Protein C Levels Research Articles

Antithrombotic effects of thrombin-induced activation of endogenous protein C in primates.

The effects on thrombosis and hemostasis of thrombin-induced activation of endogenous protein C (PC) were evaluated in baboons. Thrombosis was induced by placing into arteriovenous shunts a segment of Dacron vascular graft, which generated arterial platelet-rich thrombus, followed by an expansion region of low-shear blood flow, which in turn accumulated fibrin-rich venous-type thrombus. Thrombosis was quantified by 111In-platelet imaging and 125I-fibrinogen accumulation. Intravenous infusion of alpha-thrombin, 1-2 U/kg-min for 1 h, increased baseline activated PC levels (approximately 5 ng/ml) to 250-500 ng/ml (P < 0.01). The lower thrombin dose, which did not deplete circulating platelets, fibrinogen, or PC, reduced arterial graft platelet deposition by 48% (P < 0.05), and platelet and fibrin incorporation into venous-type thrombus by > 85% (P < 0.01). Thrombin infusion prolonged the activated partial thromboplastin clotting time, elevated fibrinopeptide A (FPA), thrombin-antithrombin III complex (T:AT III), and fibrin D-dimer plasma levels (P < 0.01), but did not affect bleeding times. Thrombin's antithrombotic effects were blocked by infusing a monoclonal antibody (HPC-4) which prevented PC activation in vivo, caused shunt occlusion, increased the consumption of platelets and fibrinogen, elevated plasma FPA and T:AT III levels, and reduced factor VIII (but not factor V) procoagulant activity (P < 0.05). We conclude that activated PC is a physiologic inhibitor of thrombosis, and that activation of endogenous PC may represent a novel and effective antithrombotic strategy.

Anticoagulant properties of the endothelium studied by the standard venous occlusion test

Venous occlusion (VO) during which thrombin (Th) is postulated to be generated is routinely used for evaluation of fibrinolytic potential of endothelium (E). This study was performed to find out whether VO can also be used for assessment of anticoagulant function of E. VO was performed in 98 male patients (pts) with ischemic heart disease. Levels of protein C (PrC) which is related to Th binding by thrombomodulin and fibrinopeptide A (FpA)--a marker of presence of free Th--were determined together with some other factors of coagulation and fibrinolysis. Differences between pre- and postVO PrC levels fluctuated from -54.8% to +57.3%. According to reaction of PrC to VO pts were divided into 2 groups: 13 pts with increase or no change and 17 pts with decrease (consumption) of PrC. In pts without PrC consumption there was a significant increase in FpA. In pts with PrC consumption FpA was unchanged. In pts with PrC consumption exceeding its median value for this group (14%) PAI-1 antigen level fell significantly (-8.4 + 4%) during VO. Thus PrC consumption after VO indicates that TH is effectively removed from blood stream by endothelial factors. Absence of consumption of PrC is a sign of ineffective anticoagulant function of E. Increase in PrC level during VO in some pts may be due to its escape from tissue depot.

Protein C and S deficiency in severe infectious purpura of children: a collaborative study of 40 cases.

We studied, in 40 children (mean age: 52 months) with severe infectious purpura, the relationships between protein C (PC) and protein S (PS) levels, and shock, disseminated intravascular coagulation (DIC) and outcome. We determined, on admission, PC antigen (ELISA) and activity (chromogenic test), and total PS (ELISA). Results were expressed as % of normal adult values. Statistical analysis was performed with SAS. Thirty children were in shock, 20 had DIC. All children with DIC, and 10 without DIC were in shock. Of 20 children who were in shock and had DIC, 7 died and 3 had an amputation. PC antigen was significantly decreased in shock children (p less than 0.05), in children with DIC (p less than 0.0005), and in non-survivors (p less than 0.05). PC activity was significantly decreased in shock children (p less than 0.05), in children with DIC (p less than 0.0005), and in non-survivors (p less than 0.005). Total PS was not decreased in shock children, but was significantly decreased in children with DIC (p less than 0.005), and in non-survivors (p less than 0.005). We conclude that PC and PS levels were decreased in our children, and that PC levels were significantly decreased in the presence of shock, DIC, and fatal outcome. PC and antithrombin III (AT III) supplementation, should be evaluated in children with severe infectious purpura with shock and DIC.

