Activated Partial Thromboplastin Time Test Research Articles

Lactobacillus casei modulates the inflammation-coagulation interaction in a pneumococcal pneumonia experimental model

BackgroundWe have previously demonstrated that Lactobacillus casei CRL 431 administration improved the resistance to pneumococcal infection in a mouse model.MethodsThis study examined the effects of the oral administration of Lactobacillus casei CRL 431 (L. casei) on the activation of coagulation and fibrinolytic systems as well as their inhibitors during a Streptococcus pneumoniae infection in mice.ResultsThe alveolo-capillary membrane was damaged and the coagulation system was also activated by the infection. As a consequence, we could see fibrin(ogen) deposits in lung histological slices, increased levels of thrombin-antithrombin complex (TATc) in bronchoalveolar lavage (BAL) and plasma, decrease in prothrombin activity (PT) and prolonged activated partial thromboplastin time test (APTT) values. Factor VII (FVII) and factor X (FX) were decreased in plasma, whereas fibrinogen (F) and factor VIII (FVIII) were increased. The low levels of protein C (PC) in BAL and plasma proved damage on inhibitory activity. The infected animals showed reduced fibrinolytic activity, evidenced by an increase in plasminogen activation inhibitor-1 (PAI-1) in BAL and plasma. The pathogen induced an increase of TNF-α, IL-1β and IL-6 in BAL and serum a few hours after challenge followed by a significant decrease until the end of the assayed period. IL-4 and IL-10 in BAL and serum were also augmented, especially at the end of the experiment. The animals treated with L. casei showed an improvement of alveolo-capillary membrane, lower fibrin(ogen) deposits in lung and decrease in TATc. APTT test and PT, FVII and FX activity were normalized. L. casei group showed lower F levels than control during whole experiment. In the present study no effect of L. casei on the recovery of the inhibitory activity was detected. However, L. casei was effective in reducing PAI-1 levels in BAL and in increasing anti-inflammatory ILs concentration.ConclusionL. casei proved effective to regulate coagulation activation and fibrinolysis inhibition during infection, leading to a decrease in fibrin deposits in lung. This protective effect of L. casei would be mediated by the induction of higher levels of IL-4 and IL-10 which could regulate the anti-inflammatory, procoagulant and antifibrinolytic effects of TNF-α, IL-1β and IL-6.

Heparinoids algal and their anticoagulant, hemorrhagic activities and platelet aggregation

Polysaccharides extracted from brown marine algae represent a source of marine compounds with potential applications in medicine. Heparin-like compounds, fucoidans, have been proposed as alternatives to the anticoagulant heparin, which is prepared from mucous membrane of mammals. In this study, the activity of anticoagulant in activated partial thromboplastin time (APTT) and prothrombin time (PT) tests was assessed in the fucoidan (TF), from seaweed Fucus vesiculosus, partially desulfated fucoidans (PDF), desulfated fucoidans (DF) and purified fractions F1, F2 and F3 in acetone. Studies were also conducted to assess these polysaccharides for platelet aggregation and hemorrhagic activity. The APTT test showed high activity at 5 μg (≥240 s) for TF, F1 and F2 ( P < 0.001). PT test showed high anticoagulant activity at 50 μg (≥120 s) for F1 ( P < 0.001). Fraction F3, with low MW (15.2 kDa) and sulfate content (26.1%), had little effect in these two in vitro tests ( P < 0.001). These compounds demonstrated a two-phase response to platelet aggregation at 50 μg/mL. However, at a concentration of 0.1 mg/mL, a hypoaggregate profile was observed for all fractions tested ( P < 0.001). The analysis showed that fucoidans irreversibly induced platelet aggregation in high concentration. These polymers have low hemorrhagic effect when compared to heparin.

