Dysphagia Knowledge Hub — 吞嚥困難知識庫

IDDSI Levels 0, 1, and 2 — The Thin to Mildly Thick Liquid Spectrum

Most published guides to the International Dysphagia Diet Standardisation Initiative (IDDSI) framework focus on the food textures — Levels 3 through 7 — because those are what families modify for three meals a day. But the liquid levels at the bottom of the IDDSI pyramid — Level 0 (Thin), Level 1 (Slightly Thick), and Level 2 (Mildly Thick) — are just as important, and arguably more dangerous when prescribed incorrectly. Thin liquids that flow too fast can cause aspiration into the lungs within a fraction of a second; slightly thick liquids that are not thick enough can fail to protect a patient with silent aspiration; and mildly thick liquids that are over-thickened can reduce fluid intake to dangerous levels and trigger dehydration.

This guide explains the three liquid levels in precise clinical terms, how to prepare each one correctly, how to verify compliance with the IDDSI 10-second flow test, the evidence for when each level is appropriate, and the practical hydration challenges that caregivers face.

The IDDSI Liquid Pyramid

The IDDSI framework describes eight levels (0-7), where Levels 0-4 are liquids or semi-liquids and Levels 3-7 are foods. Levels 3 and 4 overlap because “Liquidised” food (Level 3) is simultaneously a “Moderately Thick” liquid, and “Pureed” food (Level 4) is simultaneously an “Extremely Thick” liquid.

Level Name Flow Test Result Typical Use Case
0 Thin Flows completely through 10 mL syringe in under 10 seconds (more than 8 mL flows) Regular diet; no dysphagia
1 Slightly Thick 4-8 mL remains in syringe after 10 seconds Pediatric dysphagia, infant formula
2 Mildly Thick 4-8 mL + can be sipped from a cup Mild adult dysphagia
3 Moderately Thick Cannot be sipped from a cup — must be drunk from a spoon or cup with care Moderate dysphagia, early post-stroke
4 Extremely Thick Holds shape on a spoon Severe dysphagia

The distinction between Levels 0, 1, 2, and 3 is made with a standardised test using a standard 10 mL slip-tip syringe filled to the 10 mL line, then releasing the plunger for exactly 10 seconds.

Level 0 — Thin Liquid

Level 0 is any drink you could normally pour into a cup and sip without thought: water, tea, coffee, milk, juice, broth, beer, soup, cola. The technical definition in IDDSI is that in the 10-second flow test, more than 8 mL of the 10 mL initial volume flows out of the syringe.

When Level 0 is Prescribed

Level 0 is the normal liquid level for anyone without dysphagia. For dysphagic patients, Level 0 is prescribed when:

The Frazier Free Water Protocol

Developed at the Frazier Rehabilitation Institute in Kentucky in 1984, this protocol allows patients with known aspiration risk to drink plain water (and nothing else — no juice, no coffee) between meals, even while remaining on thickened liquids during meals. The rationale is that:

A 2019 systematic review in Dysphagia found that the Frazier protocol does not increase pneumonia rates compared to strict thickened-liquid regimens, while substantially improving hydration and patient satisfaction. It is now adopted by many rehab hospitals in the US, UK, Australia, and Hong Kong (though not universally).

Level 1 — Slightly Thick

Level 1 is a rare level in adult dysphagia care — it is primarily used in pediatric dysphagia, especially for infants who need a slightly thicker formula to manage reflux or mild swallowing delay. In adult care, Level 1 is sometimes used as a transition level during rehabilitation.

Visual description: Level 1 looks like standard infant formula. It pours smoothly from a bottle, can be drunk from a cup, and drips off a spoon in rapid drops. It is thicker than whole milk but thinner than buttermilk.

Flow test result: 4-8 mL remains in the syringe after 10 seconds.

Why Level 1 is Rare in Adults

For adult dysphagic patients, there is usually no clinical advantage to Level 1 over Level 0 (if the patient can manage thin liquids) or Level 2 (if they cannot). The flow characteristics of Level 1 are too close to Level 0 to meaningfully reduce aspiration risk, yet it adds the cost and complexity of thickeners. Adult SLPs almost always prescribe either Level 0 or Level 2, skipping Level 1.

Level 1 in Pediatric Practice

In infants with gastroesophageal reflux disease (GERD) or bottle-feeding dysphagia, Level 1 (slightly thicker formula) is a common first intervention. Commercial products like Enfamil AR and similar are pre-thickened to approximately Level 1. Parents should never manually thicken infant formula with cereal unless specifically directed by a pediatrician, as too-thick formula in an infant’s bottle nipple can cause air swallowing and nipple collapse.

