Dilute Thromboplastin Research Articles

Lupus Anticoagulant Testing: Dilute Prothrombin Time (dPT).

Lupus anticoagulants (LA) rarely affect routine prothrombin time assays because the high phospholipid (PL) content in thromboplastin reagents tends to overwhelm the antibodies. Dilution of thromboplastin to create a dilute prothrombin time (dPT) screening test renders the assay sensitive to the presence of LA. Technical and diagnostic performances are enhanced if recombinant thromboplastins are employed in place of tissue-derived reagents. Presence of an LA cannot be deduced from an elevated screening test alone since other coagulation disturbances can prolong clotting times. Confirmatory testing with less dilute or undiluted thromboplastin reveals the PL-dependent nature of LA by reducing the clotting time relative to that of the screening test. Where appropriate, such as a known or suspected coagulation factor deficiency, mixing tests are valuable in correcting factor deficiencies and evidencing inhibitory properties of LA, to increase diagnostic specificity. Although LA testing is commonly restricted to dilute Russell's viper venom time and activated partial thromboplastin time, dPT is sensitive to LA unreactive in those assays, and inclusion in routine testing increases detection rates of clinically significant antibodies.

A single test to assay warfarin, dabigatran, rivaroxaban, apixaban, unfractionated heparin, and enoxaparin in plasma

Essentials Simple and fast assaying of different anticoagulants (ACs) is useful in emergent situations. We used highly diluted prothrombin time (dPT) or highly diluted Fiix-PT (dFiix-PT) to assay ACs. Both tests could quantify target specific anticoagulants and warfarin anticoagulation. Improved results were consistently observed with the dFiix-PT compared with the dPT. Background Assaying anticoagulants is useful in emergency situations or before surgery. Different specific assays are currently needed depending on the anticoagulant. Objectives We hypothesized that levels of warfarin, dabigatran, rivaroxaban, apixaban, and heparins could be measured with use of the diluted prothrombin time (dPT) and diluted Fiix-PT (dFiix-PT), using highly diluted thromboplastin (TP). The latter test is affected only by reduced levels of active factors II and X but corrects test plasma for other deficiencies Methods Increasing TP dilutions were used to identify suitable dilutions to measure dabigatran, rivaroxaban, apixaban, unfractionated heparin (UFH), and enoxaparin. Calibrators containing known amounts of direct oral anticoagulants (DOACs) were used to make standard curves. Citrated plasma samples were obtained from patients taking warfarin or DOACs with known drug concentrations as determined by specific assays. Results The dFiix-PT at a TP dilution of 1:1156 could be used to measure all of the drugs tested at therapeutic concentrations except for fondaparinux. The dPT achieved the same but required two TP dilutions (1:750 and 1:300). The warfarin effect could be assessed by using dFiix-PT at 1:1156 with a PT ratio identical to the international normalized ratio. Six different TPs yielded similar results, but two were less sensitive. Dabigatran, rivaroxaban, and apixaban could be accurately measured in patient samples using both dilute PT assays, but a better correlation was consistently observed between the dFiix-PT and specific assays than with the dPT. Conclusion The dFiix-PT using a single dilution of TP may be suitable to assess the anticoagulant effects of warfarin, dabigatran, rivaroxaban, apixaban, heparin, and enoxaparin.

Coagulation Induced by Dilute Tissue Factor Depends More Critically on Factor II and X Concentration Than on FVII or FIX

