I’ll let you in on a little secret. For years, I’ve hated thickening liquids, and I’ve hated teaching others how to do it. Why? Because it felt like guesswork to me. Turns out that I wasn’t wrong, and I’m not alone!
But that’s all changed with IDDSI’s gravity flow test. Now we have an easy, reliable way to tell if liquids are the correct thickness.
Free DIRECT download: Thickening liquids: IDDSI flow test (cheat sheet & patient handout). (Email subscribers get free access to all the resources in the Free Subscription Library.)
Outline:
- Why do we thicken liquids?
- Can’t we just err on the side of caution and thicken more?
- What are the problems with the old method?
- IDDSI? What is that?
- What is the gravity flow test?
- How do we use the flow test to ensure the correct thickness?
- Where can I find the correct syringe?
- Do I have to do the test every time?
- How do I find more resources?
- Related Eat, Speak, & Think posts.
- A challenge to you.
Why do we thicken liquids?
Thickening liquids is one strategy to reduce the risk of aspiration pneumonia. Aspiration pneumonia is a serious condition that may result in hospitalization or death.
We know that aspiration isn’t sufficient to cause aspiration pneumonia. After all, up to 30% of healthy adults demonstrate trace aspiration of thin liquids, and the findings were consistent a year later in a subset of healthy older adults.
But healthy adults are unlikely to develop an aspiration pneumonia. Why exactly is that?
It’s because of what John Ashford, Ph.D. calls the “3 pillars of aspiration pneumonia.” In addition to aspirating, a person also has to have a weakened immune system and poor oral care. You can listen to Dr. Ashford talk about it on the Swallow Your Pride podcast.
So, if we see on an instrumental swallow test that someone is aspirating thin liquids, we may recommend thicker liquids as a safer alternative. (Recommendations depend on a number of factors, including aspiration pneumonia risk level, effectiveness of any swallow maneuvers, what actually is happening in the oropharynx when that person is swallowing thicker liquids, and our patient’s wishes.)
We do have evidence to suggest that thickening liquids reduces aspiration, which you can read about in “The Influence of Food Texture and Liquid Consistency Modification on Swallowing Physiology and Function: A Systematic Review“, published by Catriona Steele, Ph.D., and colleagues in 2015.
Can’t we just err on the side of caution and thicken more?
I often run across the belief among healthcare providers that thickening liquids is a benign intervention. Meaning, if someone is coughing on thin liquids, the doctor, nurse, or private home health aide will just go ahead and thicken them. They seem to assume that if someone is not coughing, then they aren’t aspirating.
The truth is that thickening liquids is not a safe intervention, particularly without an instrumental assessment. One reason is due to the phenomenon of “silent aspiration“, which is when a person does not cough or give outward sign when they aspirate.
Steele and colleagues’ systematic review mentioned above also found evidence in the literature that thicker liquids are associated with more residue left in the throat after swallowing. This residue could then be aspirated.
Robbins et al (2008) suggested that people who drink honey thick liquids are at higher risk for aspiration pneumonia. And of the people who are hospitalized with an aspiration pneumonia, those drinking honey thick liquids were hospitalized longer than those drinking nectar thick or using a chin tuck with thin liquids. (Although called honey thick, this was actually pudding thick.)
Liquids have to be properly mixed to be effective. My observation is that many people don’t measure, don’t mix properly, and don’t allow the liquid to thicken. Just stirring in thickener doesn’t magically make the drink safe!
Even when liquids are thickened correctly, the person is at risk of aspirating them. For instance, a person may aspirate thickened liquids if they aren’t sitting upright, if they drink faster than recommended, or if they talk before swallowing completely.
So we thicken liquids to reduce the likelihood of aspiration, but only after a thorough assessment and discussion with the patient and/or their family. And it’s important that people drink the recommended level of thickness, not too thick and not too thin.
What are the problems with the old method?
Our old system of thickening liquids, under The National Dysphagia Diet (2002), has a number of problems:
- Arbitrary cut-offs between thin, nectar, honey, and pudding-thick liquids.
- Thickness levels based on centipose, which we can’t measure in the field.
- Variation between manufacturers.
- Manufacturers’ target was to have the right thickness at room temperature. But temperature affects thickness (and most of our liquids are taken cold or hot).
- Confusion about which is thicker, “nectar” or “honey” thick.
- SLPs couldn’t accurately sort out 10 samples into different thicknesses.
- And SLPs couldn’t reliably mix the right thickness.
- Hospital staff couldn’t reliably mix the right thickness.
I strongly recommend listening to John Holahan’s interview on the Swallow Your Pride podcast (episode 73). John Holahan is the co-founder of Simply Thick, and he’s a strong supporter of IDDSI. Listening to the interview, you’ll learn about how Simply Thick got started, the problems with our “nectar thick”, “honey thick”, and “pudding thick” system, how IDDSI got started, and about the flow test.
Among the many things I learned from John Holahan* was that the NDD was never meant to be the final word on thickening liquids. The NDD was intended as a starting point and was always meant to be superseded by something with more evidence behind it.