Septic Shock, Multiple Organ Failure, and Disseminated Intravascular Coagulation: Compared Patterns of Antithrombin III, Protein C, and Protein S Deficiencies

Our aim was to document the following in patients with septic shock and disseminated intravascular coagulation (DIC): (1) the influence of DIC in the mortality rate and the occurrence of organ failure; (2) the comparative prognostic value of initial antithrombin III (ATIII), protein C (PC), and protein S (PS) levels; and (3) the compared pattern of sequential ATIII, PC, and PS levels according to clinical outcome. Demographic data, criteria of severity, mortality in ICU, frequency of organ failure, hemodynamic and oxygenation parameters, and laboratory findings were compared in patients with septic shock according to the occurrence of DIC. Initial and sequential levels of ATIII (activity), PC (antigen and activity), PS (total and free), and C4b binding protein (C4bBP) were compared according to the outcome in patients with DIC. Sixty patients with septic shock were studied. Forty-four entered the group DIC+; 16 entered the group DIC-. Simplified acute physiologic score (SAPS), frequency of acquired organ failure, blood lactate, and transaminase values were significantly higher in the group DIC+. The mortality rate reached 77 percent in group DIC+ vs 32 percent in DIC- (p less than 0.001). In patients with DIC, a fatal outcome was associated with higher bilirubin and transaminase levels, lower PaO2/FIo2 ratio, Vo2, Do2 and O2 extraction. In the group DIC+, all patients but two had severe deficiencies in ATIII and PC levels. Significant correlations were found between initial ATIII and PC levels, PC and free PS levels, and free PS and C4bBP levels. Initial ATIII levels had the best prognostic value for prediction of subsequent death. Serial measurements were consistent with a prolonged ATIII and PC deficiency with significantly different levels between survivors and nonsurvivors. DIC is a strong predictor of death and multiple organ failure in patients with septic shock. Sequential ATIII, PC, and PS measurements were consistent with prolonged consumption or inhibition that might account for a sustained procoagulant state and inhibition of fibrinolysis. The initial ATIII level was the best laboratory predictor of death in these patients.

A continuous spectrum of hypercoagulability exists in acute nonlymphoblastic leukemia.

A consumption coagulopathy syndrome has frequently been reported in association with some cases of acute nonlymphoblastic leukemia (ANLL) and mainly in acute promyelocytic leukemia (M3). Eighteen cases of ANLL have been studied on admission, before chemotherapy was started. Levels of antithrombin III (AT-III), protein C (PC), protein S (PS), thrombin-antithrombin complex (T-AT-III), tissue plasminogen activator, plasminogen (Pg), alpha-2-antiplasmin (alpha-2-AP), D-dimer (DD) and fibrinogen (Fg) were determined. The results showed normal levels of AT-III and PS, decreased levels of PC, alpha-2-AP, Pg and Fg in some cases, and an elevation of DD and T-AT III complex in almost all patients. There was a continuous evolution of data from M1 cases in which only slight alterations were seen up to M3 cases where all those pathologic data were observed.

