Gerinnungsbestimmungen am Zentrifugalanalysator - Messungen mit chromogenen Substraten und mit der Fibringerinnung

Ziel aller traditionellen Gerinnungstests ist die Fibrinogenumwandlung in Fibrin durch Thrombin. Die Gerinnselbildung wird entweder mechanisch oder photooptisch gemessen. Die Entwicklung chromogener Substrate zur Bestimmung von Gerinnungsenzymen hat eine spektrophotometrische Erfassung der Enzymreaktionen ermöglicht, die zur Automatisierung der Analysen mittels Zentrifugalanalysatoren im klinisch chemischen Laboratorium geführt hat.

Das von Instrumentation Laboratory (IL) entwickelte Automated Coagulation Laboratory (ACL)-System bietet Zentrifugalanalysatoren, die nicht nur Fibringerinnungstests, sondern auch chromogene Substrattests weitgehend automatisch durchführen (ACL 200, und 300 und 300 Research). Die Tests sind bei den 200und 300-Geräten vorprogrammiert, mit dem 300-Research-Gerät ist dagegen diese Vorprogrammierung zu umgehen. Somit können mit dem Gerät fast unbegrenzt neue Einphasenoder Zweiphasentests unter Verwendung von Gerinnungsverfahren oder chromogenen Substraten entwickelt werden. Das ACL-System ist einfach zu bedienen, hat eine ausgezeichnete Präzision und Reproduzierbarkeit und wirkt durch Automatisierung und niedrige Testvolumina kostendämpfend.

Protein C und S

Protein C oder Autoprothrombin II-A ist ein Vitamin-K-abhängiges Glykoprotein mit einem Molekulargewicht von etwa 62000 Dalton. Seine Aminosäurensequenz und andere physikalisch-chemische Eigenschaften haben eine gewisse Ähnlichkeit mit Faktor X. Es kann in vitro durch Thrombin, Trypsin und das Gift der Russell-Viper in seine enzymatische Form, Protein Ca, umgewandelt werden. In seiner aktiven Form ist Protein C ein doppelkettiges Protein, das das aktive enzymatische Zentrum mit Serin in der schweren Kette hat und eine Anzahl γ-Karboxyglutaminsäure-residuen an der leichten Kette.

Die In-vivo-Aktivierung des Protein C durch Thrombin bedarf der Anwesenheit eines gefäßwandständigen Proteins, Thrombomodulin. Das an Thrombomodulin gebundene Thrombin (äquimolare Komplexe) verliert seine Gerinnungsaktivität und seine Plättchenwirkung, nimmt jedoch eine neue Aktivität an, nämlich Protein C in Ca umzuwandeln. Diese Aktivierung erfolgt in Gegenwart von Kalziumionen an Oberflächen. Antithrombin III kann auch das an Thrombomodulin gebundene Thrombin inaktivieren. Eine alternative, jedoch langsamere Protein-C-Aktivie-rung scheint durch Thrombin und Faktor Va möglich zu sein.

Protein Ca hemmt die Gerinnung, indem es proteolytisch die Faktoren Va und Villa zerstört. In dieser Reaktion übernimmt ein weiteres Vitamin-K-abhängiges Protein, Protein S, eine Kofaktorfunktion. Protein Ca aktiviert auch das fibrinolytische System, indem es den Plasminogengewebsakti-vator von der Gefäßwand freisetzt.

Protein Ca wird durch einen spezifischen Protein-Ca-Inhibitor im Plasma inaktiviert, wobei eine ähnliche Komplexbildung zustande kommt, wie sie für Antithrombin und seine zu inaktivierenden Enzyme bekannt ist.

Protein C kann immunologisch (Laureil und ELISA-Technik) und funktionell (synthetische Substrate) bestimmt werden, wobei das Fehlen von Thrombomodulin die funktionellen Methoden unsicher macht.

Protein S, das als Kofaktor für Protein Ca dient, ist auch ein Vitamin-K-abhängiges Glykoprotein mit einem Molekulargewicht von etwa 69000 Dalton. Neben seiner Kofak-toraktivität für Protein Ca kann es offenbar das hochmolekulare C4b-Bindeprotein an Oberflächen binden und somit die Aktivierung des Komplementsystems an Zelloberflächen steuern.

Angeborene und erworbene Pro-tein-C-Mangelzustände führen zu schweren rezidivierenden venösen Thromboembolien, die klinisch dem Antithrombinmangel ähneln. Der angeborene Protein-C-Mangel hat einen autosomal dominanten Erbgang, und die meisten beschriebenen Fälle waren heterozygot. Homozygote Pro-tein-C-Mangelzustände führen zu massiven, tödlichen Thrombosen. Heterozygote Patienten können mit oralen Antikoagulantien und mit Heparin behandelt werden. Einige Patienten erlitten Haut- und Fettnekrosen während der Einleitung der Therapie mit oralen Antikoagulantien. Diese beruhen möglicherweise auf dem schnellen Aktivitätsabfall von Protein C im Plasma.

Der erste Fall von angeborenem Protein-S-Mangel ist ebenfalls durch rezidivierende venöse Thromboembolien gekennzeichnet.

Die Hypothese, daß die autosomal dominanten Faktor-V/VIII-Kombina-tionsdefekte auf einem Mangel von Protein-C-Inhibitor beruhen, hat sich als nicht richtig erwiesen.

Disseminated intravascular coagulation (DIC)

DIC is a life-threatening complication of several disease states. It is characterized by systemic activation of the hemostasis system. In many instances the release of tissue factor (TF) from endothelial cells or other circulating cells triggers the system. Initially, the increased activation can be compensated for by the natural inhibitor systems, a state referred to as compensated DIC. As the trigger persists, inhibitors will be consumed leading to more coagulation. In this process many clotting factors, most notably fibrinogen and platelets are consumed, resulting eventually in a complete breakdown of the hemostasis system. This results in a profuse and diffuse bleeding tendency or decompensated DIC. The term consumptive coagulopathy denotes this process. Of crucial importance is the fate of fibrin that is formed from fibrinogen by thrombin. If the fibrinolytic system is insufficiently activated, fibrin will be deposited in the microcirculation leading to MODS. This will not occur if the fibrinolytic system is fully activated. The clinical suspicion of DIC must be confirmed by laboratory tests and decreasing fibrinogen levels and platelet counts support the diagnosis. The determination of D-dimer, fibrin(ogen) split products (FSP) and soluble fibrin monomer (FM) further support the diagnosis. FM suggest the presence of thrombin, FSP the generation of plasmin, and D-dimer, both thrombin and plasmin. While the tests are not specific for DIC, they can be helpful, in the proper clinical setting, to diagnose decompensated or acute DIC. The tests are not useful for the diagnosis of compensated DIC, except for D-dimer, FSP, and FM if elevated. Compensated DIC can be diagnosed by molecular markers of in vivo hemostasis activation, such as thrombin-antithrombin (TAT) complexes, prothrombin fragment 1 + 2 (F 1 + 2), or plasmin-antiplasmin (PAP) complexes. For the treatment of DIC it is imperative to remove the triggering underlying disease. The consumption of coagulation constituents can be corrected by cryoprecipitate, platelet concentrates, and fresh frozen plasma, if needed. This may reduce the bleeding tendency. Arrest of the activated hemostasis system by heparins, either subcutaneous in low doses or intravenous in therapeutic doses, is only recommended in patients with compensated DIC. If the patient bleeds, heparins should not be given. The administration of concentrates of natural anticoagulants, i.e., antithrombin, protein C, or tissue factor pathway inhibitor are safer than heparins since they do not exacerbate the bleeding tendency. These concentrates were found to be very effective in animal models of DIC; human experience is still limited. Generally, the earlier treatment is initiated, the better the patient's prognosis.

