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PubMed1980

The use of reference plasmas in the control of oral anticoagulant therapy.

Beginning in 1967, several committees have attempted to formulate a consensus opinion on how best to standardize the control of oral anticoagulant therapy. The three major proposals that evolved were: 1) to agree on a standard thromboplastin that would serve as a "reference thromboplastin", 2) to explore mathematical approaches for comparing the results obtained with various thromboplastins, and 3) the use of assayed plasmas that would serve as a common reference material for all thromboplastins. The advantages of reference plasmas as a common reference and their usefulness in the standardization of oral anticoagulant therapy are discussed.

Administration, Oral↗

PubMed1994

Hemostatic assessment of patients before tonsillectomy: a prospective study.

The purpose of this prospective study in patients undergoing tonsillectomy was to determine whether perioperative bleeding could be predicted by use of a standardized questionnaire concerning bleeding risk combined with measurement of the activated partial thromboplastin time and prothrombin time. Of the 96 patients enrolled in the study, none had a history of a severe bleeding disorder, but 6 (6%) had histories suggestive of a mild bleeding disorder. Further evaluation showed possible von Willebrand's disease in one of these patients. Of the 90 patients with negative questionnaires, 16% had prolongation of the activated partial thromboplastin time. One of these patients had possible von Willebrand's disease. However, none of the patients with positive questionnaires or a prolonged activated partial thromboplastin time bled after surgery. Bleeding that resulted in additional hospital use occurred in 2% of patients, and blood-tinged sputum was described by 4% after discharge; all of these patients had negative questionnaires and normal screening studies. The data provide further evidence that routine measurement of the activated partial thromboplastin time and prothrombin time in asymptomatic patients is not useful for predicting postoperative bleeding. In addition, histories suggestive of a mild bleeding disorder are also not accurate predictors of postoperative bleeding. Excessive bleeding associated with tonsillectomy is usually not a result of an identifiable coagulation disorder.

Adenoidectomy↗

PubMed2000

Coagulation tests and anti-phospholipid antibodies in patients positive for lupus anticoagulant.

We examined activated partial thromboplastin time, kaolin clotting time, mixing with normal plasma in kaolin clotting time, dilute Russell's viper venom time, dilute Russell's viper venom time at high lipid concentrations, anti-phospholipid antibodies, and anti-cardiolipin-beta2-glycoprotein I complex antibody in 135 patients with prolongation of activated partial thromboplastin time and diagnosed 86 patients positive for lupus anticoagulant. The sensitivity of activated partial thromboplastin time and dilute Russell's viper venom time/dilute Russell's viper venom time-high lipid concentrations ratio for lupus anticoagulant were markedly high, but the specificity of activated partial thromboplastin time for lupus anticoagulant was not markedly high. The specificity, but not the sensitivity, of kaolin clotting time-mixing with normal plasma in kaolin clotting time was markedly high. In summary, dilute Russell's viper venom time to dilute Russell's viper venom time-high lipid concentrations ratio gave high sensitivity as well as specificity, being the only assay to confirm this. Of the patients positive for lupus anticoagulant, 25% were positive for anti-phospholipid antibodies and 17% were positive for anti-cardiolipin-beta2-glycoprotein I complex antibody. Of the lupus anticoagulant-positive patients with thrombosis, 45% were positive for anti-phospholipid antibodies, 35% were positive for anti-cardiolipin-beta2-glycoprotein I complex antibody, 60% were positive for both anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody, and only 17% were negative for anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody. These findings suggest that lupus anticoagulant can be diagnosed by dilute Russell's viper venom time/dilute Russell's viper venom time-high lipid concentrations ratio, and that thrombosis in lupus anticoagulant-positive may be predictable from both anti-phospholipid antibodies and anti-cardiolipin-beta2-glycoprotein I complex antibody. Plasma tissue type plasminogen activator level in lupus anticoagulant patients was significantly increased, and plasma tissue type plasminogen activator and fibrin-D-dimer levels in lupus anticoagulant-positive patients with thrombosis were significantly higher than in those without thrombosis, suggesting that the diagnosis of thrombosis by hemostatic markers might be important in lupus anticoagulant.