Activation of the host response in human plasmodium falciparum malaria: Relation of parasitemia to tumor necrosis factor/cachectin, thrombin-antithrombin III, and protein C levels

purpose: Hemostatic alterations and elevated tumor necrosis factor/cachectin (TNFα) serum levels may contribute to the pathogenesis of organ complications in human Plasmodium falciparum malaria. Therefore, we examined whether altered protein C (PC) and thrombin-antithrombin III (TAT) plasma levels correlated with TNFα serum concentrations, parasitemia, and the clinical course of human P. falciparum malaria. patients and methods: Forty-seven patients with P. falciparum malaria were evaluated prospectively before and during antiparasitic therapy. TNFα serum levels were determined by immunoradiometric assay, PC and TAT plasma antigen by enzyme-linked immunosorbent assay, and PC and PC inhibitor-1 (PCI-1) activity levels by functional tests. Cultured endothelial cells were incubated with serum from four patients with malaria and from healthy control subjects and then assayed for procoagulant activity. Northern blot hybridization was used to detect tissue factor mRNA. results: In vivo, TNFα serum concentrations were elevated (median: 38.6 pg/mL; n =47) while plasma levels of PC (antigen 55.4%; activity 39.0%; n = 47) and PCI-1 (0.56 U/L) were decreased in almost all patients before antiparasitic treatment. At the same time, TAT concentrations were high. These alterations correlated significantly (p <0.01) both with the severity of the disease (as defined by organ impairment) and with the number of circulating parasitized erythrocytes. Low PCI-1 activity correlated with low PC activity (p <0.001) and antigen (p <0.05) levels. The plasma level of coagulation factor IX, another vitamin K-dependent protein, was not significantly changed. In vitro, incubation of endothelial cells with patient serum (severe P. falciparum malaria) increased both endothelial cell procoagulant activity and cytoplasmic tissue factor mRNA levels. conclusion: Elevated levels of TNFα and TAT, decreased plasma levels of anticoagulant PC, and the induction of procoagulant activity in endothelial cells by patient serum indicate a shift in the balance of hemostatic activity towards a precoagulant state in P. falciparum malaria. The alterations in TNFα, TAT, and PC levels may be a response to infection, since they correlate with parasitemia and are reversed during antiparasitic treatment.

Effect of Hemodialysis on Protein C, Protein S, and Antithrombin III Levels

We studied the effect of hemodialysis on natural coagulation inhibitors including protein C (PC), protein S (PS), and antithrombin III (AT III), as well as the correlations between the antigen level (immunological activity) and functional activity of individual coagulation inhibitor. Plasma AT III, PS, and PC were measured in 20 uremic patients on maintenance hemodialysis immediately before, during, and after dialysis treatment. These values were compared with those obtained from 20 matched healthy controls. Plasma PC and total PS antigen levels were measured by enzyme immunoassay. The plasma AT III antigen level was determined by Laurell rocket immunoelectrophoresis. Functional activities of PC and AT III were determined by the amidolytic method. Free PS antigen level was quantitated by measuring the free PS-related antigen after the sample was treated with polyethylene glycol to remove the C4b-binding protein. Uremic patients on maintenance hemodialysis had a higher total PS antigen level, but a lower free PS antigen level compared with the controls. Both the antigen level and functional activity of AT III in uremic patients were significantly lower than those of controls. Their predialysis plasma PC antigen level and functional activity were not different from those of normal controls. A significant correlation between the antigen level and functional activity of PC, PS, and AT III was demonstrated in healthy controls, but not in hemodialysis patients. No significant change in the level of AT III or PS was observed with hemodialysis, but a progressive increase of functional activity of PC was documented with hemodialysis. Furthermore, the coefficient of correlation between the antigen level and functional activity of PC improved significantly with dialysis treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

The Levels of Protein C and Protein S in Chronic Liver

The levels of protein C (PC) and protein S (PS) were assessed in plasmas derived from 39 patients with various chronic liver diseases and found to be significantly decreased. These decreased levels were positively correlated with the parameters for the protein synthesis in the liver, including cholinesterase, serum albmin, and hepaplastin test, suggesting that the synthesis of PC and PS were also decreased in these diseases. Interestingly, the patients with increased levels of T·AT and manifested decreased PC and PS levels in plasma. These inverse correlations seem to indicate that the decreased levels of PC and PS in plasma could precipitate the disseminated intravascular coagulation syndrome by virtue of insufficient regulation of accelerated blood coagulation.