Prothrombin time based tests used to monitor coumarin anticoagulation measure the initiation phase of fibrin formation (clotting time, CT) in platelet poor plasma. Additional information can be obtained using computerized rotational thromboelastometry (ROTEM) which also measures the consequent propagation phase (measured as maximum velocity, Vmax), and the stabilization phase (maximum clot firmness, MCF).We used ROTEM to study the effect of individual vitamin K dependent (VK) coagulation factor (F) concentration on clotting induced by dilute thromboplastin in platelet poor and platelet rich plasma (PPP and PRP).As expected, FII, FVII and FX in PPP equally affected the prothrombin time whereas FIX did not. In PPP the ROTEM CT, however, was affected more by the concentration of FII and FX than by FVII (data not shown). To imitate physiological clotting better, factor deficient platelet poor plasma was repleted by adding frozen platelets in an optimal concentration corresponding to 100 × 109/L.. In the PRP the ROTEM CT was more dependent on the concentration of FII than of FVII, more dependent on FX than on FII and not dependent on FIX at all (left figure). The Vmax (reflecting the propagation phase) was also more dependent on FII and factor X than on the concentration of FVII or FIX which both may demonstrate a threshold effect (right figure). The stabilization phase or maximum clot firmness (MCF, not shown) was influenced similarly by FII and FX but was not influenced by FVII or FIX. [Display omitted] Conclusion: During deficiency of vitamin K dependent coagulation factors the concentration of FII and FX may be more critical for hemostasis than FVII or FIX concentration. This may have practical implications for the appropriate choice of monitoring assays during coumarin administration.

Effect of substrate and fibrin polymerization inhibitor on determination of plasma thrombin generation in vitro

Background Thrombin generation potential, a critical haemostatic measure, can be determined by continuous detection of total thrombin or direct subsampling. However, differences between methods exist in area under the curve or peak thrombin calculated. Also, impact of anticoagulants on thrombin generation may vary depending on mode of analysis. Objective We studied the effect of components on thrombin generation in the presence or absence of anticoagulants. Methods The continuous method was conducted with plasma ± fibrin(ogen) ± fibrin polymerization inhibitor. Plasma contained slow-reacting TG5134 substrate at 37 °C and reaction was started with dilute thromboplastin in CaCl 2/Tris buffer. Absorbance (405 nm) was recorded over time and free thrombin calculated from total thrombin activity. For the subsampling method, similar plasma mixtures ± TG5134 were reacted and free thrombin measured directly as the difference in activity against S2238 substrate of timed subsamples taken into EDTA or EDTA + antithrombin + heparin. Results Slow-reacting substrate in the continuous method acted as a competitor for thrombin, giving delayed but greater free thrombin than direct subsampling. These differences persisted to varying extents with all anticoagulants tested. In either method, presence of polymerization inhibitor increased the amount of free thrombin. Continuous method detection of α 2macroglobulin complexes was hampered by sensitivity limits leading to inordinate free thrombin calculations. Especially with hirudin, although free thrombin remained at the end of the subsampling method, continuous method calculations assumed no residual free thrombin. Conclusion In vitro plasma thrombin generation is delayed and increased by slow-acting substrate and fibrin polymerization inhibitor.

Towards a standardization of thrombin generation assessment: The influence of tissue factor, platelets and phospholipids concentration on the normal values of Thrombogram-Thrombinoscope assay

BackgroundThrombin generation assay was developed several years ago to mimic physiological coagulation mechanisms but it had important limitations. Thrombogram-Thrombinoscope assay using a fluorogenic substrate, allows obtaining thrombin generation curves in non-defibrinated platelet rich plasma (PRP) in a fully automated manner.MethodsWe standardised the methodology of Thrombogram-Thrombinoscope and we evaluated the precision of thrombin generation parameters (lag-time, maximum concentration of thrombin [Cmax], time required to reach Cmax [Tmax] and endogenous thrombin potential ETP) using different concentrations of recombinant human tissue factor, platelets or phospholipids. Normal values of thrombin generation assay were established in optimal experimental conditions.ResultsIn the presence of low TF concentrations (final dilution of thromboplastin in plasma: 1/1000–1/2000) the Thrombogram assay showed intra-assay and inter-assay coefficients of variation lower than 9%. Thrombin generation parameters showed an important inter-individual variability and the coefficients of variation ranged from 18% to 50%. In PRP the lag-time, Cmax and Tmax but not the ETP, were influenced by TF concentration. Thrombin generation parameters were not influenced by variations of platelet concentration from 50 × 109/l to 400 × 109/l. The addition of synthetic procoagulant phospholipids in PPP strongly influenced all the parameters of thrombogram. For all the parameters of thrombogram a threshold effect was observed in the presence of phspholipid concentrations equal or higher to 4 μM. In frozen-thawed PRP the lag-time and the Tmax were significantly reduced and the Cmax was increased compared to the fresh PRP, but the ETP, the intra assay and the inter-assay coefficients of variation were similar in both test-systems.ConclusionThrombogram-Thrombinoscope assay performed in fresh or in frozen-thawed PRP has an acceptable precision, with low inter-assay and intra-assay coefficient of variations. The concentration of TF is determinant for the normal values of the studied parameters of thrombin generation. When the assay is performed in PPP, thrombin generation parameters are influenced by the concentration of procoagulant synthetic phospholipids. The optimal experimental conditions were obtained in the presence of 1/1000 final dilution of thromboplastin, a platelet count higher than 50 × 109/l and a synthetic phospholipid concentration higher than 4 μM.