Oral contraceptive pills and hormonal replacement therapy and thromboembolic disease

The risk of thromboembolic complications with the use of second and third generation oral contraceptives is minimal and probably related to underlying congenital or acquired thrombophilic states. Estrogen dose-dependency leads to increased thrombin generation and increased plasmin generation. There is no convincing evidence that the balance between clotting and fibrinolysis is disturbed. The risk of venous thromboembolism with pregnancy is greater than with oral contraceptives. Hormone replacement therapy is safe for healthy women, and the benefits far outweigh the potential risks.

Sticky platelet syndrome

The sticky platelet syndrome (SPS) is an autosomal dominant platelet disorder associated with arterial and venous thromboembolic events. It is characterized by hyperaggregability of platelets in platelet-rich plasma with adenosine diphosphate (ADP) and epinephrine (type I), epinephrine alone (type II), or ADP alone (type III). Clinically, patients may present with angina pectoris, acute myocardial infarction (MI), transient cerebral ischemic attacks, stroke, retinal thrombosis, peripheral arterial thrombosis, and venous thrombosis, frequently recurrent under oral anticoagulant therapy. Clinical symptoms, especially arterial, often present following emotional stress. Combinations of SPS with other congenital thrombophilic defects have been described. Low-dose aspirin treatment (80 to 100 mg) ameliorates the clinical symptoms and normalizes hyperaggregability. The precise etiology of this defect is at present not known, but receptors on the platelet surface may be involved. Normal levels of platelet factor 4 (PF4) and beta-thromboglobulin in plasma suggest that the platelets are not activated at all times; they appear to become hyperactive upon ADP or adrenaline release. In vivo clumping could temporarily or permanently occlude a vessel, leading to the described clinical manifestations. The syndrome appears to be prominent especially in patients with unexplained arterial vascular occlusions.

The effects of a low-dose monophasic preparation of levonorgestrel and ethinyl estradiol on coagulation and other hemostatic factors

OBJECTIVE

This study was undertaken to evaluate the effects on hemostatic factors of a low-dose preparation of levonorgestrel and ethinyl estradiol in a 12-cycle study.

STUDY DESIGN

Thirty healthy women began taking 100 microg levonorgestrel and 20 microg ethinyl estradiol on the first day of the menstrual cycle, continued to take the preparation for the next 21 days, and then took placebo for 7 days. Mean changes in prothrombin time, partial thromboplastin time, and levels of factors VII and X, antithrombin, plasminogen, fibrinogen, protein S, thrombin-antithrombin complexes, and D-dimer were analyzed at baseline and at cycles 3, 6, and 12 with paired Student t tests.

RESULTS

Factor X, plasminogen antigen and activity, and D-dimer levels were significantly increased (P </=.01) during all 3 cycle periods. Antithrombin antigen and protein S total antigen levels were significantly (P </=.001 ) decreased at cycles 3, 6, and 12, whereas factor VII and protein S activity levels were significantly (P </=.05) decreased at cycle 3 and at cycles 3 and 6, respectively.

CONCLUSION

The effects on hemostatic factors in healthy women of a monophasic preparation of 100 microg levonorgestrel and 20 microg ethinyl estradiol were similar to those of other low-dose oral contraceptives.

Low molecular weight heparins and heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) and HIT thrombosis syndrome (HITTS) are immune-mediated complications of clinical use of unfractionated heparin (UFH). The antibody/antigen complex is composed of heparin and platelet factor 4. This complex not only activates platelets but also the clotting system leading to thrombin generation. This explains the thrombosing tendency of these patients, and venous and arterial thromboembolisms are encountered with a morbidity and mortality of about 25-37%. The incidence of HIT is about 3% when UFH is administered therapeutically. The diagnosis is at this time based on clinical observations, especially a sudden, unexplained drop in platelet counts without other reasons. Laboratory tests can be used to confirm the clinical diagnosis, but none of the available tests is 100% reliable. There is no test that will predict HIT and no test that will signal the development of HITTS. Treatment consists of discontinuation of UFH in any form and anticoagulation with danaparoid or r-hirudin, if needed. The use of low molecular weight heparins instead of UFH could largely (not totally) alleviate the problem.

PFA-100 system: a new method for assessment of platelet dysfunction

The PFA-100 system is a platelet function analyzer designed to measure platelet-related primary hemostasis. The instrument uses two disposable cartridges: a collagen/epinephrine (CEPI) and a collagen/ADP (CADP) cartridge. Previous experience has shown that CEPI cartridges detect qualitative platelet defects, including acetylsalicylic acid (ASA)-induced abnormalities, while CADP cartridges detect only thrombocytopathies and not ASA use. In this seven-center trial, 206 healthy subjects and 176 persons with various platelet-related defects, including 127 ASA users, were studied. The platelet function status was determined by a platelet function test panel. Comparisons were made as to how well the defects were identified by the PFA-100 system and by platelet aggregometry. The reference intervals for both cartridges, testing the 206 healthy subjects, were similar to values described in smaller studies in the literature [mean closure time (CT) 132 s for CEPI and 93 s for CADP]. The use of different lot numbers of cartridges or duplicate versus singleton testing revealed no differences. Compared with the platelet function status, the PFA-100 system had a clinical sensitivity of 94.9% and a specificity of 88.8%. For aggregometry, a sensitivity of 94.3% and a specificity of 88.3% were obtained. These values are based on all 382 specimens. A separate analysis of sensitivity by type of platelet defect, ASA use versus congenital thrombocytopathies, revealed for the PFA-100 system a 94.5% sensitivity in identifying ASA users and a 95.9% sensitivity in identifying the other defects. For aggregometry, the values were 100% for ASA users and 79.6% for congenital defects. Analysis of concordance between the PFA-100 system and aggregometry revealed no difference in clinical sensitivity and specificity between the systems (p > 0.9999). The overall agreement was 87.5%, with a Kappa index of 0.751. The two tests are thus equivalent in their ability to identify normal and abnormal platelet defects. Testing 126 subjects who took 325 mg ASA revealed that the PFA-100 system (CEPI) was able to detect 71.7% of ASA-induced defects with a positive predictive value of 97.8%. The overall clinical accuracy of the system, calculated from the area under the ROC curve, was 0.977. The data suggest that the PFA-100 system is highly accurate in discriminating normal from abnormal platelet function. The ease of operation of the instrument makes it a useful tool to use in screening patients for platelet-related hemostasis defects.