Activated Thromboplastin Time In Women With Recurrent Spontaneous Abortions

Haemostatic abnormalities have been associated with various complications of pregnancy. Information regarding haemostasis and recurrent abortion is scanty in Nigerian women. In this study, we aimed at assessing haemostasis in pregnant women with recurrent spontaneous abortions using the Activated Partial Thromboplastin Time (APTT). The APTT tests were performed on 23 pregnant women with prior history of recurrent abortions and, on two control groups comprising 50 healthy pregnant women and 50 non-pregnant women. The pregnant groups were all in second or third trimester of pregnancy. Six (24%) of the women with recurrent spontaneous abortions had shortened APTT ( 40 seconds) while 16 (64%) had normal values (30 – 40 seconds). Nine (18%) and 7 (14%) of the pregnant control had shortened and prolonged values respectively. One (2%) of the non- pregnant control had shortened APTT while 2 (4%) had prolonged APTT. There was a statistically significant difference between the mean APTT values of patients with recurrent spontaneous abortions and non- pregnant control (p = 0.0187). We conclude that the APTT in recurrent spontaneous abortions is not significantly different from that of normal pregnant women. However, it is abnormal when compared with non-pregnant women. Pregnant women with history of recurrent spontaneous abortions should therefore be routinely screened for haemostatic abnormalities. Keywords : APTT, Haemostasis Spontaneous recurrent abortions, Benin City Annals of Biomedical Science Vol. 2 (1) 2003: pp. 42-46

Evaluation of the REG1 Anticoagulant System Using Thrombelastography and Thrombin Generation Assay.

Background: The REG1 system (Regado Biosciences, Inc. Durham, NC) is a novel anticoagulant system which comprises RB006 (drug) and RB007 (antidote). The aptamer, RB006 selectively binds to FIXa and blocks factor Xa generation. RB007 is a complementary ligand that selectively binds to RB006, and reverses its anticoagulant effect (1). Phase 1 testing demonstrated a clear pharmacodynamic dose response to RB006 in plasma coagulation assays (1), but further work is needed to understand the pharmacodynamic response to the REG1 system in whole blood assays. Therefore, we evaluated the effects of RB006 and RB007 alone and in combination using activated partial thromboplastin time (APTT), viscoelastic (TEG®, Haemoscope, IL) and thrombin generation assay (Thrombinoscope™, Synapse BV).Methods: After IRB approval, blood samples were collected from 4 consented healthy volunteers into 3.2% citrate tubes. For APTT and TEG testing blood was placed in thirteen 2 ml Eppendorf tubes. Tube one had 20 μl of saline added and served as a control. The remaining 12 tubes were divided into 3 groups. Group1: RB006 (final concentrations 3, 6, 12, 18 and 24 μg/ml); Group 2: RB007 (final concentrations 6, 12, 24, and 48 μg/ml) and Group 3: combination of both agents at a weight:weight ratio 2 to 1 for RB007:RB006 (final concentrations as above). All testing was performed within 3-hour of blood draw. APTT was done using Hemochron Jr® (ITC, NJ) instrument in recalcified whole blood. TEG was peformed in recalcified whole blood, 360 μl activated with 2 nM thrombin. For Thrombinoscope, whole blood was centrifuged at 2000 x g for 15 min to obtain platelet poor plasma (PPP). PPP samples were prepared to contain the same concentrations of RB006, RB007, and combination of both agents as described in whole blood samples. Thrombin generation analyses were performed using microplate format using diluted Actin (Dade Behring, Marburg, Germany) as a trigger (2).Results: RB006 dose dependently increased APTT (Table 1). Increasing concentrations of RB006 progressively prolonged onset, and decreased the rate of thrombus formation on TEG (Figure1A). On Thrombinoscope, RB006 dose dependently delayed lag time and decreased peak thrombin generation (Table 1, Figure1B). All the parameters of aPTT, TEG and thrombin generation returned back to control values when combination of aptamer-anti-aptamer was tested. RB007 alone had no effects on any of the tests performed.Conclusion: Along with conventional point of care APTT testing TEG and Thrombinoscope methodologies can be very useful in monitoring the anticoagulation effects of aptamer, RB006, and its reversal with anti-aptamer, RB007.Effects of Aptamer, RB006, on aPTT and Thrombinoscope lag time/peak thrombinRB006μg/mlAPTT secLag time minPeak thrombin nM0 (control)51.3 ± 1.010.8 ± 0.3244 ± 16.2395.3 ± 3.014.2 ± 0.9173 ± 22.96152 ± 10.018.8 ± 0.5145 ± 23.012183 ± 4.324.1 ± 1.1105 ± 11.018238 ± 15.326.3 ± 2.392.3 ± 7.324257 ± 11.331.3 ± 3.888.2 ± 8.3Data shown as mean ± SD [Display omitted]