Changes in the Plasma Levels of Coagulation Regulatory Factors in Patients with Nephrotic Syndrome

In 12 patients with nephrotic syndrome, the moleclar markers for hypercoagulability including thrombin-antithrombin III complex (TAT), plasmin-α2-plasmin inhibitor complex (PIC) and β-thromboglobulin (β-TG), and the coagulation regulatory factors including antithrombin III (AT III), heparin cofactor II (HC II), protein C (PC) and protein S (PS) were studied.Plasma levels of TAT, PIC and β-TG were all significantly high as compared to normal controls, and also they were inversely correlated with serum albumin levels and positively correlated with total urine protein levels.In the antithrombin-regulatory system, AT III was found decreased and significantly correlated with serum albumin and total urine protein levels, while HC II was rather increased when compard with normal controls. In the PC-regulatory system, PC was significantly increased, while PS activity was significantly reduced as compared to normal controls, and they were significantly correlated with total urine protein levels. Decreased PS activity was caused mainly by significant reduction in free (active) PS levels due to the selective and massive urinary loss of free PS and the elevation of C4b-binding protein (C4bp) levels which favor complex formation (C4bp-PS) with free PS.These results imply that the thrombotic tendency in nephrotic syndrome might be raised in parallel with the progression of disease activity, and high levels of PC and HC II would help to counteract hypercoagulability.

THE PROTEINS C-S SYSTEM IN CHILDREN WITH SECONDARY PULMONARY HYPERTENSION

Plasma levels of protein C (PC), total protein S (PSt) and free protein S (PSf) were assessed by electro-immunodiffusion in 6 healthy children (1 to 14 yr) and in 6 children with pulmonary hypertension and polycythemia secondary to congenital heart disease (3 to 15 yr) before and after intentional hemodilution (HD) which was planned to achieve a 10% decrease in hematocrit. Results are expressed as a percentage of antigen (mean ± SD). Severe pulmonary vascular damage and hyperviscosity are likely to be the main causes of consuption coagulopathy in this syndrome, with decreased plasma levels of PC and PSf which are not significantly improved by moderate hemodilution.

Hereditary protein C deficiency

Protein C (PC) is the central component of a major antithrombotic regulatory system with both anticoagulant and profibrinolytic properties. A deficiency of PC is one of several hereditary abnormalities of haemostatic proteins that have been described in patients with a propensity for thromboembolic complications. Major morbidity is often seen in these patients. The various aspects of hereditary PC deficiency in terms of clinical presentation, genetics, diagnosis and treatment of both homozygous and heterozygous states will be presented. In heterozygous deficiency, the levels of plasma PC are usually between 35% and 65% of normal, whereas the majority of normal individuals have levels between 70% and 130%. PC-deficient patients usually develop venous thrombotic complications between the ages of 15 and 40 years with a high incidence of DVT and pulmonary embolism. The majority of thrombotic lesions appear to develop spontaneously; others are associated with trauma, surgery or pregnancy. Treatment of symptomatic patients is initial heparin therapy followed by coumadin. After multiple thrombotic events, lifelong oral anticoagulant therapy is necessary. The potential complications of treatment are coumadin-induced skin necrosis, heparin-induced thrombocytopenia and bleeding. Homozygous PC deficiency, a rare but fatal hereditary condition, manifests itself with massive DIC and purpura fulminans in the newborn period. Effective treatment for these infants can be instituted with either oral anticoagulant therapy or PC replacement. The heterozygous deficiency of PC is similar to that found in other inherited disorders in that several genetic mechanisms are responsible for the expression of the disease. Both quantitative and qualitative decreases in PC exist, the former being type I deficiency and the latter, type II. The best initial diagnosis of either form involves a clotting (functional) assay while differentiation between the two also requires an antigenic (immunological) assay. Autosomal inheritance with significant variable penetrance is found with profound clinical implications. In summary, PC deficiency is one of a group of inherited disorders termed hereditary thrombotic disease, which may have serious implications for patient morbidity and mortality.