Therapeutic use of antithrombin concentrate in sepsis

Sepsis and its associated complications of disseminated intravascular coagulation (DIC) and multiple organ dysfunction syndrome (MODS) continue to be a major cause of morbidity and mortality. Improved detection of all forms of DIC is essential to assure earlier diagnosis. Studies already indicate that the therapeutic use of antithrombin (AT) concentrate may produce a more positive outcome for sepsis-associated DIC. If DIC could be identified earlier and AT concentrate could then be given earlier in the sepsis continuum, study results for the use of AT concentrate in humans might reveal a statistically significant difference versus placebo, and the efficacy of AT concentrate for this syndrome is more likely to be proved. Fixed-bolus doses of AT concentrate based on body weight are currently preferred, but improved, user-friendly assays for plasma AT levels would permit more rapid turnaround time for AT results and could help fine-tune the use of AT concentrate to the specific needs of each patient. Clinical trials involving the therapeutic use of AT concentrate in sepsis should continue, and it can be hoped that their design will reflect the concepts and conclusions offered by this panel of investigators.

Antithrombin: its physiological importance and role in DIC

Antithrombin (AT) is a single-chain glycoprotein in plasma and belongs to the family of the serpins. It is synthesized in liver parenchymal cells, and its plasma concentration is between 112-140 mg/L. AT is a unique inhibitor of the clotting system and neutralizes most of the enzymes generated during activation of the clotting cascade, especially thrombin, factors Xa and IXa. Equimolar, irreversible complexes are formed between AT and the enzymes. The interaction between AT and the activated clotting factors is at least 1,000-fold increased in the presence of heparins. Heparins bind to multiple sites of the AT molecule resulting in a steric reconfiguration. Heparins contain a specific pentasaccharide unit which is the minimum requirement for AT binding. The glycosaminoglycan (GAG) heparan sulfate found on endothelial cell surfaces also contains this pentasaccharide and can thus "activate" AT. It is believed that much of the physiological inactivation of enzymes by AT occurs on the endothelium, mediated by heparan sulfate. The binding of AT to the GAGs also releases prostacyclin which possesses strong antiinflammatory properties. Deficiencies of AT are inherited or acquired. Only acquired defects due to increased consumption are discussed, most notably AT in DIC, especially DIC in sepsis. During acute DIC, clotting factors and inhibitors are consumed faster than they can be reproduced. This consumption of AT is of great significance in DIC and sepsis, and plasma AT levels predict outcome. AT levels drop early in sepsis and laboratory signs of DIC can already be found in patients with SIRS and early sepsis. The important role of AT in DIC and sepsis is the basis for considering antithrombin concentrates as an additional therapeutic modality.

The haematological manifestations of sepsis

Haematological changes in the septic patient are, primarily, neutropenia or neutrophilia, thrombocytopenia and disseminated intravascular coagulation (DIC). Thrombocytopenia frequently arises from DIC although inhibition of thrombopoiesis or immunological platelet damage also occur. DIC contributes to bleeding and microvascular thrombosis, leading to multiple organ failure. Tissue factor release, primarily mediated by tumour necrosis factor, activates the clotting system; fibrinolysis is initially activated, but later becomes inhibited by the release of plasminogen-activator inhibitor (PAI-1), further fostering multiple organ failure. Most septic patients have compensated, chronic DIC, detectable by assays of molecular markers; the earliest signs are already found during the systemic inflammatory response syndrome. Compensated DIC later becomes decompensated with rapid consumption of factors including inhibitors such as antithrombin III (AT III) and proteins C and S. AT III concentrations of < 60-70% of the normal values predict outcome. Management of DIC must address the underlying disease, interrupt the activated haemostasis system and replace consumed coagulation constituents. Interruption of haemostasis with heparin may be attempted, but bleeding may worsen. Administration of a natural anticoagulant, such as AT III, may arrest clotting without concomitant risk of bleeding. In several animal models of DIC, AT III concentrates shortened the duration of DIC and reduced multiple organ failure and mortality. Similar benefits have been reported in early studies of patients with DIC, especially in the absence of sepsis. Studies are under way to determine whether outcome will improve if patients with sepsis are treated before the development of shock and plasma AT III concentrations are maintained at 100-150% of normal.

Plasmatische Gerinnungsstörungen bei Lebererkrankungen

Die Hämostase ist von einer normalen Funktion der Leberparenchymzellen abhängig. Fast alle Faktoren werden in diesen Zellen synthetisiert, und das retikuloendotheliale System übt eine wichtige Regulationsfunktion aus. Bei Leberzirrhosen kommt es, abhängig vom Schweregrad des Leberschadens, zum Abfall fast aller pro- und antikoagulatorischen Faktoren, das fibrinolytische System ist aktiviert, und bei schweren Leberfunktionsstörungen kommt es zur Entwicklung einer subakuten oder chronischen Verbrauchskoagulopathie und einer allgemeinen Hyperkoagulopathie. Hepatozelluläre Erkrankungen, wie leichte Hepatitiden, können ohne Hämostasestörungen verlaufen, mildere Formen gehen mit einem Abfall der Vitamin-K-abhängigen Faktoren einher. Vitamin-K-Mangelzustände zeigen lediglich verminderte Spiegel von den Faktoren, die in ihrer Synthese vom Vitamin K abhängig sind, d. h. Faktoren II, VII, IX, X, Protein C und S.