A Case of IgM- λ Waldenström's Macroglobulinemia with Activity Against Phospholipids, Masquerading as Factor V Inhibitor.

Background: The Lupus anticoagulant is known to prolong coagulation tests, however the source of antibody causing this prolongation is not clear in the majority of patients. We are reporting a patient with prolongation of prothrombin time (PT) and activated partial thromboplastin time (aPTT) secondary to a lupus anticoagulant like activity of an IgM paraprotein.Case report: An 82 years old male patient was referred in January 1996 to our clinic for abnormal PT and aPTT. He was asymptomatic. There was no lymphadenopathy or organomegaly. The hemoglobin was 10.4 (g/dl) with normal white cell and platelet count. Renal and liver function tests were normal. Coagulation studies revealed aPTT 145.4 seconds, the PT 38.8 seconds, thrombin time 24.9 seconds, fibrinogen level of 336 mg/dl and D Dimer <500. In-vitro mixing studies with normal plasma failed to correct the prolongation of the clotting tests without and with incubation for 1 hour. This suggested the presence of an inhibitor. Factor inhibitor assays were done that suggested the presence of a factor V inhibitor (14.8 Bethesda units). The apparent lower level inhibitory activity against other factors II, VII and X was presumed to be due to inhibition of prothrombinase complex by factor V inhibitor. Agarose affinity column chromatography with factor V bound to the agarose did not remove the PT inhibitory activity. A lupus anticoagulant was suspected when the PT and aPTT of normal pooled plasma was prolonged by the addition of patient's plasma. The patient's plasma with pooled normal plasma gave a positive dilute thromboplastin inhibition test, 1:50 dilution >3.1 and 1:500 dilution >2.9 (normal <1.3) as well as a positive PNP (platelet neutralization procedure) as evidenced by a shortening of aPTT from >106 seconds to 48 seconds upon the addition of platelet phospholipids (a difference of >5 sec is taken as positive for LA). Expanded antiphospholipid antibodies test were done. Anti-cardiolipin IgM (>100MPL), anti-phosphotidyl serine IgM (7.3SD) were detected. A serum protein electrophoresis revealed monoclonal gamma spike of approximately > 4gm/dl and quantitative immunoglobulin by radial immuno-diffusion (RID) showed IgG- 1691 mg/dl, IgA - 185 mg/dl, IgM >192 mg/dl. The IgM >192 mg/dl is limited by the linearity of the test. IFE (Immunoelectrophoresis) demonstrated IgM-λ spike. Serum viscosity was 3.4. We suspected that the IgM paraprotein might be the inhibitor. IgM was purified by Euglobulin flocculation test. The PT and aPTT of normal pooled plasma was prolonged on its addition. The conclusion was that antiphospholipid activity was in IgM. Bone marrow biopsy in January 1996 showed <10% of plasmacytoid lymphocytes. Repeat bone marrow biopsy in December 1997 showed increased plasmacytoid cells to 60%. In view of increased serum viscosity to 4.3 and bone marrow biopsy findings as above, a diagnosis of progressive Waldenström's Macroglobulinemia was established. In addition to intermittent plasmapheresis, an oral chlorambucil (0.25mg/kg) q21 day was given for 14 months from December 1997, with a decrease in paraproteins, serum viscosity and PT, aPTT. Patient remained asymptomatic till March 2002 when he developed clinically progressive disease as evidenced by hepatosplenomegaly. He refused all investigations and interventions at this time and was lost to follow up. During the entire follow up period lasting 6 years he did not demonstrate any bleeding or thrombotic tendency.

