Dysphagia Knowledge Hub — 吞嚥困難知識庫
IDDSI Flow Test: Liquid Thickness Measurement
Overview
The IDDSI Flow Test is the standardised method for classifying the thickness of liquids across IDDSI Levels 0 to 4. It uses an inexpensive, universally available 10 mL syringe as the measuring device. The test was developed because traditional viscosity measurement (using viscometers) is inaccessible to most care settings; the syringe provides a practical proxy that correlates with clinical texture categories.
The test is applicable to water, juice, milk, tea, coffee, soup, nutritional supplements, and thickened drinks — any pourable liquid that a dysphagia patient might consume.
Equipment
- 10 mL syringe (standard, without needle — Luer slip tip preferred; barrel ID ~15.9 mm, tip ID ~1.1 mm)
- Timer or watch with seconds
- Sample of liquid to be tested (~15 mL)
- Cup or bowl
Note: The IDDSI website provides specifications for the exact syringe type. Off-brand syringes with different barrel diameters will give different results. Use a consistent syringe type across your facility.
Method
Step 1: Hold a finger over the tip of the syringe (closed position). Draw up exactly 10 mL of the liquid into the syringe.
Step 2: Hold the syringe vertically, tip pointing down, over a cup or bowl. Remove your finger from the tip to start the free flow.
Step 3: Start timing immediately. Allow the liquid to flow freely for exactly 10 seconds.
Step 4: At exactly 10 seconds, block the syringe tip again with your finger. Read the residual volume remaining in the syringe barrel.
Interpreting Results
| Residual volume after 10 sec | IDDSI Level | Name |
|---|---|---|
| >8 mL remaining | 0 | Thin |
| 4–8 mL remaining | 1 | Slightly Thick |
| 1–4 mL remaining | 2 | Mildly Thick |
| 0–1 mL remaining | 3 | Moderately Thick |
| Nothing flows; ≥1 mL remains AND holds shape | 4 | Extremely Thick / Pureed |
Key rule: If no liquid flows at all and the residual is close to 10 mL, the liquid may actually be Level 4 (too thick to flow). Confirm with Spoon Tilt or Fork Drip Test.
Thickener Adjustment Guide
When a tested liquid does not meet the target IDDSI level:
Too thin (flows too freely):
- Add ¼ teaspoon of xanthan gum-based thickener per 200 mL, stir thoroughly, wait 2 minutes (thickener continues to hydrate), then retest.
- Starch-based thickeners react more slowly and may require up to 5 minutes for full thickening.
Too thick (residual <1 mL for target Level 1 or 2):
- Add a small volume of un-thickened liquid and stir, then retest.
- Document the final thickener dose per volume of liquid for kitchen consistency.
Clinical Applications
New thickener prescriptions: Before prescribing a thickener brand and dose, test the resulting liquid at the target IDDSI level in your facility’s water. Results vary by water temperature, mineral content, and brand.
Caregiver education: The Flow Test is easy to teach to caregivers at home using syringes from a pharmacy. Providing a visual reference chart (residual volume = IDDSI level) simplifies monitoring.
Kitchen audits: Randomly test drinks served to dysphagia patients weekly. Thickener clumping, incorrect measuring, and temperature variation are common causes of non-compliance.
Research consistency: The Flow Test provides a standardised outcome measure for comparison across dysphagia research studies.
Common Errors
- Wrong syringe size: Using a 20 mL or 5 mL syringe changes the bore diameter and invalidates the result.
- Tilted syringe: The syringe must be held strictly vertical. Angling reduces flow rate and overestimates thickness.
- Timing error: Starting timing before removing the finger, or stopping before 10 seconds, changes the result.
- Temperature not standardised: Test at room temperature (20°C) unless clinically required otherwise. Hot liquids are thinner; cold liquids are thicker.
References
- IDDSI Framework (2019). Testing Methods. https://iddsi.org/Testing-Methods
- Cichero JA, et al. (2017). Development of international terminology and definitions for texture-modified foods and thickened fluids used in dysphagia management. Dysphagia, 32(2):293–314. DOI: 10.1007/s00455-016-9758-y
- Steele CM, et al. (2015). The international dysphagia diet standardisation initiative framework. Dysphagia, 30(6):692–703. DOI: 10.1007/s00455-015-9634-8
- Garcia JM, et al. (2005). Thickened liquids: practice patterns of speech-language pathologists. Am J Speech Lang Pathol, 14(1):4–13. DOI: 10.1044/1058-0360(2005/003)