Expert Insight: Pleural fluid analysis: Clinical implications of pleural fluid pH measurement and the importance of testing with a blood gas analyzer

Watch this on-demand webinar with Dr. Cheryl Frydman to discover the importance of measuring pH in pleural fluid when making diagnostic decisions

03 Nov 2021

Dr. Cheryl Frydman
Cheryl Frydman, M.D., Director of Clinical Laboratories and Associate Director of Pathology, White Plains Hospital

In this SelectScience webinar, now available on demand, Cheryl Frydman, M.D., Director of Clinical Laboratories and Associate Director of Pathology, White Plains Hospital, discusses various clinical conditions where the measurement of pH, as well as other analytes, in pleural fluid is critical to diagnostic decisions. The issues and challenges of pleural fluid sampling and analysis is also discussed, taking into consideration the methodologies available and selection of those optimum for accurate testing.

Watch this webinar to learn about the importance of pleural fluid pH testing in the diagnosis and treatment of patients with pleural effusions, as well as to:

  • Understand the testing options available for pleural fluid analysis.
  • Recognize the value of pleural fluid measurements in the diagnosis of pleural effusions.
  • Identify the potential hurdles to overcome when implementing pleural fluid analysis.

Read on for the live Q&A session or register to watch the webinar at a time that suits you. 

Q: Can other body fluids besides pleural fluid be tested for pH on a blood gas analyzer?

CF: Currently, only pleural fluid can be tested on a blood gas analyzer for pH, other than whole blood. That's the only other fluid that has been FDA approved for blood gas analyzer testing for pH. Other body fluids can't be tested on a blood gas analyzer or should not be tested on a blood gas analyzer. If that were to occur, this would be considered a laboratory-developed test, which would be a clear high-complexity test, with all the regulatory requirements surrounding this type of situation. Generally, we test other types of body fluids using pH meters in the main laboratory.

Q: Can pleural fluids be tested for other analytes besides pH on a blood gas analyzer?

CF: It would be convenient to be able to also test pleural fluid for glucose on blood gas analyzers. However, that is not an FDA-approved analyte right now. As we discussed, glucose is a very helpful measurement in determining patient management, in addition to the pleural fluid pH measurements. The literature examining any type of point-of-care pleural fluid glucose testing is very, very limited. But as we can see, this would be valuable when pleural fluid pH testing or accurate pleural fluid pH testing on a blood gas analyzer is not available.

Q: As blood gas analyzers are used in a point-of-care setting, is pleural fluid testing considered a CLIA-waived test?

CF: There is a misnomer that if an analyzer or any tested methodology is done in a point-of-care setting, such as in a doctor's office, that these are all CLIA-waived tests, but that is not the case. And generally speaking, all these test systems must be investigated as to whether they are CLIA-waived or moderate complexity. In the case of blood gas analyzers, these are not CLIA-waived analyzers or tests, and they are considered moderate complexity, with everything that goes along with a moderate complexity type of a test.

Q: How many different testing methodologies are available?

CF: A lot of clinicians are not aware of the different testing methodologies that are available for pleural fluid pH testing. But it's generally accepted in the clinical world right now that pleural fluid pH should and must be tested on a blood gas analyzer in order to have the most accurate and precise measurements. If you're using a different methodology, please be aware that this is not the preferred method and that your measurements may be higher than they are in reality.

Q: How are patients with borderline complicated exudates, with a pH greater than 7.2 but less than 7.3, managed?

CF: Patients with borderline complicated effusions, meaning effusions that have pleural fluid pHs between 7.2 and 7.3, can be quite challenging to manage. The clinical recommendation is that they can be closely watched with repeat measurements if fluid is available. However, also a concomitant pleural fluid glucose level is strongly recommended. And if the pleural fluid glucose levels are less than 60 milligrams per deciliter, this strongly suggests an impending empyema, and most likely, drainage is necessary.

Q: Could you tell us a little bit about how pleural fluid is collected, and how long it's stable for, and the effect of oxygen?

CF: Pleural fluid should not be directly collected into a cup. Pleural fluid should be collected in a heparinized blood gas syringe. If testing in a cup is necessary, such as a sterile cup for microbiology purposes, that can be a separate collection, or pleural fluid could be transferred from a syringe into a cup. The stability for pH testing has been looked into mainly in blood gas syringes. There's quite a bit of literature on the stability of pleural fluid pH collection. But generally, it will stay stable for about an hour, even at room temperature. And ice is not necessary if it's going to be collected and tested right away, as it should be, for immediate clinical decision making.

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