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PubMed1996

Prothrombin time: one tube or two.

This study compares the prothrombin times (PTs) and calculated international normalized ratios (INRs) from first and second evacuation blood tubes to determine the clinical importance of using a second tube specimen for protime coagulation studies. The National Committee for Clinical Laboratory Standards (NCCLS) currently recommends that all coagulation studies be done on a second or later drawn blood tube. For patients on long-term anticoagulation therapy, this often requires that first blood tubes be drawn and discarded at each prothrombin evaluation. In this prospective study, a first and second evacuation blood tube was drawn from 343 outpatients who had a physician-ordered prothrombin time test performed. There was no statistically significant difference in the paired PT or calculated INR from any of the first and second tubes. The average difference in the INR from tube 1 to tube 2 was 2% (standard deviation [SD] 1.1%). In this sample of outpatients, the use of a second tube for PT testing was not clinically justified.

Ambulatory Care↗
PubMed2001

Patient self-testing of prothrombin time after hip arthroplasty.

We determined whether total hip arthroplasty (THA) patients could test their own prothrombin time reliably over 6 weeks of anticoagulation prophylaxis with a portable device that measures prothrombin time and whether self-testing would improve or maintain the quality of care at a lower cost than our standard procedure. Forty-six THA patients participated in the study and were compared with a matched group managed with our standard protocol using a home health-care nurse. Seven patients (15%) could not be trained to obtain the blood sample, and others required multiple finger sticks to obtain valid results. However, the results from the 29 patients completing the study showed high reliability when compared with results obtained through standard protocol. Self-testing saved about $260 per patient over the cost of venipuncture. Patient self-testing of prothrombin time using the device in this study is reliable and cost-effective for monitoring the anticoagulation status after THA in a select group of elderly patients.

Adult↗
PubMed1992

Within-subject and between-subject biological variation of prothrombin time and activated partial thromboplastin time.

The within-subject and between-subject biological variation of prothrombin time (PT) and activated partial thromboplastin time (APTT) have been studied in a group of 19 women and 20 men over a period of 9 months. All measurements were performed with a mechanical coagulometer. The between-subject coefficients of variation were 6.8% for PT and 8.9% for APTT. The medians and the 90th percentiles of within-subject coefficients of variation were 1.7% and 5.9%, respectively, for PT, and 0.0% and 6.1% for APTT. These data were used to calculate the critical difference for significant change detection and the desirable between-day imprecision.

Adult↗
PubMed1998

Perioperative reliability of an on-site prothrombin time assay under different haemostatic conditions.

Perioperative use of laboratory coagulation assays is limited by the delay in obtaining results. The management of haemostasis during major surgical procedures requires rapid and accurate measurement of the prevailing coagulation status. In this prospective study, we have evaluated the reliability of on-site prothrombin time assessed by the portable coagulation monitor CoaguChek-Plus compared with standard laboratory assays during elective non-cardiac surgery. Sixty-two patients were assigned to one of three groups: group A = normal preoperative coagulation where minor intraoperative blood loss is expected; group B = normal preoperative coagulation where major intraoperative blood loss is expected; and group C = preoperative anticoagulation and minor intraoperative blood loss expected. On-site prothrombin time and laboratory prothrombin time showed poor correlation in group A (r2 = 0.24; bias (2 SD) 1.80 (3.34) S) and group B (r2 = 0.30; 1.43 (3.12) S). The correlation in group C was better (r2 = 0.71; 1.41 (1.92) S). We conclude that prothrombin time measured with the CoaguCheck-Plus monitor did not appear to be suitable for the management of haemostasis.

Blood Loss, Surgical↗
PubMed1994

The response of Quick's prothrombin time test to oral anticoagulation. Influence of thromboplastin source and calcium chloride concentration.