Measurement of prothrombin time (PT) and activated partial thromboplastin time (APTT) on canine citrated plasma samples following different storage conditions

Samples from 75 clinically ill dogs were utilised in the study. APTT and PT tests were performed immediately on fresh citrated plasma samples (Fresh). The remaining plasma was stored at −20 °C for less than 4 months ( n = 36 samples) or between 4 and 7 months ( n = 39 samples). In batches of five, frozen samples were thawed rapidly and APTT and PT tests were performed on the thawed samples immediately (0RT) and after storage at room temperature (23 °C, range: 22–25 °C) for 24 h (24RT) and 48 h (48RT). The median APTT value from the (0RT) samples was significantly longer than that obtained from fresh samples (15 s vs. 13.2 s) but the PT value was not statistically different (7.8 s vs. 7.6 s). The median APTT (15 s) and PT (7.5 s) results from the (24RT) samples were not statistically different to those from the (0RT) samples (APTT: 15 s, PT: 7.6 s) but both tests were significantly longer (APTT: 16.5 s, PT: 9.2 s) from the (48RT) samples. We concluded that long term batching and freezing of clinical samples at −20 °C is acceptable for measurement of PT but not of APTT. We demonstrated that APTT and PT results do not change following storage of samples at room temperature for 24 h but storage for 48 h may lead to statistically and clinically significant changes (values at least 25% higher than the high value of the laboratory’s reference interval) in both clotting times.

Preparation, characterization and anticoagulation of curcumin-eluting controlled biodegradable coating stents

Curcumin is pharmaceutically active in many ways, having properties including anticoagulation, anti-proliferation, anti-inflammatory, and may be used to fabricate drug-eluting stents to treat in-stent restenosis after stent implantation. Here we describe our investigations of curcumin-eluting PLGA coatings formed using the biodegradable polymer PLGA (polylactic acid-co-glycolic acid) as drug carrier and uniformly fabricated on the surface of 316L stainless steel stents by an ultrasonic spray method. Three doses were explored — low dose (∼ 140 μg per stent or 115 μg/cm 2), moderate dose (∼ 280 μg per stent or 230 μg/cm 2), and high dose (∼ 490 μg per stent or 408 μg/cm 2). Pre- and post-expansion morphologies of the stent coating were examined by optical microscopy (OM) and scanning electron microscopy (SEM), indicating that the coating not only was very smooth and uniform but also had the ability to withstand the compressive and tensile strains imparted without cracking from the stent during the expansion process. Atomic force microscopy (AFM) images indicated the topography of the PLGA-only and moderate dose curcumin-eluting stent that showed an average roughness below 1 nm; no drug particles could be seen on the stent surface, indicating that curcumin can be mixed with PLGA at the molecular level using an ultrasonic atomization spray method. The structure of the coating films was characterized by Fourier Transform Infrared (FTIR) spectroscopy and X-ray electron spectroscopy (XPS), with results suggesting that there was no chemical reaction between curcumin and the drug. The results of in vitro measurements of drug release from curcumin-eluting stents showed that all the curcumin-eluting stents studied exhibited a nearly linear sustained-release profile with no significant burst releases within the measurement period. The in vitro anticoagulation behavior of curcumin-eluting stents was investigated by static platelet adhesion and APTT (activated partial thromboplastin time) tests, revealing that the anticoagulation properties of curcumin-eluting stents are superior to those for stainless steel stents and PLGA-only-coated stents. The anticoagulation behavior of curcumin stents improved significantly as the drug dose was increased.