Roles of factor XI, platelets and tissue factor-initiated blood coagulation

Roles of factor XI, platelets and tissue factor-initiated blood coagulation

The Role of Factor XI in a Dilute Thromboplastin Assay of Extrinsic Coagulation Pathway

Blood coagulation has been thought to be composed of both intrinsic and extrinsic pathways. Recent evidence strongly supports the critical role of the extrinsic pathway in the initiation of blood coagulation. This investigation established an assay that examines the role of FXI in the thromboplastin-initiated (extrinsic) coagulation based on this new concept. Plasma clotting times were measured at different concentrations of thromboplastin with activated FXII inhibited (FXIIa-inhibited Diluted Thromboplastin Time, FXIIaiDTT). Only at low concentrations of thromboplastin was FXIIaiDTT of FXI-deficient plasma significantly prolonged than that of normal plasma. Depletion of FXI from normal plasma prolonged its FXIIaiDTT and replenishment of FXI shortened it. FXIIaiDTTs of both FVIII-deficient and FIX-deficient plasma were remarkably prolonged, and addition of normal plasma dose-dependently shortened it. Furthermore, earlier alpha-thrombin inhibition was directly correlated with decreasing FXa generation. The amount of FXa production was: platelet-rich plasma > platelet-poor plasma > FXI-deficient plasma. Therefore, our findings from the FXIIaiDTT assays not only support the critical role of extrinsic pathway in blood coagulation initiation, but also demonstrate the importance of FXI as an amplifier of thrombin generation in thromboplastin-initiated coagulation.

Influence of exogenous factor VIIa on thrombin generation in cord plasma of full-term and pre-term newborns.

Factor (F) VIIa has been used to treat adults and children with a variety of bleeding disorders. The results from these studies cannot be extrapolated to newborns because their hemostatic system differs significantly from adults, which may influence the effects of FVIIa on thrombin (IIa) generation. We compared the effects of FVIIa concentrates on IIa generation in plasmas from adults, full-term newborns and pre-term newborns. Defibrinated plasma (using arvin) from adults, or umbilical cords from full-term or pre-term deliveries was supplemented with FVIIa (Novo Nordisk, Bagsvaerd, Denmark), mixed with dilute thromboplastin reagent, and the resultant reaction mixture subsampled periodically into ethylenediamine tetraacetic acid, followed by measurement of total IIa activity (S-2238). Thrombin-alpha2 macroglobulin complexes, determined as residual activity after neutralization with heparin and antithrombin, were subtracted from total IIa to give free IIa. Prothrombin (FII) and inhibitor complexes were measured by enzyme-linked immunosorbent assays. Addition of FVIIa caused a reduction in the lag phase for the appearance of free IIa and consumption of FII, which was more pronounced in newborn plasma. There was no increase in peak IIa levels regardless of the amount of FVIIa added. Final inhibitor complex concentrations were increased in plasmas from adults compared with newborns, likely reflecting higher plasma concentrations of FII in adults. Generation of IIa was more rapid in pre-term plasma compared with that in adult and full-term cord plasmas due to increased endogenous tissue factor (TF). In summary, FVIIa enhanced IIa generation in plasma from different age groups, with the effect being more pronounced in plasma from pre-term newborns, possibly due to increased levels of plasma TF.