The response of the prothrombin time to oral anticoagulant treatment depends on the thromboplastin reagent and method of testing. A prothrombin time assay system may be characterized by its international sensitivity index (ISI) with which a coumarin-treated patient's international normalized ratio can be calculated. Both the anticoagulant (sodium oxalate or sodium citrate) and calcium chloride concentrations influenced the ISI. An ISI of 2.0 was obtained for Quick's prothrombin time assay using rabbit brain thromboplastin. Replacing rabbit brain by human brain thromboplastin (Aggeler's method) resulted in an ISI of 1.3. The results described herein are mainly of historical interest and may assist in the interpretation of anticoagulation intensity in early American recommendations.

Administration, Oral↗
PubMed1986

[Methodological aspects of the photometric determination of prothrombin time using chromogenic substrates].

A method for photometric determination of prothrombin time (PT) with a chromogenic peptide as substrate is described. The reagent contains human placental thromboplastin, a chromogenic substrate, calcium, a heparin antagonist and buffer. The new prothrombin time method has been calibrated against international reference preparations for thromboplastin. The reagent is sensitive to deficiency of all coagulation factors of the extrinsic pathway. However, it is not sensitive for heparin up to 1 IU/ml. The precision of this fast and simple method is comparable to that of mechanised assays for clinical chemistry.

Blood Coagulation↗
PubMed2003

[Control of anticoagulant therapy with portable prothrombin time device in patients with mechanical heart valve prostheses: two-year follow-up].

BACKGROUND: Monitoring patients on oral anticoagulation is essential to prevent haemorrhage and recurrent thrombosis, but it is still difficult. We studied a group of 348 patients with mechanical heart valve prostheses to verify whether the use of a new portable prothrombin time device might improve the management of oral anticoagulant therapy. METHODS AND MATERIAL: We used a new portable prothrombin time device to check the anticoagulation therapy in a group of 348 patients with mechanical heart valve prostheses to validate its results by comparing to routine I.N.R. determinations (28 pts) and verify its user-friendliness by a face-to-face interview. Furthermore, the incidence of haemorrhagic and thromboembolic events has been studied by a two-year follow-up. RESULTS: Pearson correlation indicated an R2 = 0.9 between I.N.R. values determined by routine or by a new portable prothrombin time device. All patients agreed to replace the routine I.N.R. determinations with those by the new procedure, particularly female, young and those with usually difficult blood collections. During the two-year follow-up period, 21 haemorrhagic (2.6/100/patients/year) and 5 thromboembolic events (0.6/100/patients/year) occurred; but neither replaced valves' thrombi nor fatal events were found out. CONCLUSIONS: I.N.R.s determined using a new portable prothrombin time device are convincing as routine determinations. Such new procedure improves the quality of life, and the therapeutical range of anticoagulation is maintained safer and longer than by routine determinations. These results suggest that the control of anticoagulation in patients to a set I.N.R. therapeutic range is improved by using portable prothrombin time device in expert anticoagulation clinics, such improvement may result in reducing mortality as well as morbidity in patients treated with oral anticoagulants.

Anticoagulants↗
PubMedDate not supplied

Why is the standardization of prothrombin time a problem?

The standardization of prothrombin time (PT) has been a problem for more than 50 years; by applying the methods to the same clinical material the analysis may explain why. The initial standardization by 2--3 times normal clotting time by Quick's PT assay did not standardize presently used PT assays. The ratio method accepted by the WHO in 1977 was not satisfactory because the intercept was neglected. The revised ratio method (WHO 1983) recommended calibration between log clotting times of normal and abnormal plasmas and a simplified conversion into ratios. However, by including a high proportion of normal plasmas (up to 1/3 of abnormal) an erroneous calibration material was introduced; the conversion from clotting times into ratios was also more complex than predicted. The international sensitivity index, which is based on the simplified method, produced international normalized ratios (INR) that were not more standardized than not corrected ratios. Not corrected coagulation activities showed poor standardization due to the different sensitivity of assays for the protein induced by vitamin K absence (Pivka) inhibitor. The corresponding therapeutic ranges of INR and coagulation activities covered 70 and 10--20% of their scales, respectively. Standardization by Pivka-corrected coagulation activities against an international reference assay may be the preferable method.

