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PubMed1992

Imprecision of prothrombin time monitoring of oral anticoagulation. A survey of hospital laboratories.

Prothrombin time monitoring of oral anticoagulation is highly dependent on the tissue thromboplastin used. In the United States, patients have received a higher level of anticoagulation because of the use of a less sensitive thromboplastin. Many advocate the use of an International Normalized Ratio to rectify this problem. Laboratory supervisors from all acute care hospitals in Massachusetts were surveyed to determine the disparity in thromboplastin use and reporting practices for prothrombin time testing. Eighty-eight of 103 (86%) hospitals responded. Fifty-eight lots from six manufacturers of thromboplastin were in use. The International Sensitivity Index of these lots ranged from 1.89 to 2.74. Ninety-nine percent of hospitals reported prothrombin times in raw seconds. Only 5% reported an International Normalized Ratio. Sixteen different coagulation instruments were in use. Close to 70% of laboratory supervisors had little or no understanding of the significance of an International Sensitivity Index or an International Normalized Ratio. The management of oral anticoagulation appears far less precise than had been believed. Prothrombin times in the same individual from different laboratories may have poor correlation. Based on the level of understanding of laboratory supervisors, extensive education will be necessary to change practices and improve accuracy and comparability of prothrombin time testing.

Administration, Oral↗
PubMedDate not supplied

Fat emulsion effects on prothrombin time in warfarin anticoagulated patients: an in vitro study.

The effect of lipid emulsions on prothrombin time in blood from anticoagulated patients was determined. Blood samples were obtained from 23 patients therapeutically anticoagulated with warfarin (prothrombin time 1.3-2.0 x control). Varying amounts of an intravenous lipid emulsion (Intra-lipid) were added to the blood to simulate concentrations seen in vivo with a constant lipid infusion. The prothrombin time was measured on the plasma from these samples and compared to the prothrombin time of the plasma samples without lipid. The mean decrease in prothrombin times were: 0.29 sec at 50 micrograms/ml, 0.23 sec at 100 micrograms/ml, and 0.29 sec at 200 micrograms/ml. All concentrations showed a statistically significant decrease (p less than 0.05) when compared to the control by the Scheffe test. Lipid emulsions appear to decrease the prothrombin times in anti-coagulated patients. The differences however, were small and not of clinical significance at the concentrations tested.

Fat Emulsions, Intravenous↗
PubMed1979

The varied sensitivity of partial thromboplastin and prothrombin time reagents in the demonstration of the lupus-like anticoagulant.

An acquired inhibitor of blood coagulation, similar to that described in patients with Systemic Lupus Erythematosus (SLE), was detected during routine coagulation screening in 10 patients who did not meet the criteria for a diagnosis of SLE. The lupus-like anticoagulant (LLAC) was diagnosed on the basis of prolonged activated partial thromboplastin time (APTT) and/or prothrombin time (PT) which failed to correct when patient plasma was added to normal plasma; an additional criterion was an abnormal tissue thromboplastin inhibition test. No patient had a specific inhibitor directed against factors VIII and IX. Demonstration of LLAC was highly dependent upon the type of reagents adopted in the APTT and PT: the abnormality was detected consistently by one reagent only. One-stage assays of factors VIII and IX were characteristic of the presence of an inhibitor, showing non-parellel dose-response curves or decreased activity at low dilutions which were partially corrected at higher dilutions. Although 7 patients were free of abnormal bleeding, unequivocal signs of haemorrhagic tendency after a surgery were present in the remaining 3 patients. The findings suggest that LLAC is a non-exceptional cause of prolonged coagulation screening tests, and that it may sometimes be associated with impaired haemostasis.

Adolescent↗
PubMed1989

Bleeding in outpatients treated with warfarin: relation to the prothrombin time and important remediable lesions.