A review of 100 consecutive patients with spontaneous or recurrent thrombosis

One hundred consecutive patients referred to the Royal Melbourne Hospital, Diagnostic Haematology Department for investigation of a possible hypercoagulable state were analysed 1) to determine the prevalence of congenital deficiencies of the naturally occurring anticoagulant protein C, protein S, antithrombin III and plasminogen, 2) the prevalence of acquired disorders, eg: antiphospholipid syndrome and abnormal fibrinolytic activity, and 3) whether there were clinical features associated with the inherited disorders that would identify high risk patients to allow more effective application of these tests. All patients referred were screened by the following tests: FBE, PT, APTT, thrombin time, fibrinogen, D-dimer, filtered APTT, lupus anticoagulant screening by dilute thromboplastin time and dilute Russell Viper venom time, protein C functional assay, protein S free and bound, anthithrombin III functional assay and plasminogen. Anticardiolipin assays were also performed. The age range of patients was 12-93 years, median 44 years. Both venous and arterial thrombi were studied, ratio 6:1. Abnormalities of the fibrinolytic system occurred in 35%, lupus anticoagulants in 13%, deficiencies of antithrombin III in 2%, protein C in 2% and plasminogen 2%. Neither age, documented family history, nor gender were useful in identifying patients with a detectable abnormality. The incidence of deficiencies of naturally occurring anticoagulants were similar to those previously reported. Protein S deficiency was not detected. The antiphospholipid syndrome and reduction in post stress fibrinolysis were the most frequently detected abnormalities. This suggests the need for greater understanding of the role of the fibrinolytic system in recurrent thrombosis.

Effect of lipoprotein-associated coagulation inhibitor (LACI) on thromboplastin-induced coagulation of normal and hemophiliac plasmas

Lipoprotein-associated coagulation inhibitor (LACI) is a plasma-derived protein that inhibits the tissue factor/factor VIIa/calcium/phospholipid complex in a factor Xa-dependent manner. Recombinant LACI (rLACI) added exogenously to plasma prolonged the activated partial thromboplastin time (APTT) and prothrombin time (PT) as a function of rLACI concentration in linear and curvilinear manners, respectively. Under these standard assay conditions, the amounts of rLACI required to double the APTT and PT were approximately 350-and 90-fold the plasma concentration of LACI, respectively. Likewise, addition of antibodies against LACI to pooled normal, factor VIII-deficient, or factor IX-deficient plasma had no effect on their respective APTTs and PTs, demonstrating the insensitivity of these assays to endogenous LACI. The prothrombin time assay was modified by using dilute thromboplastin. Unlike the standard prothrombin time assay, the clotting times were prolonged for factors VIII-or IX-deficient plasma relative to pooled normal plasma in this modified PT assay. Additionally, the degree of factor deficiency, as determined by the APTT assay, was correlated with that determined by the modified PT assay using dilute thromboplastin. When antibodies against LACI were added to pooled normal, factor VIII-deficient, or factor IX-deficient plasma and the prothrombin time assay initiated using dilute thromboplastin, the clotting times for antibody-treated plasma were shorter than for the corresponding plasma in the absence of antibodies. Moreover, the clotting times for factors VIII-and IX-deficient plasmas treated with antibodies raised against LACI were at least as fast as pooled normal plasma in the absence of LACI antibodies when dilute thromboplastin was used to initiate clotting. These results suggest that the prothrombin time assay using dilute thromboplastin may more accurately reflect what occurs in vivo and that LACI may play an important role in the prolonged bleeding of those with hemophilia A or B.

Inhibition of Extrinsic Pathway Inhibitor Shortens the Coagulation Time of Normal Plasma and of Hemophilia Plasma

An increasing amount of evidence suggests that coagulation factors VIII and IX play a role not only in the intrinsic but also in the extrinsic pathway of coagulation. In this context the influence of the Extrinsic Pathway Inhibitor (EPI) on the coagulation time of hemophilia plasma lacking FVIII or FIX has been investigated. The coagulation time was measured in a dilute thromboplastin assay. Addition of recombinant EPI (rEPI) prolonged the coagulation time of normal plasma while the addition of an inhibitory antibody against EPI shortened the coagulation time. At low concentrations of thromboplastin the coagulation time of hemophilia plasma was prolonged and at all dilutions of thromboplastin, addition of anti-EPI IgG normalized the coagulation time of a hemophilia plasma. Analysis of 10 individual donor plasma samples and 8 individual hemophilia samples showed that addition of anti-EPI IgG shortened the coagulation time more in hemophilia plasma than in normal plasma. This illustrates the importance of a powerful extrinsic FVII dependent pathway to achieve hemostasis in the case of FVIII or FIX deficiency (hemophilia A and B).