Adult↗

PubMed2005

Evaluation of diagnostic tests and argatroban or lepirudin therapy in patients with suspected heparin-induced thrombocytopenia.

STUDY OBJECTIVES: To evaluate diagnostic tests for heparin-induced thrombocytopenia (HIT), a serious drug reaction that can occur in patients receiving heparin, and to evaluate treatment with direct thrombin inhibitors-the only initial drug therapy that decreases the risk of thromboembolism associated with immune-mediated HIT. DESIGN: Retrospective cohort study. SETTING: University teaching hospital. SUBJECTS: Patients with HIT treated with argatroban or lepirudin between January 1, 2000, and December 31, 2003. MEASUREMENTS AND MAIN RESULTS: Patients were assessed for dosage and duration of argatroban or lepirudin therapy, HIT diagnostic tests, and clinically significant adverse events. Thirty-four patients received argatroban, 42 received lepirudin. Mean+/-SD doses of argatroban and lepirudin were 1.2+/-0.9 microg/kg/minute and 0.09+/-0.11 mg/kg/hour, respectively; both were 40% lower than the recommended doses. Mean duration of therapy was 10+/-9 days. Supratherapeutic activated partial thromboplastin times were observed in 30 (39%), 10 (13%) , and six (8%) of 76 patients on days 1, 2, and 3, respectively (p<0.0001). Clinically significant bleeding occurred in 6% of patients receiving argatroban and in 5% of those receiving lepirudin (p=0.99); all patients had an activated partial thromboplastin time of longer than 100 seconds. Although platelet-aggregation tests were ordered in 55 (72%) of 76 patients, they were not useful in 16 (29%) because of equivocal or contradictory results. CONCLUSION: Due to supratherapeutic activated partial thromboplastin times, our patients often required doses of argatroban and lepirudin lower than those usually recommended. Thus, direct thrombin inhibitors should be started at low initial doses and titrated to target activated partial thromboplastin times to achieve appropriate efficacy and to avoid increasing the risk of bleeding. Platelet-aggregation tests were least useful for evaluating HIT. Appropriate diagnostic strategies should be used to avoid unnecessary drug use.

Anticoagulants↗

PubMed1978

Control of oral anticoagulants by the prothrombin time: a plea for uniformity.

Six trromboplastins commonly used for prothrombin time determinations were studied. Prothrombin times of patients who were receiving oral anticoagulant therapy varied widely, depending on the origin of the thromboplastins. The therapeutic range which is recommended with one thromboplastin is often quite different from that recommended with another, and as a result, the therapeutic ranges of different institutions may show no overlap. Management of patients and comparison of therapeutic results would be facilitated if all thromboplastins in use in Australia were standardized by comparison with the Australian Reference Thromboplastin.

Administration, Oral↗

PubMed1992

Some characteristics of blood shed into the Solcotrans postoperative orthopaedic drainage/reinfusion system.

OBJECTIVE: To assess the suitability of blood shed into the Solcotrans orthopaedic autotransfusion system as a source of autologous blood for transfusion. DESIGN: Blood samples were taken from patients after surgery and from shed blood within the Solcotrans units. SETTING: Surgery was performed at a public hospital. PATIENTS: All six patients underwent total knee replacements. MAIN OUTCOME MEASURES: Measurements were made of haemoglobin, haematocrit, platelets, pH, potassium, plasma haemoglobin, fibrinogen, D-dimer, plasminogen activator, thromboplastin and fibrinopeptide A. The non-activated partial thromboplastin time was estimated. Shed blood was compared with homologous whole blood to assess the thrombogenic potential of shed blood in vitro. RESULTS: The haemoglobin and haematocrit levels of the shed blood were significantly lower than venous blood (P = 0.008). Levels of potassium in shed blood were normal although there was significant haemolysis. Shed blood was depleted of clotting factors, with increased levels of D-dimer (16-128 g/L). Activation of the coagulation pathway within the shed blood was shown by a shortened non-activated partial thromboplastin time (90-120 s), and detectable levels of thromboplastin. Propionibacterium acnes was isolated from one of the units. CONCLUSION: Reinfusion of large volumes of shed blood should probably be avoided, but use of the Solcotrans orthopaedic transfusion system in conjunction with other autologous transfusion practices can reduce the patient's requirement for homologous blood.

