pH, Body Fluid

Test ID: 


CPT code:



•Body Fluid pH

Clinical Use:

Determine pH of body fluid. Low pH may be encountered in a pleural effusion with leakage of gastric secretions as a result of a perforated ulcer, ruptured esophagus, empyema, rheumatoid pleurisy, and tuberculosis.

Additional Information: 

pH of pleural fluid <6.0 may indicate rupture of esophagus.1 pH <7.3 relates to inflammatory states: in empyema and in loculated effusions pleural fluid pH is <7.2 to 7.3.1,2

The pH is <7.2 in rheumatoid pleural effusion, which is characterized by low glucose, high LD (LDH), and high rheumatoid factor titer. pH >7.3 is in general a feature of transudates. Low pH and low glucose together are found with loculated effusion or with empyema.3 Effusions related to lupus erythematosus generally have a pH >7.35.1

Effusions of tuberculosis usually have pH <7.3,1 usually with increased lymphocytes.

In bacterial peritonitis pH is decreased: cutoff <7.35 is useful, especially with PMNs >500/mm3. The mean pH of infected ascitic fluid is reported as 7.24. The arterial-ascitic fluid pH gradient >0.10 with >500 PMNs is described as virtually diagnostic of bacterial peritonitis.4

Reduction of pH and in some, but not all, series increments of PMN counts may be found also with peritoneal metastases.4,5 Low pleural fluid pH with negative cytologic examination may indicate lack of recognizable malignant cells in a sample of malignant effusion but may point to tuberculosis or rheumatoid effusion. Differences in survival exist between patients with low pH and normal pH in malignant pleural effusions, a significant inverse relationship.5

A transudative low pH (<7.30) pleural fluid in which the pleural fluid:serum creatinine ratio is >1 point toward urinothorax, a possibility to be considered in patients with obstructive uropathy.6.

Specimen Type:

Serous fluids (pleural, pericardial, ascitic) or synovial fluid

Requested Volume: 

5 mL

Minimum Volume: 

1 mL

Container Type: 

Sample should be collected anaerobically. A lithium heparin tube to prevent clotting should be used, especially if the syringe has not been rinsed with heparin. Keep on ice.


A syringe rinsed with 0.2 mL heparin, 1:1000 may be used; collect anaerobically. If the specimen is collected in a syringe, all air should be expelled and the needle sealed and capped.

Storage Instructions:

Keep specimen refrigerated.

Rejection Criteria:

Spinal fluid (CSF), urine, feces, or blood specimen received

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Mon – Sat: 7AM-11PM

Sun: 7AM-3PM

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