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Pleural fluid: protein
Overview
- Total protein varies with changes in vascular permeability, osmotic pressure and tissue injury or chemotaxis.
- Pleural fluid protein is elevated in inflammatory processes.
- Used in conjunction with other laboratory tests on pleural fluid to diagnose the type of pleural effusion Pleural: effusion.
Uses
Alone
- Differentiate low protein from high protein effusions, eg transudate versus inflammatory exudate.
In combination
- With other tests to evaluate pleural effusion Pleural: effusion
- Cell count Peritoneal fluid: differential cell count.
- Cytology Pleural fluid: cytology.
- Culture and sensitivity Pleural fluid: culture and sensitivity.
Sampling
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Tests
Methodologies
- Refractometry:
- A drop of fluid is placed on refractometer plate.
- Most refractometers are calibrated to give a reading for total protein in g/dl. Multiply result by 10 to convert to g/l.
- Refractometry measures the refractive index (RI) of the fluid.
- The RI changes proportionally to changes in protein concentration.
- Precipation and dye binding methods.
- Urinary protein re-agent strips for detection of grossly elevated total protein.
Availability
- Widely available at commercial laboratories.
- Refractometry can be performed in house.
Technique intrinsic limitations
- It is assumed that there are no significant changes in the concentration of other solutes such as glucose, urea, lipids, etc which could, if elevated, give a false high reading by refractromety.
- Pleural fluid must be clear for refractometry. For example, presence of hemoglobin can raise readings.
Result Data
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