How to Test for Thickened Fluids in IDDSI

January 4, 2026 •

4 min read

Over one million people worldwide have swallowing difficulties (dysphagia), making standardised thickened fluids a critical safety measure. The International Dysphagia Diet Standardisation Initiative (IDDSI) provides a global framework and specific testing methods to ensure these fluids have the correct, consistent thickness.

Quick Summary

The IDDSI framework uses specific, evidence-based tests to accurately verify thickened fluid consistency, crucial for dysphagia management. Key methods include the 10mL Flow Test for liquids and the Fork Drip Test for thicker pureed levels. Correct testing ensures safety by preventing complications like aspiration and choking.

Key Points

Flow Test for Liquid Levels: The IDDSI Flow Test uses a 10 mL slip-tip syringe to measure how much liquid remains after 10 seconds, precisely categorizing Levels 0 through 3 based on the volume left.
Fork Drip Test for Thicker Fluids: The Fork Drip Test is crucial for verifying Levels 3 and 4, assessing whether a fluid or pureed item drips slowly (Level 3) or forms a cohesive mound (Level 4) on a standard fork.
Spoon Tilt Test for Cohesiveness: The Spoon Tilt Test is used for Levels 4 and 5 to check if a substance holds its shape on a spoon and slides off cohesively when tilted, indicating proper consistency and non-stickiness.
Test at Serving Temperature: Fluid consistency can change with temperature, so it is essential to perform IDDSI tests on samples at the intended serving temperature for accurate results.
Standardize Equipment for Consistency: Using consistent testing equipment, such as syringes with specified dimensions and standard forks, ensures reliable and comparable results across all users.
Test the Full Spectrum: A combination of IDDSI tests is often necessary to classify a product correctly. For example, Level 4 fluids require verification with both the Fork Drip and Spoon Tilt Tests.

Understanding the IDDSI Framework for Fluids

The International Dysphagia Diet Standardisation Initiative (IDDSI) framework offers a continuum of eight levels, from 0 to 7, to classify food texture and drink thickness. For liquids, the relevant levels range from 0 (thin) to 4 (extremely thick), with each level having a precise description and specific testing method. The core purpose of these tests is to provide an objective, repeatable way to check the fluid's viscosity, removing the subjectivity of descriptive terms like 'honey-thick' or 'nectar-like' that were previously used. The testing should always be performed on the fluid at the temperature it will be served, as consistency can change significantly with temperature.

The IDDSI Flow Test: The Standard for Liquids

The most important and foundational test for thickened fluids at Levels 0-3 is the IDDSI Flow Test, which uses a 10 mL Luer slip-tip syringe. This test measures how much fluid flows out of the syringe over a ten-second period, providing a precise, quantitative result. Consistency is key, so it is vital to use syringes with consistent barrel dimensions (61.5 mm length from the 0 to 10 mL mark) to ensure reliable results across different users and settings.

Step-by-step procedure for the IDDSI Flow Test:

Take a 10 mL Luer slip-tip syringe and remove the plunger.
Block the tip of the syringe with your finger and fill it exactly to the 10 mL line with the fluid to be tested.
Hold the syringe over a cup or container. Start a timer for 10 seconds and, simultaneously, remove your finger from the tip to allow the fluid to flow freely.
After exactly 10 seconds, cover the tip again with your finger to stop the flow.
Measure the amount of fluid left in the syringe using the markings on the barrel. The volume remaining indicates the IDDSI level.

Interpreting the Flow Test Results:

Level 0 (Thin): Less than 1 mL remains after 10 seconds.
Level 1 (Slightly Thick): 1-4 mL remains.
Level 2 (Mildly Thick): 4-8 mL remains.
Level 3 (Moderately Thick): More than 8 mL remains, but not all 10 mL.
Level 4 (Extremely Thick): All 10 mL of the fluid remains in the syringe.

The Fork Drip Test: For Thicker Consistencies

While the Flow Test covers most liquid levels, the Fork Drip Test is used for Levels 3 (Moderately Thick) and 4 (Extremely Thick) to assess a fluid or liquidized food's ability to hold together or drip slowly through the tines of a standard fork. This visual and tactile test complements the Flow Test, especially for substances that are too thick to flow through a syringe.