Effects of warfarin on markers of hypercoagulability in patients with heart failure

Heart failure is associated with a hypercoagulable state. A single-center, randomized, double-blind, placebo-controlled trial was performed to test the hypothesis that warfarin will modify a hypercoagulable state in heart failure. This study included 76 patients with heart failure. At baseline, patients had evidence for a hypercoagulable state with elevated plasma levels of thrombin/antithrombin III (TAT) complexes (3.4 +/- 2.0 ng/ml), prothrombin fragment F1 + 2 (1.5 +/- 0.9 nmol/L), and D-dimers (630 +/- 401 ng/ml). Warfarin therapy (international normalized ratio [INR] 2.7 +/- 1.3) significantly decreased plasma levels of TAT complexes (p < 0.002), F1 + 2 (p < 0.001), and D-dimers (p < 0.001) when compared with baseline values at 1, 2, and 3 months of therapy. In contrast, patients receiving placebo had persistent elevation of TAT complexes (p = not significant [NS]), F1 + 2 (p = NS), and D-dimers (p = NS) during follow-up at 1, 2, and 3 months. The two treatment groups followed different trends over time for all three markers (p < 0.001). The effect of low-intensity warfarin (INR 1.3 +/- 0.08) versus moderate-intensity warfarin (INR 2.3 +/- 1.1 ) on markers of hypercoagulability was evaluated in 14 patients. When compared with baseline, low-intensity warfarin administration decreased plasma levels of TAT complexes (p = NS), F1 + 2 (p = 0.05), and D-dimers (p = 0.04). In these patients F1 + 2 was further reduced with moderate-intensity warfarin (p < 0.001). Our findings suggest that a hypercoagulable state in heart failure can be modified by warfarin therapy.

In vitro platelet function in controlled ovarian hyperstimulation cycles

OBJECTIVE

To determine the effects of elevated endogenous E2 levels on in vitro platelet function in patients undergoing controlled ovarian hyperstimulation (COH).

DESIGN

Women with normal ovulatory cycles and patients undergoing COH on cycle day 3 and near ovulation (preovulatory follicles were at least 16 mm in diameter) were studied. Serum E2, Thrombostat 4000, (V. d. Goltz, Seeon, Germany), von Willebrand factor antigen (vWF-Ag), and platelet aggregation and adenosine triphosphate (ATP) release to adenosine diphosphate (ADP), collagen (COL), and arachidonic acid (AA) were measured.

SETTING

University-based outpatient infertility clinic.

PATIENT(S)

Twenty-two consenting infertile women undergoing COH cycles and 14 women with documented ovulatory cycles.

MAIN OUTCOME MEASURE(S)

Whole blood platelet aggregation with ADP, COL, AA, and Thrombostat 4000.

RESULTS(S)

Estradiol levels rose significantly at peak times (P = 0.011). No changes were noted in in vitro platelet function measured by the Thrombostat 4000 and by whole blood platelet aggregation with ADP and AA and in ATP release with ADP, COL, or AA. Aggregation with collagen was increased because of likely elevations in vWF-Ag levels.

CONCLUSION(S)

No significant changes in in vitro platelet function were noted in 19 women undergoing COH with E2 levels two to three times that observed in oral contraceptive or hormone replacement therapy users, suggesting no increased risk for arterial thromboembolism.

Antithrombin levels related to infections and outcome

Antithrombin (AT) was measured in the plasma of 59 trauma patients at Detroit Receiving Hospital from July 1987 through December 1992 to determine how well low AT levels correlated with the outcome and development of later infections. The average lowest AT measured was 74 +/- 14% (SD) (normal = 75 to 120%). The mean lowest AT of the 11 trauma patients who developed sepsis (45 +/- 13%) was significantly lower than that of the 15 who developed an infection without sepsis (66 +/- 12%) (p < 0.001) and of the 33 who did not develop an infection (87 +/- 15%) (p <0.001). No patient with an AT always > or = 70% became septic or died, and no patient with an AT always > or = 90% developed an infection. In the 33 patients who did not develop infections, the mean AT levels rose progressively from 75 +/- 17% during the first 48 hours after admission to 91 +/- 11% during the next 48 hours. In contrast, the mean AT levels in the 26 patients who later developed infections were significantly lower (48 +/- 24%) during the first 48 hours and 60 +/- 16% during the next 48 hours (p < 0.016 and p <0.001). Of 10 patients with an AT < 60% in the first 96 hours, 9 (90%) developed an infection later. Low levels of AT, thus, may be of help in predicting infection, outcome, or both in severely injured patients.

Anabolic-androgenic steroid abuse in weight lifters: evidence for activation of the hemostatic system

Anabolic-androgenic steroid abuse has recently been linked with acute vascular events in athletes. To date, the relationship between steroid abuse and the potential for cardiovascular disease has been considered almost exclusively in terms of lipid metabolism. However, recent reports of thrombosis in androgen abusing athletes with no evidence of atherosclerosis suggests the hypothesis that thrombosis risk in such athletes could be mediated through androgen induced abnormalities of coagulation. To determine if anabolic-androgenic steroid abuse in weight lifters is associated with an activation of the hemostatic system we studied forty-nine weight lifters recruited through advertisements. History of androgen use or abstinence was confirmed via urine assays. Plasma was assayed for clotting and fibrinolytic activity by measuring thrombin/antithrombin complexes (TAT), prothrombin fragment 1 + 1 (F1 + 2), and D-dimers (D-di); markers of the endothelial based fibrinolytic components were assayed by measuring tissue plasminogen activator antigen (t-PA Ag) and its inhibitor (PAI-1); finally, the activity of antithrombin III, protein C, and protein S were measured. Abnormally high concentrations of TAT complexes were noted in 16% of our confirmed steroid using weight lifters compared to 6% of our confirmed nonusers (P = .01). Steroid users also demonstrated abnormally high concentrations of F1 + 2 and D-dimers when compared to nonusers (44 vs. 24%, P < .001, and 9 vs. 0%, respectively). Non-steroid users were more likely to have elevated levels of t-PA Ag and PAI-1 than our steroid using weight lifters (both P < .001). The activities of antithrombin III and protein S were more likely to be higher in users compared to nonusers (22 vs. 6%, P = .005; 19 vs. 0%, respectively). Some anabolic-androgenic steroid using weight lifters have an accelerated activation of their hemostatic system as evidence by increased generation of both thrombin and plasmin. These changes could reflect a thrombotic diatheses that may contribute to vascular occlusion reported in young athletes using these drugs. The predictive value of these coagulation abnormalities in terms of risk of thrombosis to individual steroid using weight lifters or the population as a whole remains to be studied.