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.

Decreased fibrinolytic capacity and increased von Willebrand factor levels as indicators of endothelial cell dysfunction in patients with lupus anticoagulant

Over a 6-year period, 10 patients with lupus anticoagulant activity were seen. A history of thrombotic disease was found in 6 patients, but only 3 had systemic autoimmune disease. Reduced fibrinolytic activity after venous occlusion was found in 9 subjects, but only 4 had high von Willebrand factor levels. These changes were unrelated to inflammatory activity, which was ruled out by normal serum protein electrophoresis in all but one case. Human brain thromboplastin dilution test was pathological in all subjects with depressed fibrinolytic activity. These two tests may prove to be of value to single out those LA patients with highest risk for development of thromboembolic disease.

Familial lupus anticoagulants.

Three families having more than one affected member with SLE or lupus-like disease were investigated by global coagulation tests as well as methods based on dilute thromboplastin, Russell's viper venom and thermal stability/absorption, and by RIA for anticardiolipin (CL) antibodies. Of the 19 persons, 11 had SLE or lupus-like disease. Eight of these 11 had a prolonged KPTT and other evidence of LA, while only 5/11 had high anticardiolipin titres. Four healthy spouses of affected females, and three asymptomatic siblings also had prolonged non-correctable KPTTs. These persons had no bleeding or thrombotic history and normal clotting factor levels. Further clotting tests were negative, although one had raised anti-CL antibody. Such cases may account for some of the patients one finds during routine haemostatic screening with unexplained prolonged KPTT. Although anticardiolipin levels are raised in subjects with LA, there was no close correlation between length of KPTT and anticardiolipin titre. These findings would support a hypothesis of transmissible agents or other environmental factors being involved in lupus-like disorders.

Lupus anticoagulants: improved diagnosis with a kaolin clotting time using rabbit brain phospholipid in standard and high concentrations

We utilized a kaolin-activated partial thromboplastin time (APTT) using rabbit brain phospholipid, in which the capacity of a fourfold increased “high” phospholipid concentration (PC) to normalize the abnormal “standard” PC-APTT in patients with lupus anticoagulants is assessed. This system was also used to measure factors VIIIC, IX, and XI. The tissue thromboplastin inhibition test (TTI), a prothrombin time system in which the activity of a lupus anticoagulant is unmasked by the use of dilute thromboplastin, was simultaneously evaluated. Test sensitivity was defined by results on 31 consecutive patients with standard PC-APTT inhibitors and no bleeding tendency. Specificity was based on 94 patients with various other coagulopathies, including coagulation factor inhibitors, severe congenital factor deficiencies, hepatic insufficiency, and warfarin and heparin treatment. Twenty-one patients with lupus erythematosus and standard PC-APTT results within normal limits were also tested. Sensitivity of the APTT system was superior to that of the TTI (97% v 58%); high PC normalized clotting time ratios and factor levels. Positive results were common with both assays in the group of 20 heparinized patients. The APTT system had superior specificity in remaining cases; there were no positive tests among 74 patients. The lupus erythematosus group had a significant decrease in the clotting time ratio with high PC, indicating that low- level lupus anticoagulants are quite prevalent in this group. The kaolin clotting time using rabbit brain phospholipid in standard and high concentrations is a simple, sensitive, and specific technique for diagnosis of lupus anticoagulants.

Lupus Anticoagulants: Improved Diagnosis With a Kaolin Clotting Time Using Rabbit Brain Phospholipid in Standard and High Concentrations

