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PubMed2004

Can we rely on arterial line sampling in performing activated plasma thromboplastin time after cardiac surgery?

BACKGROUND AND OBJECTIVE: Arterial catheters are routinely used to sample blood for clotting studies in most cardiothoracic intensive care units. The clotting profile in surgical bleeding after cardiac surgery influences further management. Aspiration and discard of a certain amount of blood from the line, prior to sampling, are assumed to clear heparin contamination. We have investigated this assumption through analysis of the clotting profile by simultaneous arterial line and peripheral venous samples. METHODS: The morning following cardiac surgery, simultaneous arterial line and peripheral venous blood samples were taken for activated plasma thromboplastin time (APTT) ratio and international normalized ratio (INR) in 49 randomly selected patients. Also, a thromboelastogram analysis (TEG) (n = 7) was made. A survey of 22 UK cardiothoracic intensive care units was carried out to determine the practice for the withdrawal of blood for clotting studies. RESULTS: The median arterial APTT ratio value was 1.32 +/- 0.52 as compared to the median peripheral APTT ratio value which was 1.1 +/- 0.24 (P < 0.001). INR values were statistically similar by both routes. Heparin contamination was confirmed by TEG which revealed that the R-value for arterial catheter blood samples without heparinase in the cup was higher (406.00 +/- 64.44 s) compared with the value for arterial samples with heparinase in the cup (318.28 +/- 47.26s, P < 0.05). The survey of 22 UK cardiothoracic intensive care units showed that heparinized arterial lines were by far the commonest ports used for blood withdrawal for the measurement of APTT ratio results. CONCLUSIONS: Samples withdrawn from heparinized arterial lines cannot be relied upon for APTT ratio results.

Blood Coagulation Tests↗
PubMed1980

Circular dichroic, infrared and other studies on the protein component of pig brain thromboplastin.

1. A four-step procedure used to isolate the protein component (apoprotein III) of pig brain thromboplastin yielded approximately 25 mg from 500g of brain. 2. In the absence of detergent, apoprotein III had an apparent mol.wt. of 360 000 by gel-filtration, and, after electrophoresis on polyacrylamide gels in the presence of sodium docecyl sulphate, it appeared as a major protein band of mol.wt.59 000, suggesting the existence of polymeric and monomeric forms. 3. Chemical analyses of apoprotein III revealed that hydrophilic and hydrophobic amino acids were present in a ratio of 3:2, together with approx, 9% (w/w) of carbohydrate. 4. The far-u.v.c.d. and i.r. spectral data indicated that, like other membrane proteins, apoprotein III has a high percentage of unordered structure with lesser amounts of alpha and beta-forms. 5. Relipidation of apoprotein III to restore clotting activity caused no extensive alteration in the c.d. and i.r. spectra, indicating that the phospholipid associates with a comparatively small hydrophobic segment. The constrained unordered conformation, which makes the major contribution to the c.d. spectrum, probably forms a separate domain in the aqueous phase. The absence of any increase in the amplitude of both negative c.d. extrema, following relipidation, contrasted with the substantial increase observed in a helix-forming solvent and raises the possibility that the more stable polymeric form of apoprotein III is retained as the active form in the lipid phase. 6. We suggest that as a consequence of cell membrane damage, the recognition and activation of factor VII may involve minor changes of conformation that are dependent upon the flexibility inherent in an unordered secondary structure.

Amino Acids↗
PubMed1999

The effect of sample size on fresh plasma thromboplastin ISI determination.

