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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↗
PubMed1993

Paradoxic effect of multiple mild coagulation factor deficiencies on the prothrombin time and activated partial thromboplastin time.

Single coagulation factor deficiencies predictably prolong the prothrombin time (PT) and activated partial thromboplastin time (APTT) at levels below 35% of normal activity. Acquired coagulopathies generally are characterized by multiple coagulation factor deficiencies. The effect was studied of such combined deficiencies on the PT/APTT using plasma from patients congenitally deficient in specific factors and pooled normal plasma. The PT begins to lengthen when individual factor levels fall below 25%. The APTT becomes prolonged when the levels of Factor V fall below 45%; the levels of Factors II and XI fall below 40%; and the levels of Factors I, V, VII, VIII, IX, and XII fall below 25% of normal. When plasma samples containing 50% activity of a single factor and 100% of all other factors were prepared by mixing the congenitally deficient plasma samples with the normal pool, the resulting mixtures had normal PT and APTT values. However, when two of these 50% factor-deficient plasmas were combined so that the mixture contained 75% activity of two coagulation factors and 100% of all other factors, the resulting PT and APTT were prolonged over the clotting times of either 50% factor-deficient plasma. Similar findings were obtained in patients with mild factor reductions caused by warfarin treatment. These data indicate that prolongations of the PT and APTT in disorders of coagulation affecting multiple factors represent less of a reduction in factor levels than is generally appreciated. This may explain the poor clinical correlation between abnormalities in these test results and clinical bleeding in acquired disorders of hemostasis.

Blood Coagulation 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↗
PubMed1982

The effects of inaccurate blood sample volume on prothrombin time (PT) and activated partial thromboplastin time (aPTT).

The results of determinations of the prothrombin time (PT) and the activated partial thromboplastin time (aPTT) are frequently used to assess hemostatic function. Accurate results for these laboratory tests depend on many variables, one of which is the ratio of plasma to anticoagulant. We studied 12 patients and 4 normal subjects to determine the effects of sample volume on PT and aPTT. We conclude that underfilling may produce profound effects, particularly on the aPTT. In contrast, overfilling rarely affects the results. The greatest effects of sample volume were observed in specimens in which the true PT or aPTT was elevated. A normal PT or aPTT result on any specimen, regardless of sample volume, strongly suggests that the true value is normal.

Adult↗
PubMedDate not supplied

Variations in prothrombin time and international normalized ratio over 24 hours in warfarin-treated patients.

STUDY OBJECTIVE: To determine the variation of prothrombin times and international normalized ratio (INR) over 24 hours in humans. DESIGN: Prospective, parallel study. SETTING: University-affiliated general clinical research center. PATIENTS: Six patients receiving long-term warfarin therapy and six sex-matched controls. INTERVENTIONS: Warfarin was administered to the patients at 6:00 P.M. MEASUREMENTS AND MAIN RESULTS: Prothrombin times and INR were determined every 2 hours over 24 hours. Time of study entry, meals, and sleep cycles were controlled. A significant cosinor rhythm for prothrombin times and INR (p < or = 0.03) occurred in warfarin-treated patients, suggesting that diurnal variation occurs. The mean difference between the peak and trough prothrombin times was 1.8 +/- 0.9 seconds (range 0.8-3 sec) with a mean change of 9.3% +/- 3.7%. The peak prothrombin time and INR values occurred between 4:00 A.M. and 8:00 A.M. in five patients, and trough values between 6:00 P.M. and midnight in five. No significant cosinor rhythm was noted for controls (p > 0.5). CONCLUSION: Significant variations in prothrombin time and INR occurred in patients receiving warfarin therapy, with the highest values occurring in the morning and the lowest in the evening. These results may have clinical implications for patients receiving either high- or low-intensity warfarin therapy.

Adult↗
PubMed1995

Evaluation of a commercially available prothrombin time assay kit for use in dogs and cats.

A commercially available assay kit provided a rapid, inexpensive means of evaluating prothrombin time, requiring only 1 drop of fresh blood. We evaluated the assay kit for its ability to accurately measure prothrombin time in dogs and cats, comparing it with a validated prothrombin time assay performed in laboratories. Prothrombin times determined by validated laboratory and assay kit methods were compared, using simple regression analysis. Correlations were high (canine study, r2 = 0.96; feline study, r2 = 0.90; P = 0.0001 in both studies). We concluded that the assay kit compared favorably with the validated laboratory technique. The simplicity and speed with which the test can be performed, accuracy of results, small blood volume required, and cost-effectiveness make the assay kit well suited for prothrombin time measurement by small animal practitioners.