Level 2 — Mildly Thick

This is the first level that is commonly used in adult dysphagia care. Level 2 is the most frequently prescribed liquid modification for:

Visual description: Level 2 is about the consistency of nectar or a smooth fruit purée juice. It can be drunk from a cup but flows noticeably slower than water. If you tilt the cup, it streams slowly rather than gushing.

Flow test result: 4-8 mL remains in the syringe after 10 seconds. (Note that this is the same syringe test result as Level 1 — the distinction is made additionally by the “drinkable from a cup” criterion, which applies to Level 2 but not Level 1.)

When Level 2 is Clinically Indicated

Speech-language pathologists typically prescribe Level 2 when:

Level 2 is NOT Indicated When:

Preparing Levels 1 and 2 — The Thickener Science

To make Level 1 or Level 2 from a thin liquid, you add a thickening agent. There are three main categories:

1. Starch-Based Thickeners

The original dysphagia thickeners (1990s-2000s), such as Thick & Easy and ThickenUp Original, are based on modified maize starch. They are cheap and effective but have significant drawbacks:

These are now considered second-line thickeners and are recommended only if the alternatives are unavailable or contraindicated.

2. Gum-Based Thickeners (Xanthan Gum)

Modern thickeners like Nestlé ThickenUp Clear, Fresubin Clear, and SimplyThick use xanthan gum as the main thickening agent.

Advantages:

Disadvantages:

3. Gel-Based Thickeners

Less common, based on carrageenan or agar. Used mainly for preparing pre-formed “gelled” drinks (popular in Japan) where a Level 3 or Level 4 “drink” can be served as a soft jelly.

Thickener Dosing for Level 2 (Mildly Thick)

Exact dosing depends on the brand, but typical ratios are:

Thickener For 200 mL of water For 200 mL of juice For 200 mL of milk
Nestlé ThickenUp Clear 1.2 g (1 scoop) 1.2 g 1.2-1.5 g
Fresubin Clear 1.2 g 1.2 g 1.5 g
Thick & Easy (starch) 3 g (1.5 scoops) 3 g 4 g
SimplyThick 1 pouch (6 g) 1 pouch 1 pouch

Always verify with the IDDSI flow test after preparation — thickener absorbency varies with temperature, liquid acidity, and age of the product.

The IDDSI Flow Test Step-by-Step

Every caregiver and staff member preparing thickened liquids should learn this test. It takes 30 seconds:

  1. Use a 10 mL slip-tip disposable syringe (not Luer-lock). These are available at pharmacies for HKD 2-5 each.
  2. Remove the plunger completely.
  3. Place your finger firmly over the tip opening.
  4. Fill the syringe to the 10 mL mark.
  5. Release your finger and simultaneously start a 10-second timer.
  6. At exactly 10 seconds, cover the tip again to stop flow.
  7. Read the remaining volume in the syringe:
    • >8 mL (i.e., <2 mL flowed out) = Level 3 Moderately Thick or thicker — too thick
    • 4-8 mL remaining = Level 1 or Level 2 (depending on other criteria)
    • 1-4 mL remaining = between Level 1 and Level 0 — undefined, not allowed
    • <1 mL remaining (>9 mL flowed out) = Level 0 Thin — not thick enough for Level 1/2

This test must be done at room temperature with the thickened liquid at rest for at least 1 minute after mixing.

Palatability and Hydration Challenges

The single biggest clinical problem with Levels 1 and 2 is inadequate fluid intake. Studies consistently show that patients on thickened liquids drink 30-40% less total volume than the same patients on thin liquids, even when both groups are offered the same total amount. The reasons are:

  1. Taste and texture are unfamiliar. Water with thickener tastes “wrong” to someone who has drunk plain water their entire life.
  2. Thickened coffee and tea lose their “refreshing” quality. Hot beverages especially feel disappointing when thickened.
  3. The sensation of satiety arrives faster — thicker fluids trigger satiety signals more quickly, leading to earlier cessation of drinking.
  4. Fear of choking — patients who have had one or more choking episodes become anxious about drinking and limit their intake.

The clinical consequences are serious: dehydration in elderly patients causes delirium, constipation, urinary tract infections, acute kidney injury, and increased mortality. A 2020 Australian study found that dysphagic patients in long-term care had a 22% incidence of clinically significant dehydration within 6 months of starting thickened liquids — more than 3× the rate in non-dysphagic peers.