The possibility of reduction of numbers of fresh coumarin and normal plasmas has been studied in a multicentre manual prothrombin (PT) calibration of high international sensitivity index (ISI) rabbit and low ISI human reference thromboplastins at 14 laboratories. The number of calibrant plasmas was reduced progressively by a computer program which generated random numbers to provide 1000 different selections for each reduced sample at each participant laboratory. Results were compared with those of the full set of 20 normal and 60 coumarin plasma calibrations. With the human reagent, 20 coumarins and seven normals still achieved the W.H.O. precision limit (3% CV of the slope), but with the rabbit reagent reduction < 50 coumarins with 17 normal plasmas led to unacceptable CV. Little reduction of numbers from the full set of 80 fresh plasmas appears advisable. For maximum confidence, when calibrating the ISI of a new reagent, it would always seem worthwhile to use the full number of patients' and normal plasmas at each centre for the initial calibration, i.e. 60 fresh coumarin and 20 fresh normal plasmas. Smaller numbers should achieve the required precision with the lower ISI reagent.

Animals↗
PubMed2001

Increased incidence of venous thrombosis in patients with shortened activated partial thromboplastin times and low ratios for activated protein C resistance.

A cohort of 69 hospital patients with shortened activated partial thromboplastin time (APTT) were prospectively identified and were further investigated for resistance to activated protein C (APC). This was quantified by APTT-based and Russel viper venom time (RVVT)-based methods. The prevalence of objectively confirmed venous thromboembolism (VTE) in this cohort was 19% (13/69). Of these 69 patients, 28 also had low APC resistance ratios and the incidence of VTE among these patients (group 1) was 36% (10/28). This was significantly higher (P=0.003) than that in the remaining 41 patients (group 2) with shortened APTT and normal APC resistance (7%, 3/41). DNA analysis confirmed 13 of the group 1 patients were FV Leiden positive. The incidence of VTE in the FV Leiden group (group 1a, n=13) was 38% (5/13) and in the group whose abnormal resistance to APC was independent of FV Leiden (group 1b, n=15) was 33% (5/15). These results suggest that a shortened APTT, coexisting with a low APC resistance ratio, regardless of FV Leiden carriership status, is a marker for VTE. Increased resistance to the anticoagulant activity of APC is multifactorial as reflected by evidence of abnormal resistance differing in the two assays.

Activated Protein C Resistance↗
PubMed2000

Influence of factor VIII:C and factor IX activity in plasmas of haemophilic dogs on the activated partial thromboplastin time measured with two commercial reagents.

The present study is based on 145 plasma samples with a reduced activity of factor VIII:C (range: 0.009-0.62 IU mL-1) and 28 samples with a reduced factor IX activity (range: 0.035-0.55 IU mL-1). The samples were collected from dogs with haemophilia A (n=22) or haemophilia B (n=3), some of these during substitution therapy. For all samples the activated partial thromboplastin time (APTT) was measured with two commercial reagents containing kaolin as a contact activator. In each case, the deficiency of factor VIII:C or IX was reflected in abnormal results of the APTT. This was true for both reagents. A significant correlation (P < 0.001) was found between factor VIII:C activity and APTT (reagent 1, Pathromtin(R); Spearman's rank correlation coefficient, rS=-0.731, reagent 2, PTT-Reagenz; rS=-0.875) as well as between factor IX activity and APTT (reagent 1, rS=-0.819; reagent 2, rS=-0.955]. In each case, the relationship between coagulation factor activity and APTT could be proven most precisely by geometric regression. The results of this study illustrate the applicability of commercial APTT test kits as a sensitive screening test of factor VIII:C and IX deficiencies in canine plasma.

Animals↗
PubMed2003

Heparin monitoring in sheep by activated partial thromboplastin time.