PURPOSE: To determine the relation of bleeding to prothrombin times and important remediable lesions in outpatients treated with warfarin. PATIENTS AND METHODS: An inception cohort of 565 patients starting outpatient therapy with warfarin on discharge from a university hospital was assembled. Detailed records of outpatient prothrombin times were obtained for 103 of 130 case subjects with major or minor bleeding and for 117 control patients without bleeding. A nested case-control design was used to evaluate the association of bleeding with temporally related prothrombin times; odds ratios were estimated using multivariate logistic regression analysis to control for known predictors of major bleeding. The relation of bleeding to important remediable lesions was determined in all 130 cases of bleeding. RESULTS: For each 1.0 increase in the prothrombin time-to-control ratio, the odds ratio for major bleeding during the week after a prothrombin time measurement increased 80%; the odds ratio for minor bleeding increased 50%. These odds ratios were lower during the first month of therapy and higher thereafter. Bleeding was related to important remediable lesions in 49 of 130 cases (38%), but these lesions were unknown before bleeding in only 22 cases (17%). The mean prothrombin time rose sharply at the time of bleeding in patients without important remediable lesions, but not in patients with lesions. New, previously unknown lesions (including nine malignancies) were discovered in 20 of 59 case subjects (34%) with gastrointestinal bleeding or hematuria, but in only two of 71 case subjects (3%) with other bleeding (p less than 0.001). CONCLUSION: Our results provide a valid quantitative basis for estimating the odds of bleeding in relation to the prothrombin time and the yield of diagnostic evaluation in patients with bleeding.

Aged↗
PubMed1990

Prothrombin time as an index of mortality in kwashiorkor.

Prothrombin time, serum albumin, aminotransferases and liver size were evaluated in 40 consecutive cases of kwashiorkor. Eleven (27.5%) of the 40 patients died. Eight out of the 11 patients who died had a prolonged prothrombin time of more than 3 s above the control compared to only 4 out of the 29 who survived (p = 0.005). Mean serum aspartate aminotransferase (AST), alanine aminotransferase (ALT) albumin, globulin and liver size were abnormal but similar in both groups. These results may indicate a predictive mortality value of prothrombin time in kwashiorkor.

Bacterial Infections↗
PubMed1977

The prediction of prothrombin time system performance using secondary standards.

A method for the comparison of prothrombin time systems using single large lots of lyophilized plasma in the College of American Pathologists Surveys is presented. Systematic biases for prothrombin time methods as well as for thromboplastins have been measured, and their use allows a very accurate (within 2.25%) prediction of the prothrombin time for the great number of prothrombin time systems presently being used in the United States.

Blood↗
PubMed1990

Randomized prospective trial comparing the native prothrombin antigen with the prothrombin time for monitoring oral anticoagulant therapy.

The dosage of the anticoagulant warfarin sodium is based upon the prolongation of the prothrombin time into an optimal therapeutic range. We have developed a new assay for the native prothrombin antigen that measures the fully gamma-carboxylated prothrombin using a radioimmunoassay. Based on preliminary data that indicated that the native prothrombin antigen predicted both bleeding and thrombotic complications more accurately than the prothrombin time in patients anticoagulated with warfarin sodium, we have performed a randomized prospective trial comparing the complication rate in warfarin-treated patients monitored with the native prothrombin antigen or the prothrombin time. Patients with indications for anticoagulation were randomized to be monitored by the native prothrombin antigen (therapeutic range, 12 to 24 micrograms/mL) or the prothrombin time index (therapeutic range, 1.5 to 2.0). Of the prothrombin time group (N = 80), seven (8.8%) had bleeding or thrombotic complications, with a complication rate of 9.5%/patient-year. In the native prothrombin antigen group (N = 76), one subject (1.3%) had a bleeding complication. The complication rate per patient-year was 1.5%. These results indicate an 85% reduction in the complication rate of the native prothrombin antigen group compared with the complication rate of the prothrombin time group. This difference is statistically significant by the Fisher exact test (P = .037) and by Kaplan Meier survival analysis (P = .040). This study suggests that the use of the native prothrombin antigen assay has the potential to decrease the complications associated with anticoagulation therapy with warfarin sodium.