Protein C and protein S levels in two patients with acquired purpura fulminans

Purpura fulminans (PF) is a cutaneous manifestation of a dramatic and deadly syndrome of systemic disseminated intravascular coagulation (DIC). It is characterized by microvascular thrombosis in the dermis followed by perivascular haemorrhage. Since two other related syndromes involve the protein C (PC) system, we undertook a serial study to investigate the levels of PC and protein S (PS) in two patients with acquired PF. Laboratory findings were consistent with DIC, and both patients were treated with blood replacement and heparin therapy. The levels of PC activity were very low during the initial 24-36 h after onset and gradually increased until returning to normal levels. The total and 'free' PS were also abnormal during the initial onset of PF. The total and free PS increased to normal after 4-6 d. Although the pathogenesis is not fully understood, the infection and sepsis appears to consume PC and PS selectively during the PF and DIC phase. Acquired PF appears to selectively involve the PC system in a similar fashion to two other syndromes of PF-like lesions.

Homozygous Protein C Deficiency in Two Siblings

Homozygous protein C (PC) deficiency is reported in two siblings (girl and boy) who received their proper diagnoses at the ages of 7 4/12 and 1 3/12 years respectively. The girl had perinatal asphyxia without bleeding. At 1 year of age she developed purpura fulminans. Treatment with heparin and plasma was successful. At 7 4/12 years she developed tender, bluish nonnecrotic skin changes after an orthopedic operation. The PC level was 0.08 U/ml. The boy had had a large intraventricular hemorrhage neonatally and developed severe brain damage. At 1 3/12 years he manifested the same skin changes as his sister and was treated similarly. The PC level was 0.05 U/ml. Both children now receive warfarin continuously and are essentially free of symptoms. The cases represent homozygous phenotypes in a family with a recessive trait of PC deficiency without thrombotic disease. The cases also show that severe PC deficiency may be compatible with life beyond infancy without any specific therapy.

Effect of Protein C and Activated Protein C on Coagulation and Fibrinolysis in Normal Human Subjects

Although protein C (PC) and activated protein C (APC) have been postulated to be useful for treating patients with thrombosis, their critical effect remains to be studied in human subjects. To examine whether purified PC or APC are useful for treating patients with thrombosis without showing any adverse effect, we studied effects on coagulation and fibrinolysis in normal human subjects. When highly purified human PC was administered intravenously to healthy subjects, plasma levels of immunoreactive PC decreased with a half-life of 10.9 h. Intravenously administered APC decreased with a half-life of 23 min as measured by prolongation of activated partial thromboplastin time (APTT). However, 1.7 h was obtained for the plasma half-life of APC when it was measured immunologically. These findings suggested that a significant fraction of the administered APC was rapidly inhibited by plasma inhibitor. Upon administration of APC, APTT was prolonged and plasma levels of clotting factor VIII (F-VIII) decreased transiently as measured by clotting assay. However, when determined by a chromogenic assay method in which 120-fold diluted plasma samples were used, plasma levels of F-VIII remained unchanged. Plasma levels of F-V did not decrease after APC administration. These findings suggested that prolongation of APTT and apparent decrease in plasma F-VIII clotting activity might be due to the in vitro-effect of APC present in plasma samples used. Diurnal fluctuation of plasminogen activator inhibitor in normal subject was not affected by administration of APC. Thus, PC or APC seems to function selectively at the site of thrombin-formation without lowering plasma levels of coagulation factors.