Heparin anticoagulation is utilized during and after vascular surgery in animals to reduce the risk of acute or chronic thromboembolic problems. In this study, we examined variation of activated partial thromboplastin time APTT) after the intravenous bolus IV bolus) and subcutaneous SC) heparin injection in order to monitor heparin therapy in sheep. Nine healthy sheep were assigned to 3 groups A, B, and C) according to their body weights: less than 40 kg, 40 to 80 kg, and more than 80 kg, respectively. All animals were treated with heparin 300 IU/kg body weight) through two routes, and the APTT, fibrinogen, and platelet count were measured before and every hour after treatment. This showed that the APTT was increased significantly between 1 to 4 hours after IV bolus injection and between 2 to 6 hours after SC injection P < 0.05). The APTT was returned to baseline values 6 and 10 hours after the respective treatments. The APTT in Group C was consistently higher than in Group A and B after heparin treatment by the two routes. The APTT ratio entered the subtherapeutic range 5 and 8 hours after IV bolus and SC injection, respectively. The APTT ratio was maintained in the therapeutic range for about 1 and 4 hours after IV bolus and SC injection, respectively. The highest APTT ratio in Group C after SC injection of heparin was significantly higher than that in Groups A and B P < 0.05). The mean platelet counts in Groups A, B, and C before the injection were 3197 +/- 365.6, 2886 +/- 78.2, and 1861 +/- 298.0 102/microL, respectively. The mean platelet count gradually decreased without significant variation after IV bolus and SC injection. These results produced elementary data for monitoring in sheep using APTT, and suggested that heparin should be administrated by the SC route at 4-hour intervals in order to remain in the therapeutic range, after an initial IV bolus dose.

Animals↗
PubMed1999

Variability of prothrombin time and activated partial thromboplastin time in the diagnosis of increased surgical bleeding.

BACKGROUND: Prothrombin time (PT) and activated partial thromboplastin time (APTT) are used to diagnose causes of increased surgical bleeding and to guide treatment of acquired coagulation factor deficiency. This study compared the sensitivity of various commercial PT and APTT tests in patients with dilutional coagulopathy. STUDY DESIGN AND METHODS: A prospective study was used to identify patients who experienced increased surgical bleeding during elective extensive (>10 spinal segments) spinal fusion and instrumentation. In patients with clinical signs of increased bleeding, blood was obtained to compare the sensitivity of various commercial PT and APTT tests. PT, PT ratio, the International Normalized Ratio (INR), APTT, and APTT ratio were compared for their sensitivity in the diagnosis of a dilutional coagulopathy. RESULTS: Sixteen patients experienced increased bleeding during surgery. Mean estimated blood volume lost exceeded 1 blood volume (1.14 +/- 0.28). PT and APTT test results varied markedly. In the most sensitive PT and APTT tests, the results were 1.5 times the mean reference range values in all but on of the patients. The least sensitive combination of tests had results that were 1.5 times the mean reference range values in only 2 of 16 patients. Variability among tests was not reduced by the use of the PT or the APTT ratio, by the use of INR, or by incorporation of a measure of PT or APTT test sensitivity to factor-deficient serum. CONCLUSION: In surgical patients with dilutional coagulopathy, diagnostic and treatment decisions could depend on which PT and APTT test was used to determine the etiology of increased bleeding. This study indicates that the relationship between increased bleeding and an increased PT and APTT may be more difficult to define than is suggested by current practice guidelines. Each laboratory must establish guidelines based on reagent and instrument sensitivity to coagulation factor dilution.

Blood Coagulation Disorders↗
PubMed2005

An in vitro study comparing the effects of Hextend, Hespan, normal saline, and lactated ringer's solution on thrombelastography and the activated partial thromboplastin time.

OBJECTIVE: The purpose of this study was to determine if 6% HES 450/0.7 (hydroxyethyl starch 450/0.7) in normal saline (Hespan) and 6% HES 450/0.7 in lactated Ringer's solution (Hextend) have the same inhibition of the intrinsic coagulation pathway and platelet function. Multiple studies have suggested that 6% Hespan inhibits coagulation and increases chest tube drainage and transfusion requirements in cardiac surgical patients. There have been few studies of the effects of 6% Hextend, a relatively new plasma volume expander, on coagulation and the results thus far have been mixed. DESIGN: A prospective in vitro study. SETTING: A large academic medical center. PARTICIPANTS: Blood was collected from 30 healthy volunteers. Interventions : The blood was fractionated and diluted by 30% with Hextend, Hespan, normal saline, and lactated Ringer's solutions, with a native sample for a control. MEASUREMENTS AND MAIN RESULTS: Primary outcome measures were thromboelastography and activated partial thromboplastin time (APTT). For each of the TEG parameters, there was no difference between samples diluted with Hextend compared with Hespan (p > or = 0.112 in all cases). APTT did not differ significantly between samples diluted with Hextend compared with Hespan (p = 0.562). CONCLUSIONS: This prospective in vitro study suggests that Hextend and Hespan, hydroxyethyl starch 450/0.7 in different base solutions, exhibit the same effect on platelet function as measured by the TEG.

