A normal aPTT does not guarantee adequate coagulation factor levels.
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Blood Coagulation Factors↗
Biomedical subjects
M Oropeza
Publications and source records attributed to M Oropeza.
Performance characteristics of a new synthetic APTT reagent.
Performance characteristics of a totally synthetic activated partial thromboplastin time (APTT) reagent, recently available commercially, were evaluated and compared with a rabbit-brain extracted reagent. We found that the synthetic reagent, Synthasil, returned significantly higher normal APTT values than the brain-extracted reagent, Thrombosil. APTT ratios (APTT patients/normal mean APTT), yielded by Synthasil were higher in the majority of patients receiving heparin therapy. Synthasil also returned longer APTT values than did Thrombosil on normal plasma spiked with heparin. On patients with lupus anticoagulants, APTTs assayed with Synthasil were generally longer than with Thrombosil. However, the differences disappeared when APTT values were converted to ratios. Factors XII-, XI-, IX- and VIII-deficient plasmas supplemented with normal plasma to yield activities of 2-50%, generally gave longer APTTs with Synthasil than with Thrombosil. However, this was not always the case on plasmas from haemophilias A and B patients. No reduction in Synthasil activity was noted after the reagent had been left at 24 degrees C for 28 days.
Coagulation Protein Disorders↗
Stability of plasma for add-on PT and APTT tests.
We conducted studies to determine at what time point an add-on prothrombin time (PT) or activated partial thromboplastin time (APTT) test can be honored on specimens that have been received in the laboratory hours earlier without yielding results with clinically significant differences from those if the test had been performed on the original unstored plasma. PT and APTT tests were performed on blood samples from 20 healthy subjects, 30 patients receiving warfarin, and 30 patients receiving heparin anticoagulation therapy. The tests were performed on plasma prepared initially after the samples were obtained. The same tests were assayed on plasma that had been left on spun-down blood cells at room temperature for 2, 4, and 8 hours. We found that the PT of the majority of plasma samples from healthy subjects and from patients receiving oral anticoagulant therapy tended to become shorter on storage. However, the difference in PT values was small and had no clinical significance. In most cases, the APTT values for the stored plasma from healthy subjects tended to increase with time. Except in one specimen in which the 8-hour add-on APTT was 1.2 seconds longer than the APTT result for the original sample, all others had APTT results less than 1.2 seconds longer than the original values. In patients receiving heparin, the differences in APTT values between the initial and add-on tests were larger than those observed for healthy subjects. However, those differences are not beyond what we would accept for duplicate checks for heparinized samples with high APTT values. Unlike samples from healthy subjects, there was no obvious trend of time-related prolongation of the APTT in heparinized plasma. These results led us to believe that within an 8-hour period and with plasma on spun-down cells at room temperature, add-on tests for PT and APTT could be performed with results similar to what would be obtained from testing unstored samples.
Anticoagulants↗
Modified APC-resistance test: variable ratios with respect to source of factor V-deficient plasma.
A single point mutation of the factor V (FV) gene, leading to the substitution Arg506Gln in the FV molecule (FV-Leiden) and hence resistance to its breakdown by activated protein C (APC), is the most prevalent risk factor for venous thrombosis in the Caucasians. A ratio determined by activated partial thromboplastin time (APTT) of test plasma in the presence or absence of exogenous APC (the APC ratio), is the method widely used to screen individuals with this risk factor for thrombosis. Because of functional defects of vitamin K-dependent clotting factors in patients on oral anticoagulant therapy, this method cannot be applied to those patients without modification. One modification is to mix test plasma (1:5 or 1:10) with FV-deficient plasma so that 80-90% of functioning vitamin K-dependent factors are supplied by the FV-deficient plasma. Even with 10-20% of FV in the mixture, APC-resistance still can be demonstrated. In this report, we present our results of the modified APC-sensitivity assay using FV-deficient plasma from different commercial sources. APC ratios determined by the original method in which test plasma is not mixed with FV-deficient plasma can be significantly different from those determined by the modified method in which test plasma is diluted 1:5 with FV-deficient plasma. This difference between methods was observed not only in normal individuals, but also in FV-Leiden positive individuals, and in patients on warfarin therapy. Further, APC ratios varied significantly depending on the commercial source of the FV-deficient plasma. The modified method is apparently suitable to identify APC-resistance in patients on warfarin therapy, as well as in individuals not receiving anticoagulant treatment. However, one must be aware that APC-resistance ratios obtained with the modified method are likely to be different from those established with the original method, and the source of FV-deficient plasma can be a factor influencing the ratios in the former cases.
Anticoagulants↗
Meaning of serum free-thyroxin values in nonthyroidal illnesses: seven methods compared.
Serum free thyroxin (FT4) was determined in 40 patients with various nonthyroidal illnesses. We studied seven methods: (1) a free thyroxin index calculated from total T4 and triiodothyronine resin uptake; (2) a free T4 index determined by enzyme inhibitor assays (Abbott's "Tetrazyme" and "Thyrozyme"); (3) a free T4 index calculated from total T4 and thyroxin-binding globulin; (4) free T4 by equilibrium dialysis; (5) Amersham's free T4 RIA; (6) Clinical Assays' one-step free T4 RIA; and (7) Clinical Assays' two-step free T4 RIA. Approximately half of the free T4 results were in the euthyroid range and the other half in the hypothyroid range by methods 1, 2, 5, and 6. Results for free T4 by methods 3 and 7 were similar to those by equilibrium dialysis (method 4), the percentages of patients with results in the euthyroid range being 68%, 65%, and 76%, respectively.
Dialysis↗