Blood Coagulation Tests↗
PubMed1971

The "therapeutic range" of the one-stage prothrombin time in the control of anticoagulant therapy: the effect of different thromboplastin preparations.

Commercially available thromboplastin reagents and two human brain preparations have been compared using the one-stage prothrombin time and plasma samples from patients receiving long-term oral anticoagulant therapy. Considerable variation is noted between various thromboplastins using the same plasma sample. The commercially available thromboplastins give shorter prothrombin times than do human brain preparations. With the latter, the "therapeutic range" is represented by a prothrombin time of about 1.8 to 3.0 times the normal control value, whereas with commercial preparations the "therapeutic range" is about 1.25 to 1.75 times normal. The implications of these observations are discussed; the desirability of standardization of the one-stage prothrombin time is emphasized.

Anticoagulants↗
PubMedDate not supplied

A statistical and clinical evaluation of fingerstick and routine laboratory prothrombin time measurements.

STUDY OBJECTIVE: To compare prothrombin time measurements by fingerstick and routine laboratory methods. DESIGN: Prospective cohort study. SETTING: University-affiliated anticoagulation clinic. PATIENTS: Thirty-three patients receiving warfarin with stable anticoagulation for 3 months preceding the two studies. INTERVENTIONS: Groups 1 (17 patients) and 2 (16 patients) provided 150 and 125 paired samples, respectively, for fingerstick and routine laboratory analysis. The fact that no patient required a dosage change allowed for a clinical assessment. MEASUREMENTS AND MAIN RESULTS: Correlation and agreement between methods were good in group 1 but poor in group 2. Fingerstick results were less variable (smaller standard deviation and smaller coefficient of repeatability) in both groups. By analysis of discrepant pairs (25 in group 1, 63 in group 2), the routine laboratory results indicated dosage changes erroneously more often than did the fingerstick method. CONCLUSIONS: In these two trials, the fingerstick system was superior to the routine laboratory method in that it was more reliable (less variability and more repeatable) and less likely to indicate dosage changes erroneously.

Anticoagulants↗
PubMed1992

A comparison of the relative sensitivities of factor VII and prothrombin time measurements in detecting drug interactions with warfarin.

We have studied the comparative abilities of the prothrombin time and factor VII clotting activity, measured using a chromogenic assay, to detect drug interactions with warfarin. Pharmacokinetic and pharmacodynamic data were collected from studies involving the single administration of 25 mg of warfarin in the absence and presence of fengabin, cimetidine, ranitidine, and enoxacin. Fengabin caused changes in both the pharmacokinetics and pharmacodynamics of warfarin, whereas cimetidine and enoxacin only caused changes in its pharmacokinetics. Ranitidine had no effect on either the pharmacokinetics or pharmacodynamics of warfarin. In general, factor VII clotting activity showed greater sensitivity but also greater variability than the prothrombin time to changes in clotting activity. Consequently, factor VII clotting activity did not have greater discriminatory power than the prothrombin time in detecting drug interactions involving warfarin.

Adult↗
PubMed1980

Prothrombin times: an evaluation of four thromboplastins and four machines.

The prothrombin times of 63 patients on oral anticoagulant therapy were tested using 4 different thromboplastins; 2 rabbit brains (Simplastin & Ortho), human placenta (Thromborel) and human brain (Australasian Reference Thromboplastin--ART). Four machines measuring the one-stage prothrombin times were compared with the manual method. Each of the machines and thromboplastins showed highly reproducible and predictable results, but there were differences in thromboplastin sensitivities which would pose major therapeutic problems. A system of correcting ratios of different thromboplastins to a reference preparation would overcome these differences in thromboplastin sensitivities. All thromboplastins gave comparable results with the Clotek, MLA 600 and Coag-A-Pet machines and manual method. Cortek gave comparable ratios with the ART but not with any other thromboplastin.

Administration, Oral↗
PubMed2002

Variations of prothrombin time and international normalized ratio in patients treated with warfarin.

