Acidic PH of pleural fluid

Q: All of the following pathologies will cause pleural fluid acidosis EXCEPT? - select one

A) Malignancy

B) Tuberculosis

C) Urinothorax 

D) Misplaced central line

E) urease-splitting organisms 

Answer: E

Pleural effusion analysis remains an integral part of the differential diagnosis in most of the pulmonary pathologies with pleural effusion. Identifying the pH of pleural fluid is a valuable way to narrow down the cause of the underlying disease. Pleural fluid acidosis, particularly if combined with low glucose, is a given complicated parapneumonic pleural effusion or empyema, proven otherwise, EXCEPT for urease-splitting organisms such as Proteus species, which usually cause a spuriously elevated pleural PH.

The other causes of acidic pleural effusion are all the other choices in the question, i.e., malignancy, tuberculosis, urinothorax, misplaced central venous catheter infusing isotonic saline, along with rheumatoid pleuritis and lupus pleuritis.

Putting pleural fluid analysis in context with the history and other findings almost always led clinicians to the right diagnosis.

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References:

1. Pine JR, Hollman JL. Elevated pleural fluid pH in Proteus mirabilis empyema. Chest 1983; 84:109.

2. Sahn SA. State of the art. The pleura. Am Rev Respir Dis 1988; 138:184.

3. Houston MC. Pleural fluid pH: diagnostic, therapeutic, and prognostic value. Am J Surg. 1987 Sep;154(3):333-7. doi: 10.1016/0002-9610(89)90623-5. PMID: 3307471.

4. Bowmaster SM, Merrill AE, Manning NL, Wilson JS, Gross TJ. Improving Pleural Fluid pH Accuracy: A Quality Improvement Initiative. J Appl Lab Med. 2025 Nov 4;10(6):1593-1599. doi: 10.1093/jalm/jfaf118. PMID: 40891251.