The serial hemostasis-related changes in patients with cerebral infarction: comparison between progressing and non-progressing stroke

Serial determinations of beta-thromboglobulin (BTG), platelet factor 4 (PF4), fibrinopeptide A (FPA), anti-thrombin III (ATIII), protein C (PC), fibrin(ogen) degradation product (FDP), FDP D-dimer, activated partial thromboplastin time (APTT), prothrombin time (PT), and euglobulin lysis time (ELT) were performed in 18 patients with non-progressing stroke and 14 patients with progressing stroke in order to predict the development of progressing stroke. Increasing levels of BTG, PF4 and FDP with frequent fluctuation were noted in both kinds of stroke. Fluctuation of FPA levels was also noted but was less pronounced. PC levels were found to be slightly decreased with fluctuation but the mean was still in the lower normal limit. BTG, PF4 and PC all elevated at the time of deterioration of physical condition in patients with progressing stroke, whereas FPA had no definite change at that time. From out study, we conclude that both platelet activation and coagulation process do occur in both kinds of stroke. But the latter plays a minor role in the formation of thrombosis. The hemostasis change, especially concerning the thrombosis formation, probably plays a role in the development of progressing stroke, but we cannot predict their development even by the detections of the newly known molecular substances appearing in various steps of the hemostatic mechanism. Developtment of new tests for understanding the whole dynamic change of the thrombosis process is necessary for accurate prediction of the progressing stroke in the future.

Neonatal protein C: Molecular composition and distribution in normal term infants

Protein C (PC) is a vitamin K-dependent serine protease which functions as the central regulatory protein with both anticoagulant and profibrinolytic properties. The PC levels in healthy term newborns are approximately one third of adult levels. Severely decreased levels of PC are seen in sick term and preterm infants. These neonates appear to have an increased incidence of thrombosis. Undetectable levels of PC are found in homozygous PC deficient infants with DIC and purpura fulminans symptoms. In this present study we report the composition and distribution of PC in term newborn and compare the results with adult values. Plasma was obtained from placental cord blood of 20 healthy term (38–42 weeks gestation) infants. PC was immunopurified, run on SDS-PAGE, and immuno-blotted. The composition of the PC molecule in neonatal plasma is identical to that seen in adults. Using densitometry to determine the distribution of the PC components, we observed a 2-fold increase in single chain PC in the neonate as compared to the adult. In the neonate, there was an inverse correlation between the level of total PC antigen and the amount of single chain. These findings suggest the possibility that the processing of PC may be developmentally influenced.

The quantitative association of plasma endotoxin, antithrombin, protein C, extrinsic pathway inhibitor and fibrinopeptide a in systemic meningococcal disease

We have evaluated the quantitative relationship between lipopolysaccharide (LPS, endotoxin), fibrinopeptide A (FPA), antithrombin (AT), protein C (PC) and extrinsic pathway inhibitor (EPI) in plasma from 39 consecutively admitted patients with systemic meningococcal disease (SMD). The most severely ill patients with fulminant meningococcal septicemia (n=13, 6 dead) had significantly (p<0.01) higher plasma levels of LPS and FPA and lower levels of PC and AT on admission as compared with the less severe clinical presentations (n=26, 1 dead). The levels of EPI on admission were significantly (p<0.05) higher in nonsurvivors vs survivors with fulminant septicemia. As the disease progressed, the levels of LPS, FPA, AT and PC declined, while the levels of EPI increased. Three of six nonsurviving septicemic patients had levels of EPI >200% within 16 hours of admission vs two of 30 survivors (p=0.02). The results suggest that increasing levels of LPS in SMD elicit increasing consumption coagulopathy, contributing to the organ pathophysiology. The kinetics of EPI, inhibiting the thromboplastin-FVIIa-FXa complex, differs markedly from the kinetics of AT and PC i.e. increases as opposed to decreases.

