Interfering substances, like proteins, are usually present in blood specimens for testing. These substances, if not eliminated, would be a contributory factor to the inaccuracy of laboratory results because they may increase or decrease the readings of other substances tested in blood.
When protein content of blood is not the test, then, the preparation of a protein free filtrate (PFF) will eliminate proteins from the specimen.
A protein free filtrate is free from these interfering substances giving out accurate results. This would greatly aid the Clinician in the proper diagnosis of the patient.
A few of these tests include creatinine, blood urea nitrogen, and uric acid. Creatinine and urea nitrogen are tests for kidney function, muscular diseases and other metabolic conditions. Uric acid is a test for the condition called gout, which may cause gouty arthritis, tophi, and nephrolithiasis.
There are several methods of preparing a protein free filtrate (PFF). Here is a simple and short method for this procedure.
TRICHLOROACETIC ACID PFF
1. Extract 5 ml of blood and obtain the serum or plasma.
2. In a 50 ml Erlenmeyer flask, pipette 4.5 ml of 5 % TCA reagent.
3. Add 0.5 ml of serum or plasma.
4. Cover and mix vigorously by rotating the flask, until precipitates form.
5. Filter or centrifuge for 5-10 minutes at 2,000 t0 2,500 revolutions per minute (rpm).
6. The supernatant fluid should be clear and colorless. This would indicate that you have performed the procedure properly.
7. Separate the clear, colorless supernatant fluid from the sediments into a clean and sterile test tube by using a Pasteur pipette.
8. Discard the sediments into proper containers.
9. Label the specimen vessels properly.
10. Cover the test tube containing the PFF, with parafilm and save the specimen in the refrigerator at 2-8 degrees centigrade for future testing procedures.