Stability of activated partial thromboplastin time (APTT) test under different storage conditions

We designed this study to assess the effect of storage time and temperature on the activated partial thromboplastin time (APTT) test and plasma activity of factor VIII (FVIII).A total of 71 subjects, comprising 34 healthy controls and 37 patients receiving unfractionated heparin were enrolled. After centrifugation of collected specimens aliquots of plasma were stored at room temperature (20–22°C), refrigerated at 2–6°C and frozen at − 40°C. Determination of APTT and plasma activity of FVIII were performed immediately after sampling (zero time) and after 6, 12 and 24 h. We found no significant difference in APTT after 6 h at room temperature and 4°C compared to zero time values (P > 0.05) in control group, while APTT was significantly changed at other storage conditions. With regard APTT test in patients on heparin therapy and samples for FVIII activity in healthy subjects; there was a statistically significant change in their results after 6, 12 and 24 h at room temperature, 4 and − 40°C compared to zero time value (P < 0.05). Our data demonstrate that the APTT test can be done within 6 h when stored at room temperature and 4°C without change in the result in healthy subjects. APTT test in patients on heparin therapy and samples for FVIII test in healthy subjects must be done immediately and without delay to avoid reduction in their activities.

Activated protein C resistance: The influence of ABO-blood group, gender and age

We have evaluated the potential influence of ABO-blood group, gender and age, on laboratory procedures used for detection of Activated Protein C Resistance (APCR), using over 300 normal donor samples and two distinct laboratory test procedures, one based on an Activated Partial Thromboplastin Time (APTT) and the other on a Russell Viper Venom Time (RVVT). We observed a statistically significant influence of ABO-blood group on APTT test times, both in the presence and absence of Activated Protein C (APC), which was no longer evident when using assay ratios. This ABO effect was not observed using the RVVT-based assay procedure. We also observed a gender effect on the APTT-based procedure, such that females (compared to males) provided shorter APTT test times (both with and without APC). This effect was still evident when using APTT assay ratios, but was again not observed using the RVVT-based procedure. We also observed an age related increase in APTT ratios. Interestingly, some previous studies have reported some specific gender and age related effects on APTT-based testing, but reports using RVVT-based testing are lacking, as are ABO related studies. Such findings should be considered as potential variables when associating specific laboratory based findings of APCR to clinical thrombophilia conditions.

The multiple faces of the partial thromboplastin time APTT

The multiple faces of the partial thromboplastin time APTT

Analysis of the Activated Partial Thromboplastin Time Test Using Mathematical Modeling

Activated partial thromboplastin time (APTT) is a laboratory test for the diagnosis of blood coagulation disorders. The test consists of two stages: The first one is the preincubation of a plasma sample with negatively charged materials (kaolin, ellagic acid etc.) to activate factors XII and XI; the second stage begins after the addition of calcium ions that triggers a chain of calcium-dependent enzymatic reactions resulting in fibrinogen clotting. Mathematical modeling was used for the analysis of the APTT test. The process of coagulation was described by a set of coupled differential equations that were solved by the numerical method. It was found that as little as 2.3×10 −9 μM of factor XIIa (1/10 000 of its plasma concentration) is enough to cause the complete activation of factor XII and prekallikrein (PK) during the first 20 s of the preincubation phase. By the end of this phase, kallikrein (K) is completely inhibited, residual activity of factor XIIa is 54%, and factor XI is activated by 26%. Once a clot is formed, factor II is activated by 4%, factor X by 5%, factor IX by 90%, and factor XI by 39%. Calculated clotting time using protein concentrations found in the blood of healthy people was 40.5 s. The most pronounced prolongation of APTT is caused by a decrease in factor X concentration.

Synthesis and Anticoagulant Properties of a Novel Heparinoid N-Sulfate-Bearing Vinylpolymer

A novel heparinoid polymer was prepared with an N-sulfate side chain group by sulfation of poly( N-vinylacetamide-co-vinylamine) [poly(NVA-co-VAm)] which was obtained by the partial hydrolysis of poly( N-vinylacetamide) [poly(NVA)]. The hydrolysis of poly(NVA) was controlled by reaction time and temperature and the sulfation of poly(NVA-co-VAm) was performed with chlorosulfonic acid. Poly( N-vinylacetamide-co-vinylamine-co-vinylsulfamic acid) [poly(NVA-co-VAm-co-VSA)] was confirmed by means of IR spectroscopy, and the degree of sulfation of poly(NVA-co-VAm-co-VSA) was estimated by elemental analysis. The anticoagulant properties of poly(NVA-co-VAm-co-VSA) were evaluated using the Lee-White clotting test and activated partial thromboplastin time (APTT) test. The human whole blood clotting time in the presence of poly(NVA-co-VAm-co-VSA) was prolonged compared with poly(NVA) and poly(NVA-co-VAm). The clotting time was prolonged with increased N-sulfate groups on the polymer. APTT tests of the polymer were also prolonged with N-sulfate increases. The results suggest that the N-sulfate components on the polymer can endow anticoagulant activity to synthetic polymers.

