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pH, PLEURAL FLUID
Test CodepH, PLEURAL FLUID
Preferred Specimen
Specimens must be drawn anaerobically in a syringe. Remove needle prior to submitting the lab. All other specimen containers are unacceptable.
Minimum Volume
150 uL
Transport Temperature
Room temperature
Specimen Stability
Specimens must be run STAT within 1 hour of collection
Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Specimens exposed to air
Methodology
The pH are based on the principle of ion-selective electrodes in which electrical potential can be established across a membrane resulting from chemical selectivity of the membrane to a specific ion. The potential can be described by this simplified form of the Nernst equation E=E’ +(S x Log C), where E is the electrode potential, E’ is the standard potential for that membrane, S is the sensitivity (slope), and C is the ion activity. E’ and S can be determined by the sensor response to the Process Control Solutions, and the equation can be solved for the activity of the ion of interest. For pH, “log C” is replaced by “pH” and the equation solved accordingly. The pH and electrolyte sensors are polyvinyl chloride (PVC) based ion selective electrodes, consisting of an internal Ag/AgCl reference electrode and an internal electrolyte layer. Their potentials are measured against the card reference electrode (Ag/ Ag+). The cross-section view in the figure below shows the flow of the solution past an ion-selective sensor.
FDA Status
Fluid PH test was developed and its performance characteristics determined by VA BHS Laboratory. It has not been cleared or approved by the FDA. The laboratory is regulated under CLIA as qualified to perform high-complexity testing. This test is used for clinical purposes. It should not be regarded as investigational or for research.
Setup Schedule
24/7
Limitations
Reference Range
>/= 7.30
Clinical Significance
Pleural Fluid pH measurement has the highest diagnostic accuracy in assessing the prognosis of parapneumonic effusions. A parapneumonic exudate with a pH greater than7.30 will generally resolve completely with medical therapy alone. A pH les than 7.20 indicates a complicated parapneumonic effusion, requiring surgical drainage. Patients with borderline complicated exudates between 7.20-7.30 may be closely watched, with repeat measurements.
A pH value below 6.0 is characteristic of esophageal rupture.
Ascetic Fluids- pH may be helpful in the diagnosis of SBP in patients with cirrhotic ascites, especially if it used in conjunction with leukocyte counts. A pH of less than 7.32 has a reported sensitivity and specificity of about 90% for SBP. Patients with ascetic fluid pH of less than 7.15 have a poor prognosis. Low pH is also found in patients with malignant and pancreatic ascites and tuberculosis peritonitis.
A pH value below 6.0 is characteristic of esophageal rupture.
Ascetic Fluids- pH may be helpful in the diagnosis of SBP in patients with cirrhotic ascites, especially if it used in conjunction with leukocyte counts. A pH of less than 7.32 has a reported sensitivity and specificity of about 90% for SBP. Patients with ascetic fluid pH of less than 7.15 have a poor prognosis. Low pH is also found in patients with malignant and pancreatic ascites and tuberculosis peritonitis.
Performing Laboratory
West Roxbury Chemistry
Jonathan Dryjowicz-Burek
857-203-5418
Last Updated: February 4, 2026