We utilized a kaolin-activated partial thromboplastin time (APTT) using rabbit brain phospholipid, in which the capacity of a fourfold increased "high" phospholipid concentration (PC) to normalize the abnormal "standard" PC-APTT in patients with lupus anticoagulants is assessed. This system was also used to measure factors VIIIC, IX, and XI. The tissue thromboplastin inhibition test (TTI), a prothrombin time system in which the activity of a lupus anticoagulant is unmasked by the use of dilute thromboplastin, was simultaneously evaluated. Test sensitivity was defined by results on 31 consecutive patients with standard PC-APTT inhibitors and no bleeding tendency. Specificity was based on 94 patients with various other coagulopathies, including coagulation factor inhibitors, severe congenital factor deficiencies, hepatic insufficiency, and warfarin and heparin treatment. Twenty-one patients with lupus erythematosus and standard PC-APTT results within normal limits were also tested. Sensitivity of the APTT system was superior to that of the TTI (97% v 58%); high PC normalized clotting time ratios and factor levels. Positive results were common with both assays in the group of 20 heparinized patients. The APTT system had superior specificity in remaining cases; there were no positive tests among 74 patients. The lupus erythematosus group had a significant decrease in the clotting time ratio with high PC, indicating that low-level lupus anticoagulants are quite prevalent in this group. The kaolin clotting time using rabbit brain phospholipid in standard and high concentrations is a simple, sensitive, and specific technique for diagnosis of lupus anticoagulants.

Circulating coagulation inhibitors in the acquired immunodeficiency syndrome.

Abnormal coagulation profiles were identified in ten patients with the acquired immunodeficiency syndrome (AIDS) associated with opportunistic infections and malignancies. Activated partial thromboplastin times were elevated in all patients; three of seven had elevated prothrombin times. All patients had lupus-type anticoagulants characterized by rapid prolongations of the partial thromboplastin time in mixing studies, prolonged dilute thromboplastin inhibition assays, and increased Russell viper venom clotting times. Ivy bleeding times were prolonged in three patients with defective platelet aggregation. The lupus anticoagulant was isolated from the sera of healthy heterosexual men and from patients with AIDS with and without the lupus anticoagulant, and in the presence and absence of opportunistic infections. Both polyclonal IgM and IgG lambda from plasma with lupus anticoagulant interfered with clotting studies and platelet aggregation. The inhibitors usually accompanied active opportunistic infections and tended to disappear with successful resolution of infection.

An alternative extrinsic pathway of human blood coagulation

To study the interrelationships of the major human coagulation pathways, factor X activation in normal and various deficient human plasmas was evaluated when clotting was triggered by dilute rabbit or human thromboplastin. Various dilutions of thromboplastin were added to plasma samples containing 3H-labeled factor X, and the time course of factor X activation was determined. At a 1/250 dilution of rabbit brain thromboplastin the rate of factor X activation in factor VIII or factor IX deficient plasma was only 10% of the activation rate seen for normal or factor XI deficient plasma. Reconstitution of the deficient plasmas with factors VIII or IX, respectively, restored normal factor X activation. Similar results were obtained when various dilutions of human thromboplastin replaced the rabbit thromboplastin. From these experiments, it is inferred that normal activation of factor X in plasma due to dilute thromboplastin requires factors VII, IX and VIII. An alternative extrinsic pathway that involves factors VII, IX, and VIII may be a major physiologic extrinsic pathway, and this pathway may help to explain the clinical observations of bleeding diatheses in patients deficient in factors IX or VIII.

An alternative extrinsic pathway of human blood coagulation

AbstractTo study the interrelationships of the major human coagulation pathways, factor X activation in normal and various deficient human plasmas was evaluated when clotting was triggered by dilute rabbit or human thromboplastin. Various dilutions of thromboplastin were added to plasma samples containing 3H-labeled factor X, and the time course of factor X activation was determined. At a 1/250 dilution of rabbit brain thromboplastin the rate of factor X activation in factor VIII or factor IX deficient plasma was only 10% of the activation rate seen for normal or factor XI deficient plasma. Reconstitution of the deficient plasmas with factors VIII or IX, respectively, restored normal factor X activation. Similar results were obtained when various dilutions of human thromboplastin replaced the rabbit thromboplastin. From these experiments, it is inferred that normal activation of factor X in plasma due to dilute thromboplastin requires factors VII, IX and VIII. An alternative extrinsic pathway that involves factors VII, IX, and VIII may be a major physiologic extrinsic pathway, and this pathway may help to explain the clinical observations of bleeding diatheses in patients deficient in factors IX or VIII.