Humans↗
PubMed1990

Serial prothrombin time as prognostic indicator in paracetamol induced fulminant hepatic failure.

OBJECTIVE: To find out whether changes in the daily prothrombin time are of prognostic importance in patients with paracetamol induced fulminant hepatic failure. DESIGN: Retrospective study. SETTING: The Liver Unit, King's College Hospital, London. PATIENTS: 150 Consecutive patients with paracetamol induced fulminant hepatic failure admitted between October 1986 and February 1989. MAIN OUTCOME MEASURE: Death. RESULTS: Of the 150 patients, 72 (48%) died. In all, 34 of the 37 (92%) patients with a peak prothrombin time of greater than or equal to 180 seconds died as did 20 of the 41 (49%) with a time of 130-179 seconds, nine of the 25 (36%) with a time of 90-129 seconds, and nine of the 47 (19%) with a time of less than 90 seconds. Of the 42 patients with a continuing rise in prothrombin time between days 3 and 4 after overdose, 39 died (93%) compared with 21 of the 96 (22%) in whom the prothrombin time fell. CONCLUSIONS: These data indicate that a continued increase in prothrombin time on day 4 after overdose and a peak prothrombin time of greater than or equal to 180 seconds identify at an early stage those patients with a less than 8% chance of survival. Liver transplantation should be considered in patients meeting either of these criteria.

Acetaminophen↗
PubMed1975

Investigation and standardization of prothrombin times in chickens.

This investigation was undertaken to standardize the determination of the one-stage prothrombin time for use with chickens. Homologous thromboplastin was essential and the most active thromboplastin was obtained from chickens four-weeks old or younger. Acetone-dried brain powder could be stored for at least 4 months at -15 degrees C. without loss of activity. Extraction of brain powder with 0.025 M CaCl2 at 42 degrees C. gave better thromboplastic activity than the standard extraction with physiological saline at room temperature. Thromboplastin solutions could be stored in ice water for only 6 hours without loss of activity. Citrate concentration had to be increased from the usual 0.10 M to 0.18 M to prevent premature clotting of plasma. Plasma donor age had no effect on the prothrombin times. Freezing and thawing as well as storage of plasma in the frozen state increased the prothrombin times. Using the best conditions, the mean prothrombin time for 1200 birds determined over a 6-month period was 9.4 sec. with an individual range of 7.18-11.4 sec. This represents a significantly lower prothrombin time with lower variability than that reported in the literature.

Age Factors↗
PubMed1992

The precision of duplicate prothrombin time and partial thromboplastin time assays in neonates.

An evaluation of duplicate prothrombin time (PT) and activated partial thromboplastin time (PTT) assays was performed in 277 neonatal samples. Performance criteria were analyzed to determine whether single vs duplicate procedures could be utilized reliably without exposing the neonates to the risk of erroneous PT and PTT results. In addition, we evaluated whether this approach might decrease phlebotomy and hence reduce the number of blood transfusions administered. For PT assays, 97.5% (270/277) of the duplicate results were different by 1 second or less. Only 2.5% (7/277) differed by 3 seconds. For PTT duplicates, 75.0% (207/277) of the values were different by 2 seconds or less and 13.0% (36/277) by 2 to 4 seconds. An additional 12.3% (34/277) were discrepant by as many as 4 seconds. The largest discrepancies occurred in specimens with markedly elevated PT and PTT results, indicative of a significant coagulopathy. In addition, heparin neutralization was performed successfully in 22 neonatal blood specimens showing either partial or full correction of PTT values due to heparin specimen contamination. This study indicates that single PT and PTT assays as well as heparin neutralization tests can be accurately performed and may be able to reduce blood donor exposure by as many as one blood transfusion every 2 to 3 days of hospitalization.

Heparin Antagonists↗
PubMed1978

[A micro-method developed for prothrombin time assay (author's transl)].