Animals↗
PubMedDate not supplied

Simplified calibration of prothrombin time assays.

The calibration of prothrombin time (PT) assays was studied. A simple calibration between pooled normal plasma and pooled stable plasma was as satisfactory as more complex calibration methods based on linear or orthogonal regression between log clotting times of abnormal and/or normal plasmas.

Blood Coagulation↗
PubMed2005

Prolonged prothrombin time, Factor VII and activated FVII levels in chronic liver disease are partly dependent on Factor VII gene polymorphisms.

BACKGROUND: Prothrombin time is a benchmark for functional assessment in cirrhosis and Factor VII levels (FVII), crucial in determining the prothrombin time, are genetically determined. METHODS: We have evaluated the prothrombin time, a number of haemostatic variables synthesised by the liver (FII, FV, FVII and activated FVII, AT and fibrinogen) and two polymorphisms of the FVII gene (5'F7 and 353R/Q) in: (a) patients with liver cirrhosis (n=118), (b) patients with chronic hepatitis (n=102) and (c) controls (n=100). RESULTS: By one-way analyses of variance, the prothrombin time and the mean levels of the FII, FV, FVIIc, FVIIa, and AT were statistically different between cirrhotics, chronic hepatitis patients and controls. The allele frequency of the FVII polymorphisms did not differ between the three groups. Those rare patients (4.6%) who were homozygous for the type 2 alleles had markedly reduced FVIIc and FVIIa levels. The analysis carried out taking into account Child class versus FVII genotype showed that the mean FVIIc levels were comparable for different genotypes within each Child's class, with the exception of the patients homozygous for the type 1 allele. CONCLUSION: Our findings help to explain the not infrequent finding of a severely prolonged prothrombin time in patients who are otherwise in a good functional class.

Alleles↗
PubMed1999

The effects of freeze drying and freeze drying additives on the prothrombin time and the international sensitivity index.

AIM: To determine whether freezing, freeze drying protective additives, or freeze drying of plasma samples from patients on coumarin treatment and from normal individuals affects prothrombin times or the international sensitivity index (ISI) calibration. METHODS: The effect of the addition of the protective additives singly and combined on the prothrombin time of coumarin samples and normal samples before and after freeze drying was observed using high and low ISI reference thromboplastins. ISI values were also determined. RESULTS: Freezing caused a prolongation of prothrombin time in the normal plasma samples with both reagents, which was significant with the low ISI human. Prolongation (non-significant) of the prothrombin time in coumarin plasma samples occurred with the human reagent only. Significant prolongation of normal prothrombin time by some of the protective additives before and after freeze drying was observed with both thromboplastins but to a greater extent with the human. Significant prolongation of prothrombin time in coumarin plasma samples was observed, but again was more marked with human thromboplastin. An approximate ISI was determined on the 20 coumarin samples. The only marked ISI change was with the WHO human thromboplastin after freeze drying of plasma, where a decrease from 0.95 to 0.90 was observed, corresponding to a marked prothrombin ratio increase. CONCLUSIONS: Freeze drying additives and the freeze drying procedure prolong normal and coumarin prothrombin times, with low ISI thromboplastin. Less marked prolongations occurred with a high ISI rabbit reagent, coumarin samples showing more significant prolongations. Marked ISI change in freeze dried plasma was only recorded with the low ISI ECAA human reagent. Frozen normal plasma samples cannot be used with confidence for ISI calibrations.

Animals↗
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↗
PubMedDate not supplied

Simplified prothrombin time standardization.

An analysis of prothrombin time (PT) standardization methods is presented. The present recommended ratio method demonstrated complex calibration and wide therapeutic ranges. Standardization by coagulation activities resulted in different therapeutic ranges due to the different sensitivity of assays for the protein induced by vitamin K absence (Pivka) inhibitor. A new method--the modified coagulation activity method--applied a reference assay against which any PT assay can be calibrated by clotting times, and the results were expressed in coagulation activities by the reference assay. This method was preferable due to simple calibration, narrow therapeutic ranges and identical results by any PT assay.

Blood Coagulation↗
PubMed1993

Standardization of prothrombin times in newborn infants.