Performance characteristics and clinical evaluation of an in vitro bleeding time device--Thrombostat 4000

The performance characteristics of an in vitro bleeding time device--Thrombostat 4000 were evaluated and compared with the Simplate bleeding time in healthy individuals and patients with disorders of primary hemostasis. Reference ranges were established using 30 normal volunteers. Although there were variations between different filter batches, reproducibility was good within a single batch. There were no differences between the two channels of the instrument and between male and female subjects. Hematocrit correlated negatively with the initial flow (IF) and IF correlated positively with closure time (T) and bleeding volume (V). Aspirin could be detected only when the traditional addition of ADP was replaced with CaCl2. Both, closure time (T) or bleeding volume (V) were more sensitive than Simplate bleeding time and T was more sensitive than V in detecting patients with disorders of primary hemostasis. We conclude that the Thrombostat 4000 is a reproducible, reliable, sensitive and easy to use instrument. It is superior to the traditional in vivo bleeding times for investigations of disorders of primary hemostasis (screening, diagnosis, monitoring, etc.).

Clinical experience with the Thrombostat 4000

Bleeding times are presently widely used to screen patients with primary hemostasis defects although their accuracy and reliability has been questioned by many investigators. Platelet aggregation studies are not suited for routine use. We investigated the performance characteristics of the Thrombostat 4000, a device that assesses primary hemostasis. Tests can be performed by adding ADP, epinephrine, CaCl2 or NaCl to the collagen onto which platelets adhere. It was found, using normal volunteers and patients, that ADP and epinephrine had acceptable reference ranges with coefficients of variance between 9-12% for within run and between runs. However, major differences were seen when different filter badges were used--a reflection of differences in collagen. Regular citrated blood, routinely drawn for coagulation studies, can be used; test performance can be delayed for up to five hours when the blood is kept at room temperature. The effects of aspirin on volunteers could be detected when epinephrine was used, but not with ADP. ADP addition allowed the detection of more patients with primary hemostasis defects than bleeding times, and epinephrine was as useful as ADP in detecting these abnormalities. The data suggest that the broadest spectrum of platelet defects (ASA use and platelet dysfunction) can be detected with epinephrine. Inconsistencies in collagen used for coating of the filters is a major drawback for the routine use of this device in screening primary hemostasis defects.

Preliminary data from a field trial of the PFA-100 system

The PFA-100 system (Dade International Inc., Miami, FL) is a platelet function analyzer, the design of which is based on the technology of the Thrombostat 4000 VDG, Seeon, Germany. It was developed to measure primary, platelet dependent hemostasis in citrated whole blood in vitro. A first pilot study was conducted with the instrument to assess performance characteristics. Healthy subjects (normals) who had not ingested any medications, and patients (abnormals) with primary, platelet-related hemostasis defects, which included users of aspirin, were studied with two test cartridges; collagen/ADP and collagen/epinephrine. Before the study certain variables were tested that ascertained that blood drawn into either 3.8% or 3.2% sodium citrate containing vacutainers (rather than syringes) could be used for testing. Tests must be performed within a five-hour time span from drawing to testing, and blood must be kept at room temperature. Normal reference values were 77-133 seconds closure times for collagen/ADP and 98-185 seconds for collagen/epinephrine. Precision testing revealed a CV of < 10% for within-day and between-day (five days) analyses on collagen/ADP cartridges and a CV of 5-14% for both runs on the collagen/epinephrine cartridges. No clinically important differences were found between measurements in the two positions of the instrument, although one follows the other.(ABSTRACT TRUNCATED AT 250 WORDS)

Coagulopathies of liver disease

Disturbed liver parenchymal cell function adversely impacts on the hemostasis system, the extent of which correlates with the degree of liver disease. Because liver parenchymal cells synthesize most factors of the clotting and the fibrinolytic systems, levels of these procoagulant and anticoagulant as well as profibrinolytic and antifibrinolytic factors will decrease in plasma. These changes may be minor in patients with mild liver disease but are severe in patients with cirrhosis. Thrombocytopenia and thrombocytopathy usually complicate the clinical presentation, and systemic activation of the fibrinolytic system is always seen in cirrhotic individuals. Whether this fibrinolytic activation is primary or secondary in response to DIC is controversial. Some of the laboratory findings in DIC may be a reflection of decreased hepatic clearance of activation products by the reticuloendothelial system of the diseased liver. In patients with vitamin K deficiency or in those receiving oral anticoagulants, only the vitamin K-dependent procoagulants and anticoagulants are altered; all other parameters remain in the normal range. Laboratory changes associated with various surgical interventions involving the liver depend on the underlying pathology. Severe hemorrhages are encountered during orthotopic liver transplantation. During the anhepatic phase and during the reperfusion phase, there is a major activation of the fibrinolytic system. It is unclear whether this fibrinolytic response is primary or secondary. The use of antifibrinolytic agents has markedly reduced the clinical bleeding and, thus, the requirement for blood and blood products. Bleeding associated with partial liver resection is usually mechanical in nature, but peritoneovenous shunt operations can result in DIC. Ascites fluid is the trigger. The injection of thrombin containing sclerosants can also activate the hemostasis system in vivo, although, generally, no clinically detectable adverse reactions are noted.

Prothrombin fragment F 1 + 2 and oral anticoagulant therapy

This study was undertaken to establish a correlation between prothrombin activation fragment F 1 + 2 and one-stage prothrombin time (PT) ratios in patients receiving oral anticoagulant therapy. One hundred consecutive patients on warfarin treatment were utilized for this study. The patients had received warfarin for not less than four days prior to entry into the study. F 1 + 2 levels and PT ratios were found to be 0.28 +/- 0.24 nM/L (mean +/- SD) ranging from 0.01 to 1.5 nM/L and 1.62 +/- 0.46 (mean +/- SD) ranging from 0.97 to 3.11, respectively. Most patients on oral anticoagulants with PT ratios between 1.2 - 1.7 exhibited decreased concentrations of F 1 + 2. Normal control values of F 1 + 2 were established for this study in 40 healthy individuals; they were 0.40 +/- 0.23 nM/L (median +/- SD) ranging from 0.11 to 1.19 nM/L. Mean plasma levels of F 1 + 2 were significantly lower in the anticoagulated patients as compared to the healthy controls (t = 2.377, p < 0.05). The relationship between F 1 + 2 levels and PT ratios in the 100 anticoagulated patients was analyzed by linear regression. No significant correlation (r = -0.208) was found between F 1 + 2 levels and PT ratios. It is concluded that the degree of reduction in F 1 + 2 levels is not proportional to the intensity of therapy reflected by the PT ratios in anticoagulated patients.