Adult↗
PubMed1999

Effects of haemolysis, lipaemia and bilirubinaemia on prothrombin time, activated partial thromboplastin time and thrombin time in plasma samples from healthy dogs.

Interferences caused by haemolysis, lipaemia and bilirubinaemia on prothrombin time (PT), activated partial thromboplastin time (APTT) and thrombin time (TT in normal canine plasma samples were studied using commercially available reagents and a steel ball coagulometer. Haemolysis significantly interfered with APTT (P = 0.0076) and TT (P = 0.0292). Regression analysis showed that TT was significantly shortened as haemoglobin concentrations increased. Lipaemia increased as demonstrated by regression analysis. Bilirubin significantly interfered with PT (P=0.0003) and APTT (P=0.002). Although statistically significant, none of the differences found were of clinical relevance.

Animals↗
PubMed2000

Superiority of enoxaparin versus unfractionated heparin for unstable angina/non-Q-wave myocardial infarction regardless of activated partial thromboplastin time.

BACKGROUND: Whether the clinical superiority of enoxaparin versus unfractionated heparin (UFH) depends on a more stable antithrombotic effect or the proportion of patients not reaching the therapeutic level with UFH has not been addressed. METHODS: All patients participating in the Thrombolysis In Myocardial Infarction 11B trial who received UFH and had sufficient activated partial thromboplastin time (aPTT) data (n = 1893) were compared with patients who received enoxaparin (n = 1938). Patients receiving UFH were divided into 3 categories depending on mean aPTT values throughout 48 hours: subtherapeutic, for those in whom the average aPTT fell below 55 seconds; therapeutic, between 55 and 85 seconds; and supratherapeutic, longer than 85 seconds. Events and bleeding rates were determined at 48 hours. RESULTS: A small portion of patients (6. 7%) had a subtherapeutic average aPTT value (n = 127). Forty-seven percent of patients (n = 891) fell within the therapeutic range, and 46% were in the supratherapeutic level (n = 875). Event rates were 7. 0% in the UFH group versus 5.4% with enoxaparin (P =.039). Events rates were higher in every aPTT strata compared with enoxaparin and statistically significant in the supratherapeutic group (odds ratio 0.65; 95% confidence interval, 0.47-0.89). Major bleeding rates were 0%, 0.6%, and 0.9% for the subtherapeutic, target, and supratherapeutic strata, respectively, and 0.8% with enoxaparin. Minor hemorrhages occurred in 5.1% of patients receiving enoxaparin versus 3.9%, 2%, and 2.3%, respectively, for the UFH subgroups (P <. 001 for all UFH groups vs enoxaparin). CONCLUSIONS: Enoxaparin showed a better clinical profile compared with every level of anticoagulation with UFH. Potential mechanisms for enoxaparin superiority are stable antithrombotic activity, lack of rebound thrombosis, and intrinsic superiority.

Aged↗
PubMed1997

Single or duplicate analysis for automated prothrombin time and activated partial thromboplastin time?