The prothrombin time (PT) for patients receiving warfarin varies widely, reflecting the heterogeneity of thromboplastin reagents. The International Committee on Thrombosis and Haemostasis recommends that PT values for these patients be expressed as international normalized ratios. This study showed that thromboplastin reagents also significantly influence PT values in neonatal plasma and that expressing PT values as international normalized ratios decreases this variability.

Adult↗
PubMed1996

Influence of sample predilution on the sensitivity of prothrombin time in feline plasma.

The prothrombin time (PT) is measured in feline plasma usually by means of a method that has been optimized for measurements in human plasma (standard test). In the present study the sensitivity of this test was investigated in comparison to a modified PT using a human placental thromboplastin. In the modified test, 100 microliter sample predilution (1:5, 1:10, and 1:20) were incubated with 100 microliter of a human fibrinogen solution (2 g/l) until 100 microliter Ca-thromboplastin was added. When measured in 31 samples with a reduced, and 22 samples with an increased activity of the coagulation factors II, V, VII and/or X the modified test showed an increased sensitivity as well as a correlation between PT and the changes in single factor activity which was distinctly closer compared to the standard test. The highest sensitivity was produced by a 1:10 or 1:20 sample dilution. A test procedure modified in this way, is thus, a more reliable screening test for the extrinsic system in cats and should be used for routine diagnostics.

Animals↗
PubMed2000

A comparison of two sodium citrate concentrations in two evacuated blood collection systems for prothrombin time and ISI determination.

The prothrombin time is usually measured in citrated plasma. The W.H.O. recommended concentration of sodium citrate for blood collection for laboratory control of oral anticoagulant therapy is 0.109 M. Some evacuated blood collection systems include 0.105 M sodium citrate. The purpose of the present study was to establish the difference in ISI calibration between 0.109 and 0.105 M citrate, using 7 types of thromboplastin and various types of instrumentation. The two citrate concentrations were provided in both evacuated siliconised glass tubes and in evacuated polyethylene terephtalate (PET) tubes. The ISI difference between the two citrate concentrations was 5.4% for one system but not greater than 3% for all other systems when blood samples were collected with either siliconized glass or PET tubes. Most of the ISI differences between the two citrate concentrations were not significant at the 5% level. It is concluded that the ISI differences between 0.105 M and 0.109 M citrate are not of practical importance. In contrast, ISI differences between siliconised glass and PET tubes, using either 0.105 or 0.109 M citrate, were significant (p <0.05) for most thromboplastin systems and amounted to 7%. ISI interchange between these glass and PET tubes could induce INR differences amounting to 14%, which could affect clinical dosage of oral anticoagulants.

Blood Specimen Collection↗
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↗
PubMed1981

Alterations of prothrombin time and activated partial thromboplastin time in dogs with hepatic disease.

Reference intervals for prothrombin time (PT) and activated partial thromboplastin time (APPT) of undiluted and serial dilutions of citrated platelet-poor plasma were determined for 30 healthy dogs. The PT and APTT were similarly determined for 32 dogs with naturally occurring hepatic disease. Hepatic disease was confirmed by histopathologic examination of hepatic biopsy materials and comprised degeneration (13 dogs), inflammation (11 dogs), cirrhosis (4 dogs), and neoplasia (4 dogs). Coagulation test values were compared with serum alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transpeptidase activities and Bromsulphalein retention for sensitivity in detecting hepatic disease in the dog. Coagulation test results were at variance with reference values in 66% of the 32 dogs with hepatic disease; serum alanine aminotransferase, alkaline phosphatase, and gamma-glutamyl transpeptidase were increased in 59%, 72%, and 75%, respectively and Bromsulphalein retention was increased in 22% of the 32 dogs. Thus, the PT and APTT were sensitive indicators of hepatic disease. However, the PT and APTT lacked specificity for any given hepatic disease. The sensitivity of the coagulation tests for detecting hepatic disease was enhanced by using dilutions of citrated platelet-poor plasma. Only 15% of dogs with hepatic disease showed variances from reference values in the coagulation tests done with undiluted plasma, but 66% showed variances in the tests with dilutions of plasma. Coagulation tests were also done in 13 dogs with normal hepatic function amd morphology, but with various extrahepatic diseases: chronic renal disease (5 dogs), dirofilariasis (4 dogs), encephalitis (1 dog), cutaneous disease (2 dogs), and femoral fracture (1 dog). Twelve of the 13 dogs had coagulation test values within the reference intervals.

Animals↗