Hemostasis and diagnosis of preeclampsia

The diagnosis of preeclampsia, with all of its consequences, is at times difficult to establish, especially when the patient has underlying chronic hypertension and is not known from prior prenatal care visits. Many screening tests have been proposed. These should be sensitive, relatively specific, easy to perform, of low cost, and have a reasonable interval from prediction to disease onset. Laboratory assays would obviously be useful. We evaluated hemostasis tests for the diagnosis of preeclampsia, and compared fibronectin, antithrombin III and alpha 2-antiplasmin in 48 preeclamptics and 86 control nulliparas. Receive operator characteristic (ROC) curve analysis suggested that fibronectin is the most effective of these tests. A similar analysis comparing the results of previous studies using serum iron, angiotensin infusion, urinary calcium/creatinine ratio, the rollover test and uric acid suggested a possible role for fibronectin in the diagnosis of preeclampsia. While not ideal, there seems to be, at present, no other, easy to perform laboratory test that outperforms fibronectin in predicting preeclampsia.

Coagulation defects in liver disease

A normally functioning hemostasis system is closely related to liver function. The liver parenchymal cells produce most of the factors and inhibitors of the clotting and fibrinolytic systems, and the RES of the liver greatly aids in the clearance of activation products. Hemostasis defects thus depend on the extent of liver damage. A wide spectrum of defects is found in patients with liver cirrhosis. Owing to impaired protein synthesis, most factors and inhibitors of the clotting and the fibrinolytic systems are markedly reduced. Additionally, abnormal vitamin K-dependent factor and fibrinogen molecules have been encountered. Most patients have hyperfibrinolysis that could be DIC in nature. Thrombocytopenia and thrombocytopathy are also found. Acute or chronic hepatocellular disease may display decreased vitamin K-dependent factor levels, especially factor VII and protein C, with other factors still being normal. If patients go into hepatic failure, the abnormalities resemble those found in liver cirrhosis. Vitamin K deficiency is associated with the production of poorly functioning vitamin K-dependent factors. All other hemostasis parameters are normal. Disturbances associated with liver surgeries again depend on the underlying liver problem. Peritoneovenous shunts (LeVeen) may lead to DIC; bleeding from partially resected liver surfaces is usually a mechanical problem. Severe bleeding is encountered with orthotopic liver transplantation. It is greatly influenced by the activation of the fibrinolytic system. This occurs during the anhepatic phase and during the reperfusion phase. The hyperfibrinolysis is mediated by an intense release of t-PA. Antifibrinolytic drugs, if used cautiously, have markedly reduced bleeding and thus reduced need for blood and blood product substitution.

Fibrinolytic parameters in women undergoing ovulation induction

OBJECTIVE

The purpose of this study was to evaluate the effect of elevated levels of circulating estradiol on the clotting and fibrinolytic system in patients undergoing controlled ovarian hyperstimulation.

STUDY DESIGN

Fifty-two patients undergoing controlled ovarian hyperstimulation with human menopausal gonadotropins or urofollotropin were asked to participate. Blood for hemostasis parameters was obtained on the days that patients returned for estradiol sampling. Sample days were identified as cycle days 1 to 5 (baseline), 6 to 9, and 10 to 14. Each factor was analyzed by repeated-measures analysis of variance and correlation analysis.

RESULTS

A significant decline was observed for tissue plasminogen activator antigen and plasminogen activator inhibitor type 1 activity from baseline to cycle days 10 to 14. As serum estradiol levels increased throughout each phase (maximum mean estradiol 739.8 pg/ml), a significant linear decrease was observed for both tissue plasminogen activator antigen and plasminogen activator inhibitor type 1 activity, whereas thrombin-antithrombin III complexes did not change significantly. A significant positive correlation was also observed for plasminogen activator inhibitor activity and tissue plasminogen activator antigen level over all cycle days examined.

CONCLUSION

Down-regulation of the fibrinolytic system was observed as estradiol levels increased. However, thrombin formation did not change, thus suggesting that elevated circulating estradiol alone does not predispose to a thromboembolic event.

Thrombosis and hormone replacement therapy in postmenopausal women

OBJECTIVE

The effects of postmenopausal hormone replacement therapy on thrombosis remain controversial. We tested the hypothesis that estrogen or progesterone has no significant effect on thrombosis by means of newly developed markers of blood clotting, specifically prothrombin fragment 1 + 2, a marker of factor Xa generation, and thrombin-antithrombin III complex, a marker of thrombin generation.

STUDY DESIGN

A prospective study that included 106 women, 68 postmenopausal women on hormone replacement therapy and 38 postmenopausal controls, was performed. Plasma levels of prothrombin fragment 1 + 2 and thrombin-antithrombin III complex were measured by enzyme-linked immunosorbent assay. Multivariate analysis of the covariance was used for statistical analysis, controlling for patient's age because the hormone replacement therapy group was older.

RESULTS

There were no statistically significant differences between the hormone replacement therapy and control groups in either of the clotting parameters measured. A comparison of the levels of prothrombin fragment 1 + 2 and thrombin-antithrombin III complex in patients receiving estrogen alone or estrogen plus progestin also revealed no differences.

CONCLUSIONS

Current doses of postmenopausal hormone replacement therapy do not appear to enhance in vivo clotting. Thromboembolic complications among postmenopausal women receiving hormone replacement therapy may therefore be secondary to congenital or other acquired coagulation defects.

Alpha 2-antiplasmin deficiency. An overlooked cause of hemorrhage

PURPOSE

Alpha 2-Antiplasmin (AP) deficiency is a rare congenital bleeding disorder that presents with normal screening tests for platelet function and clotting. We believe that this disorder is frequently overlooked, especially in women with unexplained bleeding.

PATIENTS AND METHODS

We report on two families and one single patient with heterozygous AP deficiency.

RESULTS

All patients and most relatives with the defect had a mild bleeding tendency.

CONCLUSIONS

We suggest the incorporation of the AP assay in all patients who have a bleeding disorder with normal platelet studies and normal clotting profiles.

Thrombin increases the metastatic potential of tumor cells

Initial arrest of tumor cells in the microvasculature and their attachment to the endothelium and subendothelial matrix (SEM) are essential prerequisites for metastasis to occur. Factors mediating these interactions are viewed as important determinants of the tumor-cell metastatic phenotype. In this work we have studied the effects of thrombin, its analogs and its precursors on the adhesive properties and metastatic potential of tumor cells. We show that alpha-thrombin, the native form of the key coagulation enzyme, is capable of enhancing tumor-cell adhesion to both the endothelium and SEM components represented by fibronectin. Subclotting, physiological concentrations of alpha-thrombin produced a 2- to 5-fold increase in tumor-cell adhesion. A bell-shaped dose-response curve was observed, with maximal effect at 0.1 U/ml. Maximum effect occurred when cells were exposed to the agonist for 15 min and exposure for up to 4 hr resulted in enhanced tumor-cell adhesion. Prolonged incubation with thrombin resulted in a decline in the thrombin-enhanced adhesion which reached unstimulated control levels by 24 hr. Thrombin precursors and active-site-inhibited thrombin analogs only had minimal adhesion-enhancing activity; nitro- and exosite-alpha-thrombin, which retain a functional active site, mimicked, although to a lesser degree, the action of alpha-thrombin. Tumor-cell incubation with thrombin resulted in an upregulated cell-surface expression of the alpha11b beta 3 integrin, a receptor mediating interactions between tumor cells and endothelial cells, and between tumor cells and SEM. Antibodies against alpha 11b beta 3 integrin effectively inhibited thrombin-enhanced tumor-cell adhesion. Thrombin effects on tumor cells involved the PKC signal transduction pathway as thrombin-enhanced adhesion was inhibited by pre-incubation with PKC inhibitors and a transient PKC translocation from cytosol to membrane was observed following thrombin challenge. In vivo, thrombin-treated tumor cells demonstrated a 2-fold increase in their lung-colonizing ability. In contrast to the adhesion results, the metastasis-enhancing effects of alpha-thrombin were mimicked by a thrombin precursor (prothrombin) and thrombin analogs.