Procedure for the Fork Drip Test:

Load a sample of the thickened fluid or liquidized food onto the tines of a standard dinner fork.
Observe the fluid's behavior. For Level 3, the liquid should drip slowly in dollops through the prongs.
For Level 4, the fluid should sit in a mound or pile on the fork and should not drip continuously through the tines. A small amount may form a 'tail' below the fork.

The Spoon Tilt Test: Assessing Cohesiveness and Stickiness

For extremely thick fluids and purées (Levels 4 and 5), the Spoon Tilt Test is also critical for assessing cohesiveness and stickiness. This test ensures the food forms a cohesive bolus that falls off the spoon easily, rather than sticking or separating.

Procedure for the Spoon Tilt Test:

Scoop a spoonful of the extremely thick fluid or purée.
Tilt the spoon sideways. For Level 4, the fluid should hold its shape and fall off the spoon in a cohesive lump with minimal residue left on the spoon.
A gentle flick of the wrist may be needed to dislodge the sample, but it should slide off easily.

Comparison of IDDSI Fluid Testing Methods


Feature	IDDSI Flow Test	Fork Drip Test	Spoon Tilt Test
Equipment	10 mL Luer slip-tip syringe, stopwatch	Standard dinner fork	Spoon
Levels Tested	0 (Thin) to 3 (Moderately Thick)	3 (Moderately Thick) to 4 (Extremely Thick)	4 (Extremely Thick) to 5 (Minced & Moist)
Purpose	Measures flow rate and quantifies viscosity	Checks how fluid flows/drips through tines	Assesses cohesiveness and stickiness
Key Outcome	mL of fluid remaining in syringe after 10 seconds	Appearance of drips or mounds on fork	How cohesively the sample falls from the spoon
Best For	All thickened liquids, from slightly to moderately thick	Moderately and extremely thick liquids, purees	Extremely thick liquids and purees

Best Practices for Consistent Testing

For the most accurate and reliable results when testing thickened fluids, adhere to these key best practices:

Test at Serving Temperature: Always test the fluid at the temperature it will be consumed, as heat and cold can alter viscosity.
Standardize Your Equipment: Ensure all caregivers and staff use the same type and size of syringe and fork to minimize variation.
Use the Right Test: Choose the appropriate test based on the target IDDSI level. The Flow Test is for lighter thicknesses, while the Fork Drip and Spoon Tilt are for thicker fluids and purees.
Monitor Over Time: Some thickened products can change consistency over time. Test a sample after it has sat for a while to ensure it remains at the correct level.

Conclusion

Accurately testing for thickened fluids using the IDDSI framework is a crucial component of safe dysphagia management. By standardizing the testing process with tools like the 10 mL Flow Test, the Fork Drip Test, and the Spoon Tilt Test, caregivers and healthcare providers can ensure that individuals with swallowing difficulties receive the precise fluid consistency prescribed for them. This objective, evidence-based approach minimizes the risk of aspiration and choking, thereby enhancing safety and quality of life. Consistent training and adherence to these simple, practical methods are essential for all involved in the preparation and serving of thickened fluids. For more information, the official IDDSI website provides comprehensive resources and guides.(https://www.iddsi.org/standards/testing-methods)

Frequently Asked Questions

The primary test for thickened fluids (Levels 0-3) in IDDSI is the Flow Test, which uses a 10 mL syringe to measure how much fluid remains after flowing for 10 seconds.

The IDDSI Flow Test requires a standard 10 mL Luer slip-tip syringe with specific barrel dimensions (61.5 mm length from 0 to 10 mL mark) and a stopwatch.

During the Fork Drip Test, a Level 4 fluid will sit in a mound or pile above the fork tines and will not drip continuously. A small 'tail' may form below the fork.

Stickiness and cohesiveness are checked using the Spoon Tilt Test. A spoonful of the substance should slide off easily when tilted or gently flicked, with minimal residue remaining on the spoon.

Testing fluids at their serving temperature is important because heat and cold can significantly change the fluid's viscosity, which could affect its safety for a person with dysphagia.

No, it is crucial to use a 10 mL Luer slip-tip syringe with the correct barrel dimensions (61.5 mm length from 0 to 10 mL mark) to ensure accurate and reliable results.

If a sample falls between two IDDSI levels, it should be classified at the lower, thinner level, as this is the safer and more conservative approach for managing dysphagia.