Stability of plasma for add-on PT and APTT tests.

We conducted studies to determine at what time point an add-on prothrombin time (PT) or activated partial thromboplastin time (APTT) test can be honored on specimens that have been received in the laboratory hours earlier without yielding results with clinically significant differences from those if the test had been performed on the original unstored plasma. PT and APTT tests were performed on blood samples from 20 healthy subjects, 30 patients receiving warfarin, and 30 patients receiving heparin anticoagulation therapy. The tests were performed on plasma prepared initially after the samples were obtained. The same tests were assayed on plasma that had been left on spun-down blood cells at room temperature for 2, 4, and 8 hours. We found that the PT of the majority of plasma samples from healthy subjects and from patients receiving oral anticoagulant therapy tended to become shorter on storage. However, the difference in PT values was small and had no clinical significance. In most cases, the APTT values for the stored plasma from healthy subjects tended to increase with time. Except in one specimen in which the 8-hour add-on APTT was 1.2 seconds longer than the APTT result for the original sample, all others had APTT results less than 1.2 seconds longer than the original values. In patients receiving heparin, the differences in APTT values between the initial and add-on tests were larger than those observed for healthy subjects. However, those differences are not beyond what we would accept for duplicate checks for heparinized samples with high APTT values. Unlike samples from healthy subjects, there was no obvious trend of time-related prolongation of the APTT in heparinized plasma. These results led us to believe that within an 8-hour period and with plasma on spun-down cells at room temperature, add-on tests for PT and APTT could be performed with results similar to what would be obtained from testing unstored samples.

Use of Anti-Xa Activity as a Marker for Heparin-Induced Bleeding in Patients with APTT &amp;gt;180 s

Heparin is administered as an anticoagulant in treatment of or prophylaxis against arterial or venous thromboembolism, in treatment of myocardial infarction, and during cardiac surgery (cardiopulmonary bypass) (1), coronary angioplasty, and other procedures (2). Heparin treatment demands laboratory control and is monitored by determining the activated partial thromboplastin time (APTT), which should be adjusted to stay within 1.5–2 times the control value (3). Sometimes during therapy high APTT values (>180 s) are reached (4), and physicians decide to interrupt the treatment for a few hours because of the great risk of hemorrhagic complications, the most important side effect of heparin therapy (5). In these situations, however, the true concentrations of heparin in the patient’s plasma are really unknown. Moreover, in some described cases, the APTT values were prolonged because of underlying disease (severe liver disorders, extensive myocardial infarction, or infection) and postoperative complications after cardiac surgery (6). This prolongation of APTT was not heparin related, although the results of the APTT test falsely suggested a higher heparin concentration (7). Another problem is that sensitivity of the reagents for the APTT test varies greatly, and the physicians who prescribe heparin on the basis of certain APTT ratios may order different doses of heparin and produce different amounts of anticoagulation in their patients (3). In cases with …

Resistance to activated protein C as a basis for venous thrombosis.

In three families with various forms of venous thrombosis, we observed an apparently inherited poor response to the anticoagulant activated protein C (APC). The condition was due to a deficiency in a previously unrecognized anticoagulant factor that functioned as a cofactor to activated protein C. We conducted the present study to determine the prevalence of resistance to APC in patients with venous thrombosis. We compared 104 consecutive patients with venous thrombosis confirmed by objective tests with 130 controls. In addition, 211 members of 34 families of persons with resistance to APC were studied. The anticoagulant response to APC was measured with a modified version of the activated partial-thromboplastin time test; the results were expressed as APC ratios. Forty-five percent of patients had a family history of thrombosis. A significant (P < 0.001) difference in APC ratios was observed between the controls and the patients with thrombosis. For 33 percent of patients, the APC ratio was below the 5th percentile of the control values, although the results of the family studies suggested that the prevalence of APC resistance may be even higher (approximately 40 percent) in the patients with thrombosis. The inherited nature of the defect was confirmed in a majority of cases, and the family studies suggested the mode of inheritance to be autosomal dominant. The thrombosis-free survival of APC-resistant family members was significantly less than that of non-APC-resistant family members. There was a high prevalence of APC resistance among young persons with a history of venous thrombosis, and this resistance appeared to be inherited as an autosomal dominant trait.