Amniotic fluid platelet factor 4 and beta-thromboglobulin as markers of structural abnormalities

Platelet factor 4 (PF4) and beta-thromboglobulin (BTG) are unique markers of irreversible platelet activation. We measured PF4 and BTG in amniotic fluid from 102 genetic amniocenteses, in which 78 had normal amniotic fluid alpha-fetoprotein (AFP) levels with normal pregnancies, and 24 had high amniotic fluid AFP levels with abnormal pregnancies. PF4 and BTG were significantly higher in the abnormal pregnancy/elevated amniotic fluid AFP group (p < 0.002 in each case) and correlated with AFP expressed as multiples of the median (p < 0.05 and p < 0.0001, respectively). Our results are compatible with passage of PF4 and BTG across fetal membranes and/or enhanced fetal platelet activation in fetuses with structural anomalies and elevated AFP.

Amniotic fluid platelet factor 4 and beta-thromboglobulin

Platelet activating factor (PAF), a powerful platelet activator, has been identified in human embryos and fetuses, and may induce fetal lung maturation. The potential effect of PAF on fetal platelets as indicated by release of beta-thromboglobulin (BTG) and platelet factor 4 (PF4) has not been investigated. We measured BTG and PF4 in amniotic fluid from 78 genetic and 35 pulmonary maturity amniocenteses. BTG and PF4 were higher in the genetic amniocentesis samples (p < 0.001 in each case) than in the lung maturity samples. BTG and PF4 did not correlate with the pulmonary maturity parameters as measured by the lecithin to sphingomyelin ratio and phosphatidylglycerol concentration. Our findings suggest a fetal origin of BTG and PF4 in amniotic fluid.

Determination of low-molecular-weight heparin by Heptest on the automated coagulation laboratory system

The manual Heptest for measuring low-molecular-weight heparin fractions was applied to a fully automated, coagulation-dedicated analyzer, the Automated Coagulation Laboratory 300 Plus. The clot-based assay mode of the instrument was used, which operates on the principle of light scattering. Undiluted plasmas and the original reagents of the Heptest kit were used. Also, the 2-minute incubation time of the manual procedure was maintained. Automation reduced plasma and reagent volumes by about one half. As a result of the high precision of the automated procedure, single determinations suffice, and 18 plasma samples can be analyzed in about 8 minutes. Coefficients of variation were 1.0% to 3.2% for within-run and 1.9% to 6.0% for inter-run analyses. Analytical recovery was 98% to 104%. Comparisons of 132 samples between the two procedures yielded an R value of 0.974 for activity expression in seconds and 0.945 for U/mL. Several low-molecular-weight heparin fractions were tested.

Perspectives for the future

The pathophysiology of sepsis and septic shock is extremely complex and ultimately involves every physiological pathway. The initiating event is the entrance of endotoxin or similar substances into the blood which initiates the release of multiple mediators. These are designed to react locally and to protect the organism. Their constant release, however, sets in motion up- and down regulations, ultimately resulting in "metabolic anarchy". Tumor necrosis factor alpha and other cytokines trigger several systems, especially coagulation to yield DIC, and the complement system. Many treatment modalities have been developed, most recently those which substitute inhibitors of various systems. Antithrombin III concentrates and potentially protein C concentrates are designed to arrest DIC. C1-esterase inhibitor concentrates should intercept the activation of the complement system and the contact phase of coagulation and its relationship to kinin generation. Even newer approaches entail antibodies to tumor necrosis factor alpha or endotoxin itself. The complex process of sepsis will undoubtedly require a multifaceted therapeutic approach.

Pathogenesis of venous thrombosis

This brief review attempts to describe the present understanding of the pathogenesis of venous thrombosis in general with special reference to venous thromboembolism in spinal cord injury patients with paralysis. The component parts of Virchow's triad are examined. Most venous thrombi seem to originate in regions of slow blood flow, ie, the large venous sinuses of the calf and thigh or in valve cusp pockets. Decreased blood flow or even stasis due to lack of the pumping action of the large muscle packages in paralyzed patients is undoubtedly one of the major factors. As blood pools, activation products of the coagulation system accumulate locally leading potentially to local hypercoagulability. Activation products of clotting and fibrinolysis can induce endothelial damage which in turn leads to further activation of the hemostasis system. Endothelial damage may also result from distension of the vessel walls by the pooling blood. Blood flow is further decreased by hyperviscosity due to elevated fibrinogen levels and dehydration. Some spinal cord injury patients may sustain direct trauma to the legs; others may encounter vessel wall damage by the immobilized limbs. Shortly after injury, certain changes develop in the clotting system, especially increases in components of the von Willebrand factor macromolecular complex and increased platelet aggregability which could further contribute to hypercoagulability. Recently, an inhibition of the fibrinolytic system was suggested which also could add to a prothrombotic state. All of these interrelated processes clearly explain the high risk of venous thromboembolism in spinal cord injury patients with paralysis which has been clearly demonstrated by many investigators. It is hoped that intense thrombosis prophylaxis will reduce the incidence of this potentially devastating complication.