Blood Coagulation Tests↗

PubMed2006

Effect of fondaparinux on coagulation assays: results of College of American Pathologists proficiency testing.

CONTEXT: Fondaparinux, a factor Xa inhibitor, is approved for thromboprophylaxis after orthopedic surgery and for treatment of venous thromboembolism. It may also be efficacious, safe, and cost-effective for other patients; thus, more widespread use of fondaparinux is likely. The effect of fondaparinux on coagulation testing needs to be thoroughly examined. OBJECTIVE: To report the effects of fondaparinux on coagulation tests (prothrombin time, activated partial thromboplastin time, fibrinogen, antithrombin, factor VIII, thrombin time, anti-factor Xa) across diverse methodologies. DESIGN: Samples with different concentrations of fondaparinux (0, 0.4, 0.8, and 2.0 microg/mL) were sent to laboratories participating in the College of American Pathologists Comprehensive Coagulation proficiency survey (N = 898). Laboratory-specific methods were used to assay coagulation parameters. RESULTS: Prophylactic or therapeutic fondaparinux prolonged the prothrombin time by approximately 1 second and the activated partial thromboplastin time by 4 to 5 seconds, and reduced factor VIII from 119% to 107% and 102%, respectively. Supratherapeutic fondaparinux reduced factor VIII to 85%. The activated partial thromboplastin time was prolonged in 19%, 29%, and 52% of laboratories with prophylactic, therapeutic, and supratherapeutic fondaparinux levels, respectively. Fibrinogen, antithrombin, and thrombin time assays did not show clinically significant changes. When measuring fondaparinux concentration using an anti-factor Xa assay, the most accurate results were obtained when fondaparinux was used as the calibrator. CONCLUSIONS: Fondaparinux, even in prophylactic doses, slightly prolongs the prothrombin time and activated partial thromboplastin time and can interfere with factor VIII assays, but it has no clinically relevant effect on fibrinogen, antithrombin, or thrombin time. A fondaparinux standard curve should be used for reporting fondaparinux levels using an anti-factor Xa assay.

Anticoagulants↗

PubMed1997

Monitoring warfarin therapy in patients with lupus anticoagulants.

BACKGROUND: Recommended therapeutic international normalized ratios (INRs) for oral anticoagulation in patients with lupus anticoagulants who sustain a thromboembolic event are controversial. Patients with lupus anticoagulants often have a prolonged prothrombin time, which may complicate management of anticoagulant therapy. OBJECTIVES: To determine the validity of the INR as a monitor for warfarin therapy in patients with lupus anticoagulants and to investigate alternate approaches to monitoring warfarin therapy in these patients. DESIGN: Prospective case series. SETTING: Tertiary care hospital. PATIENTS: 34 patients with lupus anticoagulants. MEASUREMENTS: Prothrombin times were determined by using several thromboplastins, and INRs were calculated for the patients receiving warfarin. Factor II levels, chromogenic factor X levels, and prothrombin-proconvertin times were determined for patients receiving warfarin. RESULTS: For patients with lupus anticoagulants who were not receiving warfarin, prothrombin times were often elevated and varied significantly with different thromboplastins. Individual thromboplastins differed in sensitivity to the presence of a lupus anticoagulant. For patients receiving warfarin, INRs obtained by using different thromboplastins greatly varied and often overestimated the extent of anticoagulation. Chromogenic factor X levels and prothrombin-proconvertin times correlated well with each other and with established therapeutic ranges. CONCLUSIONS: Lupus anticoagulants can influence prothrombin times and lead to INRs that do not accurately reflect the true level of anticoagulation. Use of the INR to standardize prothrombin times is invalid for some patients with lupus anticoagulants. To prevent supratherapeutic or subtherapeutic anticoagulation, these patients must be individually monitored with a test that is insensitive to lupus anticoagulants.

