Body fluid pH test
Quick answer: This test measures how acidic or alkaline a body fluid sample is, such as fluid from around the lungs. It helps doctors work out the cause of fluid build-up and whether an infection needs drainage.
- SampleFluid
- TakesUsually 15 to 30 minutes for the procedure
- Before the testThe fluid sample is collected by a doctor during a procedure.
How the test is done
- 1The doctor explains the procedure and cleans the skin
- 2Local anaesthetic is given to numb the area
- 3A needle is used to draw fluid, for example from around the lung
- 4The sample is sealed and tested quickly, as delay can change the pH
What your results can mean
Reading your report
Normal ranges differ between labs, so compare your result with the range printed on your report and discuss it with your doctor.
If the result is outside the usual range
A low pH in fluid from around the lungs can point to an infection that may need draining, and can also be seen with some cancers or inflammation. A pH closer to normal suggests the fluid is less likely to be infected.
Who usually has this test
People with fluid collected around the lungs or in another body space, where the cause needs to be found.
Risks and aftercare
The puncture site may be sore for a day or two, and your doctor will watch for rare problems such as bleeding or a collapsed lung.
Names and options
Also called: fluid pH, pleural fluid pH
Listed by the hospital as
- PH, FLUID
Questions about this test
Why is pleural fluid pH measured?
When fluid builds up around the lungs with pneumonia, a low pH suggests the fluid is infected and may need to be drained with a tube. It helps doctors decide on treatment.
Why must the fluid sample be tested quickly?
Exposure to air and delay can change the pH of the sample. Labs usually ask for it to be collected in a sealed syringe and tested promptly.
What other tests are done on the fluid?
Doctors usually also check protein, LDH, sugar, cell counts and sometimes tests for infection or cancer cells. Together these help find the cause of the fluid.
Related tests
Tamara Hospital & IVF Centre, Rajajinagar
34/3, 10th Cross Road, opp. Vardhaka Sardar Patel School, 1st N Block, 2nd Stage, Rajajinagar, Bengaluru 560010
The hospital is open 24 hours. Call before you come to check the timing for your scan or sample collection.
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This page explains each test in general terms so you know what to expect. It is not medical advice: your doctor decides which tests you need and what your results mean. Reference ranges differ between laboratories. Updated 4 November 2026.