Strategies to Improve Hydration on Levels 1 and 2

  1. Offer fluids on a schedule, not only when the patient asks. A cup of Level 2 liquid every 2 hours while awake should be the minimum.
  2. Use Frazier Free Water Protocol for between-meal water if clinically appropriate.
  3. Flavour the Level 2 drinks — use Ribena, lemon cordial, or ginger syrup to improve palatability.
  4. Serve at the right temperature — cold Level 2 drinks are significantly more palatable than room-temperature ones; the cold also provides extra sensory stimulation to the oral cavity, which can actually improve swallowing safety.
  5. Offer ice chips — these are technically “eaten” not “drunk” and can be a useful supplement for patients who tolerate cold.
  6. Pre-thickened commercial drinks — companies like Nestlé (ThickenUp Juice) and Fresubin sell pre-thickened Level 2 juices in tetra-paks. These are more expensive but eliminate preparation errors and improve compliance because they taste more like “real” drinks.
  7. Track daily intake on a chart — caregivers should record each cup of fluid consumed. Target is usually 1500-2000 mL/day for adults.

Common Errors in Thickened Liquid Preparation

  1. Using the wrong measuring spoon. Thickener scoops vary in volume (4 g, 6 g, 9 g). Using the wrong spoon can double or halve the thickener amount.

  2. Mixing into hot liquids incorrectly. For gum-based thickeners, the powder must be added slowly while stirring vigorously — dumping it in all at once creates lumps that never dissolve. Starch thickeners work differently: they should be added to cool liquid first and then heated.

  3. Not waiting for full thickening. Xanthan gum takes 60-90 seconds to reach its final viscosity. Serving immediately gives a misleadingly thin result; the drink then continues thickening in the patient’s mouth, which can cause choking.

  4. Re-thickening an already-thickened drink. If a caregiver feels a prepared drink “looks too thin” and adds more thickener, the result is typically Level 3 or Level 4 rather than Level 2. Always perform the flow test first and re-prepare from scratch if the first attempt failed.

  5. Thickening carbonated drinks. Soda water, tonic water, and sparkling wine do not thicken properly with standard thickeners — the bubbles interfere with the gum network. Use only still liquids.

  6. Thickening alcoholic drinks. Wine, spirits, and beer can be thickened but the alcohol content slightly alters thickener behavior. Test carefully before serving.

Equipment for Preparing Level 2 at Home

A home caregiver managing a dysphagic patient on Level 2 liquids needs:

Level 2 and Medication Administration

Patients on Level 2 liquids cannot take pills with water — they must take pills with a Level 2 thickened liquid to prevent aspiration. This affects:

Always ask the pharmacist for the liquid formulation of any medication prescribed to a dysphagic patient. See the separate guide on medication administration for dysphagia.

Level 2 vs Level 3 — When to Upgrade

Some patients gradually lose their ability to manage Level 2 and need to be stepped up to Level 3 (Moderately Thick). Warning signs include:

When these signs appear, notify the SLP within 24 hours for reassessment. Do not self-upgrade to Level 3 without clinical review — doing so may further reduce fluid intake and trigger dehydration.

Global Variations in Dysphagia Liquid Guidelines

Before IDDSI was adopted, different countries used different terms:

Since 2019, IDDSI has been adopted as the global standard, and all these older terminologies are being phased out. A nutrition label saying “Thick & Easy Nectar Consistency” corresponds to approximately IDDSI Level 2, while “Honey Consistency” corresponds to Level 3. Any patient transferring between facilities or countries should bring a printed IDDSI level specification from their SLP.

Resources

Summary

The three bottom levels of the IDDSI framework — 0, 1, and 2 — cover the spectrum from regular thin liquids to the mildly thickened nectar consistency that is the most common first-line modification for adult dysphagic patients. Level 1 is rarely used outside pediatric practice; Level 2 is the workhorse of early adult dysphagia care. Correct preparation requires a calibrated thickener, the IDDSI 10-second flow test, and attention to palatability and hydration adequacy. The biggest danger is not aspiration (which the thickening is designed to prevent) but dehydration from reduced fluid intake — which, in elderly dysphagic patients, is a more common cause of hospital readmission than aspiration pneumonia. Approach Level 2 with the same seriousness as any medication dose: the correct level, at the correct dose, at the correct frequency, monitored for effectiveness.