Intraoperative measurement of activated partial thromboplastin time and prothrombin time by a portable laser photometer in patients following cardiopulmonary bypass

Intraoperative capabilities to rapidly assess coagulation status following cardiopulmonary bypass (CPB) may be of benefit in providing optimal hemostasis and transfusion management, because CPB causes abnormalities in coagulation that may increase morbidity and mortality. The Ciba Corning 512 coagulation monitor (Ciba Corning, Medfield, MA) is a compact and portable device that rapidly determines the prothrombin time (PT) and activated partial thromboplastin time (APTT) in whole blood samples. One hundred patients requiring CPB had APTT and PT determined in whole blood specimens by the 512 coagulation monitor and in plasma specimens by the hospital laboratory from the same arterial blood sample obtained after protamine administration. Correlation coefficients of 0.95 and 0.77 were obtained for the paired APTT and PT tests, respectively ( P < 0.01). A bias of 12.6 seconds and 0.77 seconds was determined for the APTT and PT, respectively. The 95% confidence intervals of the bias of the APTT and PT were 9.7 seconds to 15.5 seconds and 0.3 seconds to 1.16 seconds, respectively. The 512 coagulation monitor provided APTT and PT results in less than 3 minutes compared to approximately 45 minutes for the hospital laboratory. A reduction in accuracy was associated with the 512 coagulation monitor PT and APTT when different sampling sites were used. The 512 coagulation monitor accuracy was not affected by a variation of hemoglobin concentration or platelet count between 6 and 12 gm/dL and 15 to 300 · 10 9/L, respectively. In conclusion, the 512 coagulation monitor provided a rapid APTT and PT result, but the APTT was less accurate. Speeding access to hospital laboratory results would be even more efficacious and accurate.

Coagulopathy Screening in Children With Heparinized Central Venous Catheters

To develop a method of screening for coagulopathy using blood drawn through heparinized central venous catheters. Prothrombin time (PT) and activated partial thromboplastin time (APTT) were determined in paired blood samples with and without the addition of protamine, using an automated photo-optical method. A concentration of 4 micrograms/mL of citrated whole blood was chosen, based on preliminary experiments. This is sufficient to neutralize the expected heparin contamination in samples drawn through heparinized catheters while causing only a slight prolongation in APTT (due to the anticoagulant effect of protamine). Seventeen paired samples were drawn by venipuncture in patients without known coagulopathy. Twenty-five samples were drawn through heparinized central venous catheters. The first 5 mL of blood drawn from a catheter was discarded to avoid gross heparin contamination. Four samples from patients with coagulopathy were also analyzed with and without the addition of 2.5 micrograms/mL of heparin. Protamine increased PT by 9.0 +/- 0.8% and APTT by 9.0 +/- 3.4% (mean +/- SD) in the samples drawn by venipuncture. For samples drawn through heparinized catheters, 52% had a prolonged APTT, 44% a prolonged PT, and 68% had at least one prolonged test. With the addition of protamine, and after correction for the 9% mean increase in PT and APTT, 4% of samples had a prolonged APTT, 12% had a prolonged PT, and 16% had at least one prolonged test (P = .00006, .014, and .0001). All four samples from patients with coagulopathy were correctly identified as abnormal after the addition of protamine, with or without added heparin. A protamine-supplemented APTT test on blood drawn through a heparinized catheter may be an adequate screening test for coagulopathy. This procedure reduces discomfort in patients with an indwelling catheter by avoiding venipuncture.

