plasma

The fluid portion of the blood that, after centrifugation, contains all the stable components except the cells. It is obtained from centrifuged whole blood that has been prevented from clotting by the addition of anticoagulants such as citrate, oxalate, or heparin.

The fluid portion of the blood in which corpuscles are suspended. Plasma is to be distinguished from serum, which is plasma from which the fibrinogen has been separated in the process of clotting.

• p. bound — many electrolytes exist in plasma in a form in which they are bound to protein which reduces their lability and liability to loss in the urine, e.g. protein-bound iodine.
• p. cell gingitivitis–pharyngitis — see feline plasma cell gingivitis–pharyngitis.
• p. cell myeloma — see multiple myeloma.
• p. cell pododermatitis — a nonpainful swelling with ulceration and exuberant granulation tissue on the footpads of cats. The cause is unknown but believed to be immunological.

  Plasma cell pododermatitis in a cat.

• p. clearing factor — a lipoprotein lipase which lipolyses the triglyceride in the chylomicrons of the plasma and hence clears it of cloudiness.
• p. exchange — the removal of plasma from withdrawn blood (plasmapheresis) and retransfusion of the formed elements and type-specific fresh-frozen plasma into the donor; done for removal of circulating antibodies or abnormal plasma components.
• p. expanders — see plasma volume expander.
• fresh-frozen p. — prepared from whole blood; a source of coagulation factors.
• p. protein — the heterologous group of proteins in circulating blood that includes albumin, lipoproteins, glycoproteins, transcortin, haptoglobin, ceruloplasmin, cholinesterase, α₂-macroglobulin, erythropoietin, transferrin, hemopexin, fibrinogen, plasminogen and the immunoglobulins (γ-globulins).
• p. protein:fibrinogen (PP:F) ratio — an indicator of significant changes in fibrinogen levels, taking into account dehydration.
• p. substitute — a fluid suitable for use as a replacement for plasma in the animal body. Usually a solution of gelatin or dextran.
• therapeutic p. concentration — a therapy–response relationship determined only by experiment; the plasma level which is matched by the desired therapeutic response.
• p. thromboplastin antecedent — clotting factor XI; see plasma thromboplastin antecedent.
• p. turbidity test — a qualitative test for fat absorption, performed by comparing the turbidity of plasma before and 2, 3 and 4 hours after the oral administration of fats, usually vegetable oil. Results are greatly influenced by delays in gastric emptying, so normally this test can only be relied upon to rule out malabsorption or maldigestion when evidence of absorption is found.
• p. volume — the estimation of plasma volume is essential to a complete knowledge of a patient's fluid status. The common technique is by the intravenous injection of a known amount of a dye such as Evans blue and the subsequent measurement of the dilution that it has undergone in a set time period.