Prothrombin time is a standard screening test to monitor patients treated with oral anticoagulants. We hypothesize that INR measurements will not vary a lot within a given day in a given patient. The present study was thus conducted to compare the change of the international normalized ratio (INR) of prothrombin time (PT) within 1 day in patients treated with warfarin. Thirty such patients and nineteen healthy controls were enrolled into this study. PT was performed in four time points of a day in all subjects, two in the morning and two in the afternoon. The four INR values obtained were compared with each other to find little change in the series of time either in patients or in healthy controls. Neither were they affected by renal function, liver function, sex, age, hemoglobin, white cell count, platelet, treatment duration of warfarin, or alcoholic drinking. INR could be measured in any time of a day to have values equally valuable in clinical use.

Aged↗
PubMed1985

Inhibition of cold-promoted activation of the prothrombin time studies of new siliconized borosilicate collection tubes in normals and patients receiving warfarin.

Studies of the prothrombin time in normals and patients receiving oral anticoagulant therapy revealed a partial inhibition of the in vitro cold-promoted activation of Factor VII and shortening of the prothrombin time when blood was collected in a new commercial siliconized borosilicate tube (Becton-Dickinson, Rutherford, NJ, 6418 and 6419). The data collected with normal blood indicated that the cold-promoted activation was almost totally inhibited, while the patients had only a mean reduction of 50% of the cold-promoted activation. In pregnant patients there was no inhibition of the cold-promoted activation of the prothrombin time or Factor VII using the new siliconized tubes.

Blood Specimen Collection↗
PubMed1998

Laboratory control of oral anticoagulant therapy: preservation of prothrombin time specimens using a polypropylene collection system.

Previous studies have shown a marked time and temperature dependent shortening of the prothrombin time (PT) when blood is exposed to borosilicate (glass) or siliconized borosilicate tubes. Current recommendations are that samples for PT estimation should be tested within 2 h of collection. In this study using polypropylene collection tubes, blood obtained from 30 patients on oral anticoagulant therapy showed no significant change in International Normalized Ratio (INR) value after 24 h storage--either at 4 degrees C or room temperature. After 48 h. changes in INR values from refrigerated samples were still clinically insignificant. After 48 h storage at room temperature, however, a minority of samples showed an increase in INR value which may be of clinical importance. The range of INRs studied was 1.0-9.1. In a second evaluation, replicate specimens from 22 orally anticoagulated patients with INRs ranging from 1.0 to 9.6 showed no significant change after 24 h at either temperature--even when samples had been subjected to 30 min of gentle agitation prior to storage and analysis. Overall, the results indicate that when polypropylene collection tubes are used, prothrombin time specimens can be successfully preserved for up to 24 h at room temperature or up to 48 h when refrigerated.

Administration, Oral↗
PubMed1997

Recombinant factor VIIa corrects prothrombin time in cirrhotic patients: a preliminary study.

BACKGROUND & AIMS: Cirrhotic patients with a prolonged prothrombin time (PT) are known to have low levels of factor VII. Because the current modalities to correct this problem are not ideal, recombinant factor VIIa (rFVIIa) may be useful in correcting the prolonged PT observed in the coagulopathy of cirrhosis. The aim of this study was to evaluate the effectiveness of rFVIIa in nonbleeding volunteer patients with the coagulopathy of cirrhosis. METHODS: A preliminary, single-center, dose-escalation trial was performed. Cirrhotic patients with a PT of > 2 seconds above the upper limit of the reference value received an intramuscular injection of vitamin K. Ten patients whose PT did not correct to within 2 seconds above the control of the upper limit of the reference value were given three successive dosages of rFVIIa (5, 20, and 80 micrograms/kg) during a 3-week period. RESULTS: The mean PT transiently corrected to normal in all three dosage groups. No adverse effects were noted. There was no evidence of the induction of disseminated intravascular coagulation. CONCLUSIONS: This preliminary trial shows rFVIIa to be effective in transiently reversing the prolonged PT in a select group of nonbleeding cirrhotic patients. These preliminary observations support conducting a large-scale efficacy trial.

Adult↗