Coagulation abnormalities in liver disease

Hemostasis is intimately related to liver function, because most coagulation factors are synthesized by liver parenchymal cells and the liver's reticuloendothelial system serves an important role in the clearance of activation products. The extent of coagulation abnormalities depends upon the degree of disturbed liver function. Acute or chronic hepatocellular diseases may display decreases in the vitamin K-dependent factors (prothrombin; factors VII, IX, and X; proteins C and S), whereas other parameters remain normal. Patients with hepatic failure may present with the entire spectrum of factor deficiencies and may even develop disseminated intravascular coagulation (DIC). Patients with liver cirrhosis have a wide spectrum of abnormalities. Except for factor VIII:C and von Willebrand factor, all procoagulant and inhibitory factors are decreased, which is a reflection of impaired protein synthesis. Abnormal fibrinogen and prothrombin molecules can be identified. Platelets are quantitatively and qualitatively altered, and most patients develop DIC. Vitamin K deficiency leads to the production of abnormal vitamin K-dependent factors. The factors lack gamma-carboxy glutamic acid residues in the NH2-terminal part of their molecules. Surgery associated with the liver leads to major hemostasis alterations. The LeVeen shunt is invariably related to DIC. Bleeding with partial liver resection is mostly mechanically induced, but chronic DIC may be present. Orthotoptic liver transplantation is associated with severe hemorrhages. These are partly due to the pre-existing hemostasis defects and partly due to DIC with a marked fibrinolytic response. This is especially noted during the anhepatic phase and when the donor liver is perfused by the recipient's blood. Postoperative recovery is quick, provided the graft is not rejected. Postoperatively, there may be an initial hypercoagulable state, which could be related to the thrombosis occasionally encountered.

Thrombosis in spinal cord injury

Some traditional coagulation assays and several new molecular markers of hemostatic activation were measured in 37 patients with spinal cord injury (SCI). Twenty one of the patients (57%) developed deep vein thrombosis (DVT). The radiofibrinogen uptake test (RFUT) was used to diagnose DVT. Thirty eight percent of quadriplegic and 88% of paraplegic patients developed DVT (p < 0.005). No significant differences were found in platelet counts, mean platelet volumes, fibrinogen levels, von Willebrand factor (Ag) levels, platelet factor 4 and beta thromboglobulin concentrations between the groups with and without DVT. Fibrinopeptide A, thrombin/antithrombin III (TAT) complexes and plasma D-dimer levels were significantly higher in the patients with thrombosis. Most patients with DVT had elevated TAT complex levels up to three days before the RFUT became positive. D-dimer levels were highest after the diagnosis had been made.

An in vitro evaluation of the effect of laser irradiation on the thrombogenicity of thrombus

The effect of laser irradiation on the thrombogenicity of thrombus was evaluated by treating thrombi, formed in-vitro from canine blood, with two different doses of cw Nd:YAG laser energy at 1064 nm. The thrombi were then incubated with whole blood, and the plasma levels of fibrinogen and thrombin-antithrombin III-complexes were measured. A statistically significant decrease (p < 0.05) in the thrombogenicity was indicated by a reduction in both fibrinogen consumption and levels of thrombin-antithrombin III-complexes in the high dose group (600 joules, 100 degrees C peak temperature) in comparison to the low dose group (300 joules, 70 degrees C peak temperature) and the untreated thrombi. These findings suggest that laser irradiation of thrombus at an appropriate dose may substantially reduce its thrombogenicity and ability to modulate hemostasis.

Markers for endothelial injury, clotting and platelet activation in preeclampsia

The etiology of disseminated intravascular coagulation (DIC) in preeclampsia is not well understood. We measured plasma levels of fibronectin (FN), which may reflect endothelial cell injury, fibrinopeptide A (FPA), a specific marker of clotting, platelet counts (PLC) and mean platelet volumes (MPV), as well as beta-thromboglobulin (beta TG) and platelet factor 4 (Pf4), products of irreversible platelet activation in 24 preeclamptic patients and 24 controls matched for age, gestational age, labor status, and parity. In preeclampsia, FN and FPA were significantly elevated while PLC were significantly decreased (P less than 0.0001, less than 0.05 and less than 0.01, respectively). beta TG, Pf4, and MPV values did not show significant differences. These findings support the hypothesis that endothelial injury, clotting activation and platelet consumption are increased in preeclampsia. However, the much closer association of preeclampsia with FN levels as compared to FPA, beta TG, Pf4, suggests that endothelial injury is a more basic mechanism of preeclampsia than clotting or platelet activation.

LMW heparin (anti-Xa) assays for clinical monitoring and pharmacokinetic studies on the automated coagulation laboratory (ACL)

Chromogenic anti-Xa activity procedures were developed for monitoring LMW heparins on the Automated Coagulation Laboratory 300 Plus (ACL, Instrumentation Laboratory) system. For daily monitoring, a "Routine" procedure was devised which allows accurate measurements between plasma levels of 0.1 and 1.0 u/ml LMW heparin. For lower levels a "Routine-Low" method was developed which assesses activities between 0.05 and 0.4 u/ml. Due to variabilities in dODs of individual baseline plasmas, levels below 0.05 u/ml might be inaccurate when pooled normal plasma is used to establish the reference curve. While levels less than 0.05 u/ml should rarely be encountered when monitoring LMW heparins for routine clinical use, pharmacokinetic studies require accurate measurements below that level. For this reason a "Research-High" and a "Research-Low" procedure was designed. For these procedures a study subject's own baseline plasma was used to establish the reference curve. The "Research-High" measures activities between 0.4 and 2.0 u/ml, the "Research-Low" between zero and 0.4 u/ml. The procedures have excellent within-run and inter-run coefficients of variation (less than 5%) and high levels of accuracies. Even inter-instrumental reproducibilities are less than 10%. Different manufacturers' LMW heparins can be analyzed by these assays. The procedures offer full automation, great cost-effectiveness due to lower reagent volumes, rapid turn-around time and great accuracy and reproducibility.

Circadian variation in platelet function in healthy volunteers

Circadian variation in hemostatic factors may contribute to a higher frequency of cardiac events observed in the morning and with activity. Diurnal changes in these factors were investigated by measuring in vitro platelet aggregability in response to epinephrine and adenosine diphosphate together with beta-thromboglobulin and platelet factor 4 as indexes of in vivo platelet activation. Activation of coagulation was measured by thrombin-antithrombin III complexes and D-Dimers. Tests were performed in 9 normal healthy subjects. Circadian changes occurred in beta-thromboglobulin (p less than 0.05) and platelet factor 4 (p less than 0.06). Plasma levels of beta-thromboglobulin and platelet factor 4 were lowest with patients supine and resting at 7 and 8 A.M., and increased with activity, with peak levels achieved at 3 P.M. (p less than 0.01). Thrombin-antithrombin III complexes (p = 0.44), D-Dimer (p = 0.36) and in vitro platelet aggregability to adenosine diphosphate (p = 0.20) did not show diurnal variation. There was a trend toward circadian variation in vitro platelet aggregability to epinephrine, but these changes did not achieve statistical significance (p = 0.16). Circadian changes of in vivo release of beta-thromboglobulin and platelet factor 4 correlated to patient activity and not to the morning peaks in ischemic events. These data indicate that changes in platelet function and not in coagulation have a diurnal occurrence.