Prothrombin time was measured by a newly developed micro-method using a plastic film available in the market (PARAFILM, American Can. Co.). The comparative study of this micro-method with that of Quick in rats disclosed a good correlation, with correlation coefficient of 0.951, supporting the usefulness of the method for examination of blood coagulability. The new method gave the physiological values of 9.8 sec in rabbits, 12.5 sec in dogs, 13.3 sec in mice, 14.8 sec in cats and 16.0 sec in rats, respectively. Among them, guinea pigs took the longest time of 25.3 sec for the coagulation.

Animals↗
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↗
PubMed1987

Study on a new chromogenic substrate for the prothrombin time determination.

The aim of our study was to evaluate the possibility of using a chromogenic substrate for the prothrombin time determination. The reagent used by us (Chromoquick) is composed of a human placenta thromboplastin and chromogenic substrate (Tos-Gly-Pro-Arg-5-amino-2-nitrobenzoic acid-isopropylamide), calcium chloride and a buffer. Normal subjects, patients with liver disease, patients on oral anticoagulant therapy, patients on heparin therapy, heterozygous and homozygous patients for prothrombin complex defects and other miscellaneous conditions have been investigated. The results of chromoquick have been related with standard prothrombin time obtained using a human placenta thromboplastin (Thromborel) and rabbit brain and lung thromboplastin (Simplastin). The normal range was 18-23 s for chromoquick and 13.5-15.5 s for the standard prothrombin times using Thromborel and Simplastin. In all groups of patients examined we noticed a significant correlation between the chromogenic and the classic prothrombin times with r values varying between +0.505 and +0.947. The statistical significance resulted from p values varying between less than 0.05 and less than 0.001. Only in the case of some heterozygotes for prothrombin complex factor defects the values obtained have not been unequivocal in the sense that in a few instances the heterozygotes seemed to escape detection. Therefore, it seems that the introduction of chromogenic substrates in laboratory practice for the prothrombin time determination is possible and can offer considerable advantages like standardization and automation. The only disadvantage may be caused by costs involved.

Acenocoumarol↗
PubMed1986

A comprehensive evaluation of the performance of duplicate prothrombin time and activated partial thromboplastin time assays.

An evaluation of the performance of duplicate prothrombin time (PT) and activated partial thromboplastin time (aPTT) assays was undertaken to develop analytical duplicate performance criteria in order to quantitate the risks associated with singlet versus duplicate procedures. Data were retrospectively collected from two hospital laboratories using two different coagulation systems. Included in the study were 6,391 patient samples; 3,047 PT, 3,334 aPTT, for a total of 12,782 data points. If a difference between duplicates of 5% or less is deemed analytically (or clinically) insignificant for PT, then fewer than 1% of the samples analyzed by either laboratory would require duplicates. If a difference between duplicates of 15% or less is deemed analytically (or clinically) insignificant for aPTT, then fewer than 2% of samples would exceed this limit for laboratory A, but 6.0% of samples from laboratory B exceeded this limit.

Blood Coagulation Tests↗
PubMed1991

An analysis of duplicate testing of prothrombin time and activated partial thromboplastin time assays.

An evaluation of duplicate prothrombin time (PT) and activated partial thromboplastin time (aPTT) assays determined by the MCA 110 coagulation analyzer was undertaken to develop analytical duplicate performance criteria to quantitate the risks associated with single versus duplicate procedures. Included in the study were 1,277 patient samples. On the basis of the currently recommended therapeutic range for prothrombin ratios, a variation of approximately 10% or more between duplicates was considered to be unacceptable. For aPTT assays, the recommended therapeutic range for heparin therapy was usually 1.5 to 2.5 times the baseline value, and variations of up to 25% might be considered acceptable. With these relatively lenient criteria, approximately 2% of PT and 1.3% of aPTT assays had differences between duplicate values that were unacceptable. From this data the authors concluded that the frequency of errors produced by single estimations was too great for satisfactory clinical practice.

Humans↗