And now we have IDDSI.
*I also completed a continuing education seminar on IDDSI given by John Holahan, sponsored by a subscription group, The Medical SLP Collective.
IDDSI? What is that?
IDDSI stands for the International Dysphagia Diet Standardisation Initiative. This group of volunteers from around the world is headed by Peter Lam, a dietician in Canada, and Julie Cichero, Ph.D., an SLP from Australia.
The board also includes a doctor, an ENT, a nurse, a food scientist, an engineer, a dietician, an occupational therapist, and three more SLPs. IDDSI is supported by corporate sponsors, such as Simply Thick. Corporate sponsors don’t have any say in IDDSI’s decisions but recognize the benefits of international standardization and the benefit to their customers.
IDDSI has designed an evidence-based standard of terminology to describe and categorize all foods and liquids into levels. And the best part is, they’ve found easy ways that anyone working in any setting (or families at home) can tell if they’re providing the recommended diet.
IDDSI is being adopted in the US by ASHA and the ADA on May 1, 2019. It’s voluntary now, but will almost certainly become mandatory in the future.
What is the gravity flow test?
The gravity flow test is an easy way to reliably measure the thickness of liquids. You simply need a certain type of syringe and a 10-second timer. To give you an idea, this video shows a side-by-side comparison of the test with drinks of 3 different thicknesses:
IDDSI didn’t invent the gravity flow test. For instance, it’s used in the construction industry to test for leaks and in the food industry for predicting the mouthfeel of liquids.
In the dairy industry, the Posthumus funnel is the tool that’s used to measure the thickness of dairy products. The slip-tip syringe used in the IDDSI flow test is based on the same principles
The IDDSI flow test is based on extensive testing to ensure that it’s a reliable and easy test that anyone can do to determine how thick a liquid is.
How do we use the flow test to ensure the correct thickness?
1. Thicken the liquid, following the manufacturer’s instructions
It’s important to follow the instructions for the specific thickener you’re using. Otherwise, you may end up with the wrong thickness and/or with lumps. I’ve included directions for two types of thickener for comparison.
John Holahan reported that you can use any utensil to mix their new formulation, EasyMix Simply Thick. Add a packet to four ounces of liquid and stir for 20 seconds. There’s no waiting period.
With Hormel’s Thick & Easy Clear, start with a clean, dry cup. Add the measured powder to the cup. Then add four ounces liquid quickly while stirring with a fork until the powder is dissolved. The liquid takes time to thicken, ranging from two minutes for water to nine minutes for honey-thick juice.
Of course, you may also test the thickness of any natural beverage such as whole milk or a yogurt drink. Just be sure there are no lumps or particles that may clog the syringe!
2. Perform the gravity flow test three times
With IDDSI, the push is to ensure that beverages are the correct thickness when they are served and consumed. So test the beverage at the temperature(s) it will be consumed at.
The gravity flow test is an easy way to reliably measure the thickness of liquids. You’ll need two 10ml syringes and a 10-second timer. One syringe is the test syringe, and the other is used to fill the test syringe to avoid bubbles. You can watch a short video here:
- Remove the plunger from one syringe and plug the nozzle with your finger.
- Fill it with 10 mL of fluid, using another syringe to avoid bubbles.
- Remove your finger for 10 seconds, allowing the fluid to drain out naturally.
- Place your finger over the nozzle to stop the flow after 10 seconds.
- Read how much is left.
IDDSI’s rule is to run the liquid through the syringe three times to ensure accurate measurement.
Avoid bubbles and lumps as they will affect the test results.
3. Compare the results to IDDSI’s chart
Each time you perform the gravity flow test, compare the fluid remaining in the syringe with IDDSI’s chart.
- Level 0: Thin liquid (less than 1 mL left).
- Level 1: Slightly thick (1 – 4 mL left). This is mainly used in pediatrics.
- Level 2: Mildly thick (4 – 8 mL left). Similar to nectar thick.
- Level 3: Moderately thick (no less than 8 mL left). Similar to honey thick. Confirm with Fork Drip test.
- Level 4: Extremely thick. (too thick for syringe). Confirm with Fork Drip Test AND Spoon Tilt Test.
NOTE: If you run the test three times and your result is exactly 4 mL or 8 mL, then you have to adjust your recipe.
For instance, let’s say that you’re goal is a mildly thick liquid, and your test result is 4 mL exactly. That is right on the line between slightly thick and mildly thick and is considered to be neither. You’d have to add more thickener and re-test. (See “IDDSI Testing – Drinks: Exactly 8 or 4 mL? on the FAQ page.)
If it’s too thick, add more liquid. If it’s too thin, add more thickener.
4. Additional tests for moderately thick and extremely thick liquids
The IDDSI Framework Testing Methods download describes the Fork Drip Test on page six and the Spoon Tilt Test on page seven.
The Fork Drip Test for Level 3 and Level 4
Use the Fork Drip Test to test Level 3 moderately thick (~honey thick) and Level 4 extremely thick (~pudding thick).
Use a fork to scoop up some liquid and hold it above the cup. Watch to see how the liquid flows off the fork.