The introduction of automated coagulation analysers raises the possibility of performing routine coagulation tests as single rather than duplicate analyses. This study compares the duplicate results of the prothrombin time (PT) and activated partial thromboplastin time (aPTT) to that of a single result obtained by the MLA Electra 1000c using two different methods. The first method looks specifically at the difference between the mean duplicate result and the single result to determine if they alter patient management. This method found that two of 4152 PTs (0.048%) and two of 3047 aPTTs (0.065%) were clinically significant. The second method statistically assessed the agreement between the traditional mean duplicate result and the single test. This supported the introduction of single testing as the calculated 95% confidence intervals demonstrate that each result is interchangeable for purposes of clinical interpretation. These results supported the introduction of single testing for PT and aPTT estimation in our laboratory. The introduction of single testing was accompanied by changes to quality control and machine maintenance to ensure that the functions previously covered by duplicate testing were maintained. A strict protocol for repeat testing has also been adopted.

Australia↗
PubMed2003

Subjects with a shortened activated partial thromboplastin time show increased in-hospital mortality associated with elevated D-dimer, C-reactive protein and glucose levels.

BACKGROUND: Shortened activated partial thromboplastin time (aPTT) values are associated with enhanced coagulation activation. However, the clinical relevance of shortened aPTTs is not well defined. The aim of this study was to determine the in-hospital mortality rate in subjects with shortened aPTTs and the effects of polymorphism in plasminogen activator inhibitor (PAI)-, t-PA- and factor XIII gene on the coagulation status. D-dimer, C-reactive protein (CRP) and glucose, markers that have been related with increased mortality, were tested. RESULTS: We found that a shortened aPTT on admission was associated with an increased risk of in-hospital mortality (OR=2.6, 95% CI: 2.1-3.5). Non-survivors with short aPTTs had significantly higher plasma D-dimer, CRP and glucose levels compared with survivors. Subjects homozygous for PAI-1 5G and t-PA I alleles showed higher plasma D-dimer levels compared with 4G/4G PAI-1 (p=0.02) and D/D t-PA (p=0.001) homozygotes, respectively. CONCLUSIONS: These results suggest that PAI-1 4G/5G and t-PA I/D polymorphisms determine plasma D-dimer levels in patients with shortened aPTT values. Preliminary results show that, among patients with short aPTTs, homozygosity for the hyperfibrinolytic PAI-1 5G or tPA I alleles are at increased risk of in-hospital mortality compared with 4G/4G PAI-1 and D/D tPA homozygotes (OR=2.6, 95% CI: 1.3-5.5 and OR=5.5, 95% CI: 1.3-24.5, respectively).

Antithrombin III↗
PubMed2005

Effects of platelets and platelet-derived material on the activated partial thromboplastin time (Cephotest) coagulation test.

OBJECTIVE: The Cephotest is an activated partial thromboplastin time (APTT) test used to measure the activity of the intrinsic pathway of coagulation. To perform this test, blood is usually centrifuged to obtain plasma that is almost without erythrocytes and leucocytes and with only a minimal amount of platelets. MATERIAL AND METHODS: In the present experiments blood was centrifuged at different speeds to produce either platelet-poor plasma (PPP) or platelet-rich plasma (PRP). PPP and PRP obtained from the same whole blood samples from each of several persons were tested in pairs using the standard Cephotest reagent to observe the consequences of Cephotest being performed on plasma containing platelets. The same procedure was used with a Cephotest reagent with a reduced concentration of phosphatidylserine. In succeeding experiments the PRP was preincubated with SFLLRN or Ca-ionophore to activate the platelets, a procedure also known to produce platelet-derived microparticles. PPP and PRP were compared by thrombin time and reptilase time tests to find out at which stage platelets might influence the Cephotest. RESULTS: The results showed that the platelets did influence Cephotest when using both the regular reagent and the phospholipid-reduced agent. When using the regular reagent, PRP showed a tendency towards a longer APTT than PPP. It is suggested that this was caused by platelets consuming some of the first traces of thrombin generated. CONCLUSIONS: When using the phospholipid-reduced reagent, PRP showed a shorter APTT than PPP, probably because the platelets contributed phosphatidylserine to the system. When the platelets were activated before testing, their effects on the tests were increased. Microparticles that formed during platelet activation may have contributed to these effects.