Adolescent↗

PubMed1999

Obtaining blood samples for coagulation studies from a normal saline lock.

OBJECTIVES: To determine the amount of blood that should be discarded from a peripheral normal saline lock, a capped-off intravenous port, before a blood sample is obtained for determination of activated partial thromboplastin time from patients being treated with heparin. METHODS: A prospective, quasi-experimental design was used with 32 patients. A blood sample was obtained via venipuncture from each patient to serve as the control for that patient. The normal saline lock was flushed with 2 mL of normal saline. Four consecutive 3-mL blood samples were obtained directly from the normal saline lock, representing samples obtained after discard volumes of 0, 2, 4, and 6 times the dead space of the catheter and extension set (1.5 mL). Activated partial thromboplastin times for the venipuncture blood sample were compared with the times for the blood samples obtained from the normal saline lock. RESULTS: The only significant difference (P = .02) was that activated partial thromboplastin time was 15% higher in the blood sample obtained from the normal saline lock with no blood discarded than in the venipuncture blood sample. CONCLUSIONS: Nurses can obtain accurate measurements of activated partial thromboplastin time with blood samples obtained from normal saline locks by first discarding a volume of blood equal to 2 times the dead space of the catheter and extension set. Obtaining blood samples in this manner reduces patients' discomfort due to repeated venipuncture and diminishes blood loss.

Adult↗

PubMed1999

Reliability of an intravenous intermittent access port (saline lock) for obtaining blood samples for coagulation studies.

BACKGROUND: Patients admitted to rule out myocardial infarction often receive a heparin infusion that requires measurement of partial thromboplastin time every 6 to 8 hours until coagulation values stabilize. If the patient's acuity at admission does not necessitate placement of arterial or central catheters, insertion of an intermittent intravenous access port (saline lock) would decrease the need for frequent venipuncture. Many studies on obtaining blood samples via arterial and central catheters have been reported, but no reports have described the method of using a saline lock or the amount of blood discarded during that procedure. OBJECTIVE: To evaluate the efficacy of inserting a saline lock specifically for obtaining blood samples and to determine the amount of blood that must be discarded in order to obtain prothrombin and partial thromboplastin times that match the values from blood samples obtained via venipuncture. METHODS: Coagulation values determined with 2 consecutive blood samples obtained via the saline lock after the first 0.5 mL of blood withdrawn was discarded were compared with measurements determined with a blood sample obtained via venipuncture. RESULTS: Prothrombin and partial thromboplastin times were not significantly different among the 3 blood samples. CONCLUSION: The untoward effects of frequent venipunctures to obtain blood samples for measurement of prothrombin and partial thromboplastin times can be lessened by using an 18-gauge saline lock to obtain blood samples and discarding the first 0.5 mL of blood withdrawn before the samples for coagulation studies are collected.

Adult↗

PubMed1992

Comparison of PT and aPTT values drawn by venipuncture and arterial line using three discard volumes.

BACKGROUND: Blood samples obtained through heparinized arterial catheters are used routinely for a variety of laboratory tests. Accuracy of coagulation studies performed from samples obtained in this fashion continues to be questioned, particularly in regard to the minimum discard volume necessary to clear the catheter of heparinized solution. OBJECTIVE: To examine differences between prothrombin time and activated partial thromboplastin time values obtained from blood drawn by venipuncture and from an indwelling intra-arterial line using three discard volumes. METHODS: Prothrombin time and activated partial thromboplastin time samples were drawn by venipuncture from 41 critically ill adult patients. Simultaneously, three consecutive blood samples of 2.3 mL were drawn from the arterial line after an initial discard volume of 3 mL (discard volumes of 3.0, 5.3 and 7.6 mL). RESULTS: Significant differences were found between arterial and venous prothrombin time values for the 3-mL discard volume group, as well as between arterial and venous activated partial thromboplastin time values for all three discard volume groups (paired t-test, Bonferroni correction). CONCLUSION: We recommend that when drawing prothrombin time and activated partial thromboplastin time samples from an arterial line, a 5.3-mL discard volume be used.