Ｇｌａドメインを認識するモノクローナル抗体を用いた酵素免疫測定法による血しょうプロテインＣの定量 先天性プロテインＣ欠乏症およびワーファリン服用症例における検討

In four patients with hereditary protein C (PC) deficiency and 30 under stabilized warfarin therapy, plasma levels of PC were measured by an enzyme-linked immunosorbent assay (ELISA) using a monoclonal anti-PC antibody which recognizes a Gla-domain-related conformational change. The results were compared with those obtained by other methods (polyclonal ELISA, amidolytic and anticoagulant assays). Gla-PC levels measured by the monoclonal ELISA were very close to PC values obtained by other assays in patients with hereditary PC deficiency. In patients under stable warfarin therapy, each assay gave different PC values. The mean plasma level of total PC antigen measured by the polyclonal ELISA was 58.5±11.0%, Gla-PC antigen 35.3±13.0%, amidolytic activity 60.6±12, 4%, and anticoagulant activity 14.8±7.4%. Among these, anticoagulant activity and Gla-PC antigen correlated well with thrombotest values, prothrombin activity and factor X activity. These results indicate that the present monoclonal ELISA (Gla-PC) measures PC specifically, and that Gla-PC assay as well as anticoagulant assay can evaluate the physiological PC function in patients during oral anticoagulant therapy.

Functional Assays for Protein C Activity and Protein C Inhibitor Activity in Plasma

An assay system for protein C (PC) activity and PC-inhibitor in plasma was developed. The assay was based on: (1) binding of PC to wells of a microtiter plate coated with a murine monoclonal anti-PC antibody (C3) that did not interfere with the activity or activation of PC; (2) activation of immobilized PC with Protac C; (3) incubation with or without a source of activated PC inhibitor; and (4) measurement of amidolytic activity using the substrate S-2366. The activity assay was specific for PC and sensitive to less than 1 microliter of plasma or 4 ng PC. Inhibition of activated PC by plasma followed pseudo first order kinetics. Heparin caused a dose dependent increase in the inhibition rate with half maximal stimulation at approximately 3 U/ml and maximal stimulation at heparin concentrations greater than or equal to 10 U/ml. This assay is suitable not only for determination of functional plasma levels of PC and PC inhibitor activities but also for kinetic studies of inhibition of activated PC in complex systems, such as plasma. Studies showed that urokinase interfered with the inhibition of APC by plasma inhibitor(s).

Development of the human coagulation system in the healthy premature infant

This study was designed to determine the postnatal development of the human coagulation system in the healthy premature infant. Consecutive mothers of healthy premature infants born at either St Joseph's Hospital or McMaster University Medical Centre in Hamilton were asked for consent. One hundred thirty-seven premature infants (30 to 36 weeks of gestational age) entered the study. The premature infants did not have any major health problems and did not require ventilation or supplemental oxygen. Demographic information and a 20-mL blood sample were obtained in the postnatal period on days 1, 5, 30, 90, and 180. Between 40 and 96 premature infants were studied on each day for each of the following tests: prothrombin time, activated partial thromboplastin time, thrombin clotting time, plasminogen; 13 factor assays [fibrinogen, II, V, VII, VIII, IX, X, XI, XII, XIII, high-mol-wt kininogen (HMWK), prekallikrein (PK), von Willebrand factor (vWF)] and eight inhibitors [antithrombin III (AT-III), heparin cofactor II, alpha 2-antiplasmin, alpha 2-macroglobulin, alpha 1-antitrypsin, C1 esterase inhibitor, protein C (PC), and protein S (PS)]. A combination of biologic and immunologic assays were used. Between 30 to 36 weeks there was a minimal effect of gestational age for levels of AT-III, PC, and factors II and X only; therefore, the entire data set was used to generate reference ranges for these components of the coagulation system for premature infants. Next, the results for the premature infants were compared with those of a previously published study in 118 fullterm infants and with those for adults. An effect of gestational age was shown for plasminogen, fibrinogen, factors II, V, VIII, IX, XI, XII, HMWK, and all eight inhibitors. In general, the postnatal maturation towards adult levels was accelerated in premature infants as compared with the fullterm infants. By 6 months of age, most components of the coagulation system in premature infants had achieved near adult values.