Blood Coagulation↗
PubMed2002

Transient lupus anticoagulant and prolonged activated partial thromboplastin time secondary to Epstein-Barr virus infection.

We describe the case of a previously well 19-month-old boy who presented with an acute Epstein-Barr virus infection and a prolonged activated partial thromboplastin time (APTT) associated with the presence of a transient lupus anticoagulant (LA). The boy had an excellent outcome, with gradual normalization of the APTT and disappearance of the LA.

Epstein-Barr Virus Infections↗
PubMed1993

Artifactual prolongation of the activated partial thromboplastin time mimicking a coagulopathy. A lesson relearned.

A markedly prolonged activated partial thromboplastin time (APTT) was observed in a 61-year-old woman with bruising and a decreasing hematocrit. Coagulation laboratory evaluation was sought to determine the cause of the prolonged APTT and bleeding. Evaluation demonstrated that, rather than identifying a coagulopathy, the APTT prolongation was most likely artifactual. The APTT was actually very short. With a combination of a relatively strong activating APTT reagent (Dade Actin; Dade, Miami, FL) and a fixed lag phase in the automated coagulation instrument (16 seconds), the clot formed before the instrument began to read. Thus, during the period of observation (120 seconds), no change in optical density was observed. This was interpreted by the laboratory as "> 120 seconds." This case reminds those involved in the performance and interpretation of APTTs of the importance of a manual or visual method of verifying markedly prolonged APTTs.

Artifacts↗
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↗
PubMed1993

Behavior of diluted activated partial thromboplastin time in pregnant women with a lupus anticoagulant.

The present study was developed to verify whether a reduction in phospholipid concentration could increase the activated partial thromboplastin time (APTT) sensitivity to detect lupus anticoagulant (LA) during pregnancy. The authors studied 38 pregnant women (10 normal subjects and 28 patients with associated clinical complications) and 40 nonpregnant control subjects. Tests to detect LA, including APTT, platelet neutralization procedure (standard APTT), the kaolin clotting time, the diluted Russell viper venom test neutralized by lysed platelets, and factor assays, were performed. Positive results were found in 5 of 28 pregnant women with associated clinical complications. The APTT, using three different phospholipid concentrations (standard and more diluted cephalin), was performed on plasma samples and on its 1:1 mixture with normal plasma. The behavior of standard and diluted APTT was similar in negative LA pregnant women and nonpregnant control subjects. The mean values showed nonsignificant differences. Four of five pregnant women with positive LA findings had a prolonged APTT, which was not corrected by the addition of normal plasma using standard conditions. When diluted phospholipids were used, only one of them had a prolonged APTT that was corrected by the addition of normal plasma. Therefore, the highest sensitivity (80%) and specificity (100%) of the APTT to detect LA in pregnant women were obtained using the standard conditions.

Female↗
PubMed1993

ARACHnase. An evaluation of a positive control for platelet neutralization procedure testing with seven commercial activated partial thromboplastin time reagents.

ARACHnase (Hemostasis Diagnostics International Co., Denver, CO) is a normal plasma that contains a venom extract from the brown recluse spider, Loxosceles reclusa, which mimics the presence of a lupus anticoagulant (LA). Seven activated partial thromboplastin time (APTT) reagents were used for platelet neutralization procedure (PNP) testing with ARACHnase: Automated APTT (Organon-Teknika, Durham, NC); Thrombofax and Thrombosil (Ortho, Raritan, NJ); Actin and Actin FSL (Dade, Aguado, PR); and Thromboscreen-Kontact and Thromboscreen-APTT LS (Pacific-Hemostasis, Ventura, CA). ARACHnase consistently displayed a positive PNP result of greater than 5 seconds correction of the initial baseline APTT. Thus, ARACHnase may provide a positive control for LA testing, regardless of the choice of APTT reagent and activator/phospholipid combination.

Adult↗