Adult↗

PubMed1990

The dependence of the International Sensitivity Index on the coagulometer used to perform the prothrombin time.

This study was designed to detect any effect that different types of coagulation instrument may have on the International Sensitivity Index (ISI) of a thromboplastin. Manufacturers of commercial thromboplastins now calibrate their reagents against the World Health Organization international reference preparation to assign them an ISI. This enables the prothrombin time (PT) estimated with that reagent to be expressed as an International Normalised Ratio (INR). One batch of Thromborel S was calibrated against the Australasian Reference Thromboplastin (ART). The Thromborel S was used on three photo-optical instruments, the Automated Coagulation Laboratory (ACL) (Instrumentation Laboratory), the Cobas Fibro (Roche), and the Coag-a-Pet (General Diagnostics). PTs using ART were performed manually using the reference method. The ISIs calibrated in our laboratory when the ACL and Cobas Fibro were used were not significantly different at the 95% level, being 1.102 +/- 0.018 and 1.134 +/- 0.022 respectively. The ISI with the Coag-a-Pet of 1.223 +/- 0.023 was significantly different to that of the ACL and the Cobas Fibro at the 95% level. The flowcharts for a computer program to perform the necessary calculations are provided. The program allows for the entry and editing of data from the calibration procedure, and provides a mean normal PT and normal range, the ISI and 95% confidence limits of the calibration, and a chart for the conversion of the test PTs to INRs. The authors have made available an IBM compatible program for the calibration of thromboplastins.

Blood Coagulation Tests↗

PubMedDate not supplied

[Control of oral anticoagulation. Current concepts].

The main objective of this short review is to bring into focus the most relevant of the recent advances in prothrombin time standardization and analyze the recommendations of the World Health Organization (WHO) for monitoring patients with thrombotic disorders under treatment with oral anticoagulant drugs. The prothrombin time (PT) is indicative of the proper therapeutic range in patients receiving oral anticoagulant drugs; however the reliability of the results will depend on the source and nature of the thromboplastin used. Different normal and therapeutic rangers are frequently observed when different brands of thromboplastin reagents and/or methods are used. The WHO, in conjunction with the International Committee of Thrombosis and Hemostasis and the International Committee of Standardization in Hematology, has recommended a calibration scheme for thromboplastin standardization with special reference for anticoagulant monitoring. Instead of reporting patient values, either in seconds or percent activity, WHO recommends the PT results in terms of an international normalized ratio (INR). This is obtained by formula: INR = RC in which R is the patient's PT and C is the international sensitivity index (ISI) of the thromboblastine employed. The INR represents the PT that would be obtained if it were performed with the WHO thromboplastin reference preparation. We suggest that these new concepts should be implemented by both laboratory and clinical professionals with the purpose of improving the effectiveness and safety of oral anticoagulation.

Administration, Oral↗

PubMed1987

Oral anticoagulant therapy control: evidence that INR expression improves the inter-laboratory comparability of results--the Bologna oral anticoagulant control exercise.

