Effect of the choice of WHO International Reference Preparation for thromboplastin on International Normalised Ratios.

Abstract

Testing was to be performed on five separate days on fresh plasma samples from four normal subjects and 12 patients stabilised for at least six weeks with oral anticoagulants. INR were to be between 1 5 and 4 5. The exercise was to be completed within four hours of blood being collected. A single exercise was designed as follows: the specimens were collected, by clean venepuncture, into a 1 in 10 volume of sterile trisodium citrate 0I109 to 0 120 mol/l, into a plastic or polypropylene syringe, and transferred into a non-wettable container. If an evacuated tube was used the brand selected had to be sufficiently siliconised. First 1-2 hours: collection and preparation of test samples. The blood was centrifuged immediately after withdrawal and the plasma transferred to a non-wettable, stoppered container. Specimens were maintained at room temperature until required for testing. Second 2 hours: testing of the 16 fresh plasma samples with the three thromboplastins was done according to a randomised sequence provided.Single determinations were requested and the three prothrombin times on each plasma (one with each thromboplastin) were performed immediately after each other.The order in which the patients were to be tested was the same as the order of collection.

Effect of thromboplastin and coagulometer interaction on the precision of the International Normalised Ratio.

“…Furthermore, some potential sources of imprecision are unique to the INR system. Besides thromboplastin/instrument interaction, variables such as the choice of the primary reference preparation for calibration'6 or 16 the selection of mean "normal" plasma mater-ial17 create notable variability.…”

“…(T Clin Pathol 1995;48: [13][14][15][16][17] Keywords: Prothrombin time, anticoagulants, quality control.…”

More on: Is there a need for replacement of the international reference preparation for thromboplastin, bovine, combined (OBT/79)?

“…Published reports have described INR differences on the same anticoagulated patientsÕ blood samples using current IRP [6,7]. In one study four centers each performed full WHO fresh plasma ISI calibrations using the human (BCT/253) and rabbit IRP (RBT/90) [6].…”

“…The palindromic arrangement of int22h-2 and int22h-3 may favor their intra-chromosomal gene conversion and thus help explain why these sequences are fivefold more identical when they are on the same chromosome [6].…”

Capillary testing in an anticoagulant clinic: comparison of two methods

“…The Instrumentation Laboratory reagent is calibrated using a rabbit brain international reference reagent; the Manchester Capillary reagent is calibrated using the human brain international reference reagent BCT 441. Discrepancy between international reference preparations has been documented5 and is being rectified as they are replaced.…”