 (Extremely Thick). The correct consistency of liquid in the IDDSI framework is crucial for patient safety, helping to prevent life-threatening complications like aspiration pneumonia.

Quick Summary

The IDDSI framework provides a standardized continuum of five drink consistency levels, from Thin to Extremely Thick, to manage dysphagia. The appropriate thickness is determined by clinical assessment and is objectively measured using the IDDSI Flow Test with a 10 mL syringe. Accurate liquid consistency is essential for improving swallowing safety and patient quality of life.

Key Points

Five Distinct Levels: The IDDSI liquid framework categorizes liquids into five precise levels: 0 (Thin), 1 (Slightly Thick), 2 (Mildly Thick), 3 (Moderately Thick), and 4 (Extremely Thick).
Objective Measurement: The IDDSI Flow Test is a simple, standardized method using a 10mL syringe to objectively measure liquid consistency and confirm the correct level.
Preventing Aspiration: Matching the correct liquid consistency to an individual's swallowing ability is crucial for preventing aspiration, where food or liquid enters the airway.
Standardized Terminology: The framework provides a universal language for healthcare professionals and caregivers, reducing confusion associated with subjective descriptions.
Temperature Matters: Liquid viscosity can change with temperature, so testing should always be performed at the intended serving temperature to ensure accuracy.
Levels Are Measurable: The core of the IDDSI system for liquids lies in the measurable results of the Flow Test, indicating how much liquid remains in the syringe after 10 seconds.

Understanding the IDDSI Liquid Levels

The International Dysphagia Diet Standardisation Initiative (IDDSI) was developed to provide a universal language for describing modified food and drink textures. For liquids, the framework outlines a spectrum of five consistencies, ensuring that individuals with dysphagia receive a diet tailored to their specific swallowing abilities. Each level is clearly defined and associated with a specific color and number for easy identification and improved communication among caregivers and clinicians.

Level 0: Thin

This level includes liquids that flow like water. They can be consumed using any type of cup, teat, or straw, depending on the individual's skills. While seemingly simple, managing thin liquids can be challenging for those with poor oral control, as the fast flow rate increases the risk of aspiration.

Level 1: Slightly Thick

Level 1 liquids are thicker than water and flow slightly more slowly. They can typically still be consumed through a standard bore straw or from a cup, though they require a little more effort than thin liquids.

Level 2: Mildly Thick

Mildly Thick liquids are noticeably thicker than Slightly Thick fluids and pour more slowly. While still 'sippable' from a cup, they require effort to drink through a standard bore straw. This level is often recommended when thin liquids are unsafe due to poor oral control.

Level 3: Moderately Thick

These liquids have a consistency similar to honey or thick cream soup. They flow slowly and in dollops through a fork. Level 3 liquids are best consumed from a cup or with a spoon.

Level 4: Extremely Thick

Extremely Thick liquids are the thickest, are not pourable, and are often eaten with a spoon. They move very slowly under gravity and should not be firm or sticky. It is crucial that these liquids are tested accurately to prevent choking risks.

The Role of the IDDSI Flow Test

To ensure liquids meet the precise consistency requirements, the IDDSI Flow Test is used. This simple, reliable, and accessible test utilizes a standard 10mL syringe. It provides an objective, measurable standard for each liquid level, removing the subjectivity associated with verbal descriptions.

IDDSI Flow Test Procedure

Prepare: Remove the plunger from a 10mL syringe and cover the tip.
Fill: Pour 10mL of the liquid into the syringe.
Start: Release the tip and start a timer for 10 seconds.
Measure: After 10 seconds, cover the tip and measure the amount remaining.

Interpreting the Results

Thin (Level 0): Less than 1 mL remains.
Slightly Thick (Level 1): 1–4 mL remains.
Mildly Thick (Level 2): 4–8 mL remains.
Moderately Thick (Level 3): No less than 8 mL remains.
Extremely Thick (Level 4): No flow; 10mL remains.

Comparison of IDDSI Liquid Levels


Feature	Level 0: Thin	Level 1: Slightly Thick	Level 2: Mildly Thick	Level 3: Moderately Thick	Level 4: Extremely Thick
Flow Rate	Flows like water.	Thicker than water; flows through a standard straw.	Pours quickly from a spoon, slower than thin liquids.	Drips slowly in dollops through fork prongs.	Sits in a pile; does not drip continuously.
Drinking Method	Cup, straw, or nipple.	Cup or straw; requires slightly more effort.	Cup or wide bore straw; requires effort.	Best from a cup or spoon.	Eaten with a spoon.
Syringe Test (10mL in 10s)	Less than 1 mL remains.	1–4 mL remains.	4–8 mL remains.	8–10 mL remains.	No flow; 10mL remains.
Consistency Analogy	Water.	Some fruit nectars.	Some milkshakes or cream soups.	Honey or thin pudding.	Thick pudding.
Lumps	Smooth.	Smooth.	Smooth.	Smooth, no lumps or fibers.	Smooth, no lumps.

Ensuring Accuracy and Safety

Proper preparation and testing are vital for patient safety. Temperature is a significant factor, as many thickeners are affected by heat. Testing the liquid at the intended serving temperature is essential. Liquids with starch-based thickeners can thicken over time, requiring re-testing. The IDDSI Framework is a critical communication tool, standardizing terminology and reducing confusion. Regular training on IDDSI standards and testing methods is a best practice.

Conclusion

In summary, the consistency of liquid in the IDDSI framework is categorized into five precise levels, each defined by measurable standards using the IDDSI Flow Test. This objective approach minimizes the risk of aspiration and dehydration for individuals with dysphagia, improving safety and quality of life. Healthcare providers and caregivers can follow these guidelines for consistent and safe nutritional care. For more detailed information, consider visiting the official IDDSI website to access comprehensive resources and educational materials.

Frequently Asked Questions

The IDDSI Flow Test is a simple and objective method for measuring the consistency of a liquid. It involves filling a 10mL syringe with the liquid and measuring how much remains after 10 seconds of flow.

The correct liquid consistency is vital for individuals with dysphagia (swallowing difficulties) to prevent aspiration, a condition where liquid enters the lungs, which can lead to complications like pneumonia.

No, an individual's ability to manage food and drinks must be assessed independently. A person might require a moderately thick liquid but be able to manage solid foods with a different texture.

To make a liquid slightly thick, a thickening agent is added to a standard thin liquid according to the manufacturer's directions. The final consistency is verified using the IDDSI Flow Test, where 1-4mL should remain in the syringe.

Mildly Thick (Level 2) liquids are sippable but require more effort through a straw, with 4–8mL remaining in the syringe during the Flow Test. Moderately Thick (Level 3) liquids flow in dollops, are often best consumed with a spoon, and result in 8–10mL remaining in the syringe.

Yes, temperature can significantly affect liquid consistency, especially when thickeners are used. It is essential to test the liquid at the temperature it will be served to ensure it is at the correct IDDSI level.

Extremely Thick (Level 4) liquids have a pudding-like consistency and are not pourable. They are eaten with a spoon and hold their shape, such as very thick, thickened pureed soups or puddings.