The aims of the present study were: 1) interlaboratory normalization of prothrombin time (PT) testing for anticoagulant therapy control through calibration of customary thromboplastins against international reference materials, and 2) "on field" validation of the advantages offered by expression of results as International Normalized Ratio (INR) as opposed to percentage activity. PT tests were carried out over 8 days on the same normal subjects (16) and patients on oral anticoagulants (48) in the 9 laboratories of the Bologna area. The use of customary thromboplastins and coagulometers was maintained in all labs throughout the study. The main results were: 1) the interlaboratory CV of the prothrombin ratios obtained for each sample with all customary thromboplastins (5 different brands) was 15%, but was reduced to levels of 5.8 to 8.9 when using constant thromboplastin brands and batches; 2) the International Sensitivity Index (ISI) values obtained in the different labs were only slightly influenced by the use of different coagulometers; 3) comparable ISI values were obtained through direct calibration with the international reference material and through intermediate calibration with a locally selected standard; 4) use of INR values instead of percentage activity greatly reduced interlaboratory variability and significantly improved uniformity of anticoagulation level measurements, thus reducing the possibility of erroneous prescriptions. The Bologna exercise is therefore of educational value for laboratory and community doctors of the area in understanding and accepting the INR system.

Administration, Oral↗

PubMed1983

Report of the fifth homozygous patient with factor VII Padua defect.

A new patient with factor VII Padua abnormality is presented. The propositus is a 70 old man who showed a mild bleeding tendency characterized by occasional epistaxis and a laboratory pattern of prolonged prothrombin time corrected by normal serum, normal partial thromboplastin time and normal Thrombotest. Factor VII activity was 7% using rabbit brain thromboplastin and 105% of normal using ox-brain thromboplastin. Intermediate levels were found by using thromboplastin of human origin. Factor VII cross-reacting material was normal. Parents were not consanguineous but both came from the same area. Two children of the propositus were found, as expected, to be homozygous for the abnormality. No relationship could be traced between the propositus and the other homozygous patients already reported. However, the patient came from the same geographic area, namely the Piave river valley in northeastern Italy. The discovery of the present patient, the fifth in four years, indicates that the defect might be more frequent than originally assumed.

Aged↗

PubMed1978

[Trial of an automatic apparatus for coagulation : Auto-Fi Dade (author's transl)].

Auto-Fi Dade has been used for thromboplastin time, activated partial thromboplastin time, fibrinogen determination and a few determinations of factors V, VII + X, II and VIII. The results of the thromboplastin time, using Dade Tromboplastin or thromboplastins from two other commerical firms, show a coefficient of variation (CV) ranging from 1.11 to 3.43% for short times and 1.97 to 2.64% for longer times.

Afibrinogenemia↗

PubMed1981

[Laboratory control of anticoagulant treatments (author's transl)].

Laboratory control of anticoagulant treatments is still unclear, in spite of 25 years experience, better knowledge of the mechanisms of action of the different drugs, and the new techniques available. In general, laboratory control includes a test specific for the action of the drug involved, associated or not with a test that reflects global coagulability. During heparin treatment, the association of recalcification time or activated partial thromboplastin time with heparin levels is recommended. A weekly platelet count can eliminate heparin-induced thrombocytopenia. During oral anticoagulant treatment, the association of thromboplastin time or Owren's thrombotest with activated partial thromboplastin time is indicated. The therapeutic ranges for thromboplastin times are different according to the reagents used and should be specified by the laboratory since present methods of standardization are not yet satisfactory.

Anticoagulants↗

PubMed1994

Evaluation of recently described tests for detection of the lupus anticoagulant.

It is known that lupus anticoagulants (LA) are antibodies which interfere with phospholipid-dependent coagulation tests, but due to the heterogeneity of LA and the differences in sensitivity of reagents and tests, the diagnosis of LA remains difficult. Recently, Triplett et al. (26) have proposed a new test based on two venoms, Textarin (T) and Ecarin (E), that activate prothrombin but differ in their phospholipid requirements. By testing this new assay we have evaluated 36 patient plasmas containing LA according to standard tests (activated partial thromboplastin time, dilute Russell viper venom time and platelet neutralization procedure) and our results confirm a high sensitivity for LA of the T/E test. In addition, we observed a greater sensitivity of the tissue thromboplastin inhibition test using a recombinant thromboplastin instead of a human placenta thromboplastin. Our study also showed that the T/E test seems to be a useful assay in confirming the diagnosis of LA in patients with an unexplained prolonged APTT.

Adult↗