Research Tuesday: “Clinical Utility of the 3-Ounce Water Swallow Test”

Once again, it’s time for research Tuesday! And once again, I’m pondering dysphagia. First, to give a little credit where credit is due, I wanted to disclose that my inspiration for this post came from Jonathan Waller over at Dysphagia Cafe. His past couple posts (see here and here) have had me seriously reconsidering my (albeit very early and still-developing) understanding of aspiration, particularly the silent variety. He points out that silent aspiration may not actually be so silent after all, and that it is widely misunderstood and overly feared by clinicians. So, in an effort to not be misunderstanding and fearful, I delved into this article.


Article: Suiter, D, & Leder, S. (2008). Clinical utility of the 3-ounce water swallow testAmerican Journal of Speech-Language Pathology, 14, 61-70.

Background: The 3-ounce water swallow test is used frequently, but before this study, limited research was available. A larger, broader study needed to be performed to determine if it was a good predictor of aspiration and if it could be used to make dysphagia recommendations.

Purpose: “To investigate the clinical utility of the 3-ounce water swallow test for determining aspiration status and oral feeding recommendations in a large and heterogeneous patient population.”

What They Did: Data was collected from 3000 patients over a seven year period. These patients participated in a fiberoptic endoscopic evaluation of swallow (FEES) to determine if aspiration (silent or not) occurred. Immediately after this, the 3-ounce water test was administered, and it was documented whether the patient passed or failed. (Failure = inability to drink full amount, coughing or choking up to 1 min after completion, or presence of post-swallow wet-hoarse vocal quality.) The authors then measured true positives (aspiration on FEES, then failed water swallow test), true negatives (no aspiration on FEES, then passed water swallow test), false positives (no aspiration on FEES, but still failed water swallow test) and false negatives (aspiration on FEES, but still passed water swallow test).

Results:

The article breaks down some of these scores more specifically based on diagnosis. These are just the overall results.

Does the 3-ounce water swallow test identify individuals who aspirate thin liquids? 

1. YES, the 3-ounce water swallow test DOES identify individuals who aspirate thin liquids pretty darn consistently. (96.5% of the time.) In other words, it has good sensitivity, or “true positive.”

2. HOWEVER, it was less accurate at predicting when patients AREN’T actually aspirating. In other words, it had so-so (48.7%) specificity, or “true negative.” So there was a 51.3% false positive rate. Meaning more than half the time, patients wouldn’t aspirate on the FEES, but would still fail the 3 ounce water swallow test.

Does a failed 3-ounce water swallow test identify individuals who are also unsafe for oral alimentation based on results of an instru- mental swallow assessment? 

1. 70.6% of participate who failed the 3-ounce water swallow test were still able to tolerate some sort of PO diet per the FEES results.

2. Sensitivity (true positive) was again quite good (96.4%).

3. Specificity (true negative) was again so-so, at 46.4%. So there was a 54.6% false positive rate.

Does a successfully passed 3-ounce water swallow test permit specific diet recommendations to be made without further objective swallow assessment?

Per FEES results, of those who passed the 3-ounce test…

1. 56% were cleared for a regular diet.

2. 13% were cleared for a soft diet.

3. 4% were cleared for a chopped diet

4. 25% were cleared for a puree diet.

5. 0.3% were cleared for a liquid diet.

6. 1.5% were made NPO. (False negatives.)

Real Life Applications: Wow, that is a lot to take in! Here’s my takeaway…

1. Yay, the 3-ounce water swallow test is EXCELLENT for predicting aspiration, EVEN THE SILENT KIND! Seriously, what a relief this is. This means that when I do my bedside, I have a pretty reliable measure to show me that aspiration isn’t occurring. I don’t have to fret so much over “but what if they are silent aspirating?”

2. If fact, IF the water swallow test is passed, patients can have an oral diet without further diagnostic dysphagia testing. This is good news not only for us, but also for RNs who complete the 3-ounce water swallow test and then wonder if they can recommend solid consistencies based on this. The article just says we should recommend puree for edentulous patients and soft/regular for dentate patients. Not too shabby.

3. But hold your horses, just because someone fails the 3-ounce doesn’t mean they should be placed NPO for the rest of their lives. First of all, there are a lot of false positives. So just because we see “aspiration” during the 3-ounce doesn’t mean that the person is truly aspirating. And even if they are, there is a decent chance they will be safe for some sort of PO diet, even if it is modified.

4. It would be hard to make specific diet recommendations based solely on failure of the 3-ounce. In the words of the authors, “Failure on the 3-ounce water swallow test did not accurately reflect true oral feeding status.”

5. One of the biggest concerns I had after reading this was about patients who do well on smaller amounts but fail the 3 ounce. While this could be an immediate indicator they are silent aspirating the smaller amounts, it could mean very little. This study shows I can’t make diet recommendations from the 3 ounce alone. So, is an objective study always the next step? Do I take in other individual factors and make my best recommendation? Based on the discussions I’ve seen about this on Facebook, it appears that SLPs do not have a cohesive opinion about this.

6. So is the 3-ounce water swallow test a good screening tool? Well, the answer of course, as with all dysphagia research, appears to be “eh, yes and no.” ;) It’s great at showing aspiration in people who are truly aspirating, but it will give a lot of unnecessary referrals for people who appear to be aspirating but are not actually doing so.

7. And of course, with all this talk of aspiration, let’s remember that it is not the end-all-be-all of whether or not an SLP should be consulted. For example, even if a patient does not fail the 3-ounce, they may benefit from SLP evaluation to determine appropriate recommendations for, say, impulsivity or fatigue.

Suggested Further Research: 

Enough dysphagia research already! My mind is still processing what’s out there.  (Kidding, of course.)

1. When discussing this over lunch with one of my colleagues (hi Jessica!), she mentioned how she wished she could apply this research to thickened liquids. For example, say someone fails the 3-ounce water swallow test with thin liquids. Could this test reliably be used with nectar- or honey-thickened liquids?

Your Thoughts: Do you use the 3-ounce water swallow test? How much do you let it guide your clinical decision making?

One thought on “Research Tuesday: “Clinical Utility of the 3-Ounce Water Swallow Test”

  1. Pingback: Blogging about Research – August Edition | "Talks Just Fine"

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