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FAQ - Testing Methods

Q: What is the IDDSI Flow Test?
A: The IDDSI flow test is designed to test the ability of a liquid to flow in conditions related to swallowing a bolus. The thickness level of the liquid is defined by the amount of fluid remaining in the 10 ml syringe after 10 seconds.
The test is suitable for IDDSI Levels 0-3. Since Level 4 liquids do not flow the fork-drip and spoon-tilt tests are used to differentiate between a Level 3 (moderately thick/liquidized) and Level 4 (extremely thick/puree).

Q: Why does the IDDSI framework not give values of viscosity for textured modified products?
A: The IDDSI framework does not use viscosity values for identifying texture modified products for the following reasons:

  • It’s not scientifically correct: Viscosity is used to describe Newtonian liquids (e.g. water, oil) however almost all thick drinks have shear-thinning non-Newtonian behavior. Their “apparent viscosity” depends on how they are tested.

  • It’s not specific enough: Two different liquid types (e.g. gum- vs starch-thickened) with exactly the same measured viscosity at any given shear rate (e.g. 50 /s) will not have the same measured viscosity at any other different shear rate. Nor will they necessarily appear the same or behave the same way when swallowed. 

  • It is not practical: Specialised, expensive equipment is required (e.g. rheometer / viscometer with cone-plate attachment) which is not available in health and community care settings.

In comparison, the IDDSI Flow test is inexpensive, accessible and easy to perform requiring only a 10 ml syringe and timer.

Q: Is there any place at all for using a viscometer and linking it with the IDDSI levels?
A: A viscometer such as the Brookfield can be very useful for internal auditing and product development where you are varying concentrations for one product (or a limited range).  If you restrict yourself to varying concentrations of one thickener powder for one type of liquid then you could create a relationship between concentration and IDDSI-syringe value, but unfortunately it is not possible to map one value of viscosity directly onto the syringe test for all different types of liquids.  

Q: Is the IDDSI Flow Test accurate?
A: Yes, in tests performed by the research community and international medical products industries, the IDDSI flow test has been demonstrated to be accurate and reliable.
The IDDSI Flow Test is based on the Posthumus funnel concept which has been used for many decades in the dairy industry to audit the thickness of milk, cream, yoghurt & custard. The geometry of the syringe allows for both shear and elongation flow types which represent flow conditions within the oral cavity and pharynx.
Q: Can I perform the IDDSI flow test with any 10 ml syringe?
A: No. It is important that the barrel of the 10 ml syringe meets the correct dimension as barrel sizes and shapes of different 10 ml syringes can vary (even though the Luer-tip nozzle is ISO-standardised). The 0-10 ml measure on the syringe should be 61.5 mm in length.
Check to make sure that there are no defects or blockages in your syringe: 10 ml of plain water should drain completely through the syringe in 7 seconds.
If you are having difficulty sourcing the correct syringe, contact your medical supplies purchaser or local medical supplies outlet.

Q: Do I need to recommend both food and drinks need to be a Level 3 or Level 4 when my patient is requiring either food or drinks at this level?
A: IDDSI level 4 (Pureed Foods and Extremely Thick Drinks), IDDSI level 3 (Liquidised Foods and Moderately Thick Drinks) are presented on the IDDSI framework as connected because of their flow property and behaviour is similar. It does not mean that they need to be prescribed together. Clinicians need to assess the patient’s ability to manage foods and drinks independently.
For example:  your patient may require liquids thickened to Level 3 due to poor oral control but can manage minced and moist foods Level 5. In this case, they would be prescribed Level 5 Minced & Moist, Level 3 Moderately Thick.

Q. How do I find the right syringe to use for the IDDSI flow test?
We have outlined the importance of testing fluids using the correct sized 10 ml syringe – one with a barrel length of 61.5 mm. This is essential in order to be able to accurately test your drink. The best way to ensure this is to check the barrel length is 61.5 mm and that it is either Luer lock or slip tip.  When you confirm the correct syringe, we suggest you note the code number on the syringe package for future ordering.  Note that syringe codes can differ by country. Code Examples:

  • North America: BD 303134 – 10ml slip tip, BD 302995 – 10 ml luer lock tip
  • Australia BD 302143 – 10 ml slip tip
  • Singapore BD 302143

Q:  Can I test any liquid product with the IDDSI flow test?
A: Yes. The IDDSI Flow Test can be used to test any type of liquid product provided it does not contain any lumps, particles, seeds etc. This means naturally thick drinks such as 'yogurt drinks' as well as those thickened with a commercial thickener product can be tested using the IDDSI Flow Test.