A Level 3 moderately thick liquid will “drip slowly or in dollops/strands through the tines of the fork.”
A Level 4 extremely thick liquid will “sit in a mound or pile above the fork. A small amount may flow through and form a tail below the fork.”
The Spoon Tilt Test for Level 4
Use the Spoon Tilt Test for Level 4 extremely thick (~honey thick) to test how sticky and cohesive the liquid is.
Scoop up some liquid onto the spoon. It should hold its shape.
Then tilt the spoon and give a little flick onto a plate. The liquid should slide off easily and shouldn’t stick to the spoon. The liquid should hold its shape or spread just a little when it hits the plate.
5. Clean your syringes and re-use
You can re-use the syringes until the lines become difficult to read. IDDSI suggests pumping warm soapy water through the syringe three times, followed by clean warm water twice.
Where can I find the correct syringe?
You can’t use just any 10mL syringe to perform the test. It has to be the right size and shape for the test to be accurate.
Currently, IDDSI advises using a BD 10ml slip tip (Leur tip) syringe which is reference number 303134 (or, if you’re in Australia, BD REF 302143). The length of the scale printed on the syringe must be 61.5 mm. (See this update in the April 2019 IDDSI e-bite newsletter.)
You can confirm that your syringe is the right type with the water calibration test. Fill the syringe to 10ml with water and time how long it takes to run out. The syringe should empty in seven seconds. (Described on slide 14 of this IDDSI presentation).
Your facility or company may have these syringes in stock or may be able to order them. Alternatively your local pharmacy may be able to give you some. Check with your area representative for thickeners to see if they have any they could send. Or you may even have luck checking with your mobile dysphagia testing companies.
Do I have to do the test every time?
No! This is science, which means if you follow the same mixing procedure, then the results will be the same.
Once you test a specific beverage at drinking temperature, you can be sure how thick it is each time you mix it in the future (as long as you follow the same procedure).
If anything changes, then do the gravity flow test again. For instance, test again if you change the brand of beverage or thickener. Or test again if your patient had been drinking their coffee black and now wants to add cream.
Where do I find more resources?
The best place to go is IDDSI.org, which offers a wealth of information, resources, and tools to help us implement the new framework. For instance, on the “Resources” page, you’ll find:
- Posters.
- Handouts.
- Implementation materials.
- Presentations.
- Publications.
- E-bites monthly newsletter archive.
- News releases.
- Videos.
- Webinar recordings.
- Resources from other IDDSI users.
- Country-specific resources.
IDDSI offers a free app in iTunes and Google Play, which includes the framework, training videos, handouts, description of levels, posters, webinar recordings, FAQ, and more. Simply search for “IDDSI” and download. You’ll have to set up an account and log in.
Check out IDDSI’s YouTube channel, which has more than 30 videos.
Another great source may be thickener manufacturers. For instance, SimplyThick sent me a supply of the IDDSI Flow Test Cards, as well as plastic cups with ounces marked for mixing. You can also order the Flow Test cards yourself by following the directions on IDDSI’s Implementation page.
Related Eat, Speak, & Think posts
- 10 factors that increase risk of aspiration pneumonia.
- A practical guide to pureed food at home.
- ALS guide for SLPs.
- 9 free swallow assessment tools.
- Single-use swallow evaluation folders.
A challenge to you
If you’re not already using the gravity flow test, give it a try. Find a couple of syringes and try the test out at home. I’m so happy that IDDSI has taken the guesswork out of thickening liquids. I like having a reliable method for measuring the thickness of liquids. It’s a big step forward for our field!
Free DIRECT download: Thickening liquids: IDDSI flow test (cheat sheet & patient handout). (Email subscribers get free access to all the resources in the Free Subscription Library.)
Featured image by Nathan Dumlao on Unsplash.
Lisa earned her M.A. in Speech-Language Pathology from the University of Maryland, College Park and her M.A. in Linguistics from the University of California, San Diego.
She participated in research studies with the National Institute on Deafness and other Communication Disorders (NIDCD) and the University of Maryland in the areas of aphasia, Parkinson’s Disease, epilepsy, and fluency disorders.
Lisa has been working as a medical speech-language pathologist since 2008. She has a strong passion for evidence-based assessment and therapy, having earned five ASHA Awards for Professional Participation in Continuing Education.
She launched EatSpeakThink.com in June 2018 to help other clinicians be more successful working in home health, as well as to provide strategies and resources to people living with problems eating, speaking, or thinking.
[…] Take the guesswork out of thickening liquids with the IDDSI flow test. […]
how can i get a smooth drink without slimy lumps at the bottom of the drink please
Hi Christine,
Thanks for your question! I bet that’s a common problem people have. I don’t know what kind of thickener you’re using or how you’re mixing it, but you should be able to prepare thickened liquids without slimy lumps at the bottom of the cup. You may have to use a different thickener, however.
For example, if you use Simply Thick gel, you simply add the thickener to a specific amount of liquid and stir briskly for 30 seconds. I’ve never seen slimy lumps with this gel thickener.
Hope that helps!