The influence of time, temperature and packed cell on activated partial thromboplastin time and prothrombin time

Activated partial thromboplastin time (APTT) and prothrombin time (PT) were performed in four groups of studies in order to evaluate the influences of time, temperature, and different forms of plasma storage to the result. Different designs for storage of the plasmas were studied, including the plasmas stored either with or without packed cells, the plasmas stored in the cuvette with exact volume for performing the test or in the test tube. The temperatures for store of the plasma were at room temperature, at 4°C and at −70°C. The time for store of the plasma was from 1 hour up to 7 hours. The plasmas included normal pooled plasmas and diseased plasmas. From this study, it is found that the PT test was not easily affected by the temperature, storage time and the form of storage in comparison with the APTT test which was much easily affected by the above conditions. APTT should be done within 2 hours after sampling and the plasma should be stored with the packed cells at 4°C in order to obtain a reliable result. PT could be done within 7 hours without influence to the result if the plasma was stored with the packed cells at 4°C. No significant cold-induced shortening of PT could be noted when the plasma was incubated at 4°C up to 7 hours. In either PT or APTT, the most suitable condition for storing the plasma should be with the packed cells at 4°C.

Effect of Sample Volume on Coagulation Tests

This study was undertaken to determine an acceptable range of specimen volumes for routine coagulation tests, that is, the prothrombin time (PT) and activated partial thromboplastin time (APTT) tests. Samples were obtained from healthy volunteers, patients who were receiving warfarin (Coumadin), and patients who were receiving heparin therapy. Specimen volumes, from as little as 3.0 mL to as much as 6.0 mL, were collected from each patient into blue-stoppered evacuated (Vacutainer1) tubes that contained 0.5 mL of 3.8% buffered sodium citrate. Results ofPT and APTT tests from the above specimens were compared with 4.5-mL samples from the same patients that were collected at the same time. Test results in each category of sample volumes, 3.0,3.5,5.5, and 6.0 mL, were compared with the corresponding 4.5-mL sample size. The only statistically and clinically significant difference in test results was in the 3.0-mL sample sizes from healthy volunteers who were tested for APTTs. Although a 4-second difference in the APTT, seen in the 3.5-mL sample size from healthy volunteers, was not statistically significant, this difference may be exaggerated in patients with a higher than normal hematocrit.We can, therefore, recommend that tolerance limits for sample size for commercially available blue-stoppered evacuated tubes that contain 0.5 mL of 3.8% sodium citrate to be at least between 3.5 and 6.0 mL from patients with a normal or lower hematocrit.

Detection of lupus like anticoagulant: current laboratory practice in the United Kingdom. The Lupus Anticoagulant Working Party.

Various tests have been advocated for the detection of lupus like anticoagulants (LA) and related antiphospholipid antibodies, but there is no agreement on the most appropriate laboratory approach. Two hundred and fifty five of 433 hospital centres in the United Kingdom responded to a questionnaire. Many different tests were reported to be in use for screening for LA with considerable variation in plasma preparation, choice of reagent, and methodological details. Three freeze dried plasmas were subsequently assessed for the presence of LA by 183 laboratories. While 92% correctly identified a strong inhibitor and 91% a negative control, only 65% correctly identified a weak inhibitor. Pronounced variations in the suitability of commonly used reagents in the activated partial thromboplastin time test (APTT) were noted and important methodological features were identified in the kaolin clotting time, dilute thromboplastin time, and dilute Russell's viper venom time tests. It is concluded that careful plasma preparation, with avoidance of platelet contamination, use of a suitable test in addition to the APTT, and attention to methodological detail are essential for the reliable identification of LA, a clinically important inhibitor.

Use of the activated partial thromboplastin time for monitoring heparin therapy: problems and possible solutions.

There is considerable variation in available methods for the activated partial thromboplastin time (APTT), giving widely differing results with patients on heparin treatment. The study is primarily concerned with the assessment of five of the widest used APTT reagents. The heparin response of these reagents has been related to their lipid composition and physical properties. Of the various correlations between lipid composition of the reagents and clotting performance only electrophoretic mobility was associated with the APTT response to heparin. There was a highly significant negative correlation between the APTT prolongation with heparin and electrophoretic mobility. When plasma is heparinized in vitro a differing order of ranking for APTT reagents is obtained than when heparinized patients are tested. The APTT response in patients with recent thrombosis must therefore be the best guide to the clinical dose of heparin. The therapeutic range of conventional heparin therapy is generally regarded as 1.5-2.5 times the control. External quality assessment programmes in the UK and USA have shown considerable differences between heparin dosage according to the APTT test systems. The definition of the therapeutic range must be derived from randomized clinical studies. The need for progress in standardization of the APTT monitoring of heparin is demonstrated.