Differentiation of fibrinolysis and fibrinogenolysis by analysis of FDP fragments]

We previously analysed the fragments of fibrin/fibrinogen degradation products (FDP) by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) combined with immunoblotting. In this report, we studied the semi-quantitative analysis of fibrinolysis (degradation of cross-linked fibrin) and fibrinogenolysis (degradation of fibrinogen and/or unstable fibrin) of patients' samples by our method. In vitro study of FDP made it clear that an appearance of D fragment confirmed fibrinogenolysis and an appearance of DD fragment and/or high molecular weight fragments which have higher molecular weight than DY or X fragment confirmed fibrinolysis. In addition, a study with mixtures of various concentrations of fibrin degradation products (FbDP) and fibrinogen degradation products (FgDP) demonstrated a dose dependent intensity of band by immunoblot method. These results show that our method is favorable for the semi-quantitative analysis of fibrinolysis and fibrinogenolysis. We applied the method to 6 samples from patients with disseminated intravascular coagulation (DIC). Consequently, fibrinogenolysis was observed in all of 6 samples, in which fibrinogenolysis was more enhanced than fibrinolysis in one sample, and an equivalent degree of fibrinolysis and fibrinogenolysis were observed in 3 of 6 samples. Although our method was probably devoid of the ability to distinguish FgDP from degradation products of unstable fibrin, these findings indicate that fibrinogenolysis is, at any rate, enhanced in the majority of patients with DIC, besides fibrinolysis.     

Clinical application of laboratory diagnosis: leukemia and DIC]

Plasma levels of molecular markers of hemostatic activation were investigated in 205 samples from patients with haematopoietic malignancies. These markers included thrombin/antithrombin III complex (TAT), D-dimer, plasmin/alpha 2plasmin inhibitor complex (PIC) and thrombomodulin (TM), and were assayed by EIA methods. Samples were divided into 4 groups according to the level of FDP: group A; FDP 10 greater than, group B; 10 less than or equal to less than 20 group C; 20 less than or equal to less than 40, and group D; less than 40. The mean level of each marker except TM increased in the order of group A, B, C and D. However, in many samples belonging to group A the plasma TAT or PIC levels and both were increased in spite of low FDP level. Furthermore, levels of TAT and PIC in several samples belonging to groups C and D were within the normal range. Also, the mean levels of each marker except TM increased in the order of 2, 3, 4, 5 and over 6 points in DIC score according to the criteria of DIC diagnosis by the research committee on DIC of the Ministry of Health and Welfare in Japan. Eight of the 11 samples (72.7%) obtained from cases with a DIC score of 3 points had high plasma levels of TAT, PIC and D-dimer. Plasma levels of these markers were increased after chemotherapy. These findings lead to the following conclusions: 1) FDP reflexed activation of coagulation and fibrinolysis, but 2) FDP was not more sensitive than TAT and PIC, and 3) the increase of FDP rarely resulted from fibrinogenolysis or non-plasmin mediated fibrinolysis. Furthermore, 4) TAT, D-dimer and PIC may serve as sensitive parameters of hemostatic activation in circulating blood and be valuable markers for early diagnosis of DIC.     

Clinical usefulness of the measurement of plasma D-dimer levels

To evaluate the clinical usefulness of D-dimer, various effects on the measurement of D-dimer were examined. Although both fibrinolytic and fibrinogenolytic products were detected by the measurement of FDP, only fibrinolytic products were detected by the measurement of D-dimer. In patients with DIC and other thrombo-embolic diseases, plasma D-dimer levels were significantly higher than in normal persons. A significant positive correlation between plasma D-dimer and serum FDP was found in DIC patients. In patients with DIC associated with acute promyelocytic leukemia, which is thought to be an increased fibrinogenolysis state, serum FDP was higher than the plasma D-dimer which suggests that increased fibrinogenolysis affects the result of serum FDP measurement. Plasma D-dimer significantly increased 5 minutes after endoscopic embolization with thrombin in the patients with esophageal varices. However serum FDP increased 30 minutes after the treatment, which suggests that the D-dimer is more useful for rapid detection of coagulo-fibrinolytic change than serum FDP. Plasma D-dimer was significantly higher in patients with cerebral infarction and increased with age. These finding suggest the usefulness of plasma D-dimer measurement for the specific and rapid evaluation of coagulo-fibrinolytic activation and thrombo-embolic state.     

Serum FDP assay with latex photometric immunoassay and its analysis by immunoblotting

Sixty patients' sera with FDP-E value ranged from 200 to 2,500 ng/ml by LPIA system were assayed for FDP-Total (FDP-T) by the same system and FDP-DD by ELISA. Correlations of values between FDP-E, FDP-T and FDP-DD were excellent and ratio of FDP-T/FDP-E (T/E) and FDP-DD/FDP-E (DD/E) from same 60 sera were 32.4 + 7.4 and 1.55 + 0.50, respectively. Ratio of T/E from sera of FDP-E value demonstrating more than 500 ng/ml were classified into three groups, namely, 25.0-35.0, less than 18.0, and more than 50.0. Ten sera in each group were analyzed for FDP fragments of D, DD, Y, DY or X (DY/X) and high molecular weight (HMW) with SDS-PAGE and immunoblot method. It was found that relative concentration and proportion of D and DD.E fragments showed its characteristic pattern in each group.     

Analysis of cross-linked fibrin and fibrinogen degradation products with SDS-PAGE and immunoblot

SDS-PAGE and immunoblot technique with anti-FDP-D, -FDP-E, -fibrinogen antibody or anti-FDP-DD monoclonal antibody were applied to analyze FDP fragments prepared from cross-linked fibrin and fibrinogen with plasmic digestion in vitro. FDP fragments of DY(260K), DD(187K), X(245K), Y(166K), D(77K, 97K), E1(58K), E2(46K) and E3(40K) were identified from data of molecular weight and reactivity to four antibodies referred to reports of other investigators. Serum FDP fragments from five DIC suspected patients were analyzed by the same methods. In two patients' sera, DD fragment was a main component, and in the other three patients' sera, D fragment was a main fraction. Proportions of high molecular weight fragments of FDP were considerably different in patients' sera. Appearance of D fragment in our cases was considered to be derived from unstable fibrin (fibrin monomer and dimer) rather than from fibrinogen. Molecular weight of DD fragments from patients' sera had heterogeneity (160 approximately 180K), and the values were different from that (187K) prepared from cross-linked fibrin. In conclusion, SDS-PAGE and immunoblot analysis of serum fragments of FDP will be an useful technique to investigate the clinical and pathological condition of DIC.     

Clinical significance of a new fibrinogen/fibrin degradation products(FDP) test using plasma samples for the diagnosis of fibrinogenolysis and fibrinolysis

Recently, a new fibrinogen/fibrin degradation products(FDP) test using monoclonal antibodies against FDP(LPIA FDP-P: FDP-P) has been developed, which is able to measure FDP directly in plasma. The objective of this study is to clarify clinical significance of the test in the diagnosis of fibrinogenolysis and fibrinolysis in comparison with a conventional FDP test using polyclonal antibodies against fibrinogen(FDP-S) and D-dimer test using monoclonal antibodies against D-dimer(D-D). The monoclonal antibodies used in FDP-P test was shown to recognize fragment X, Y and D1 derived from fibrinogen digested by urokinase, and was also to recognize XDP fragments, D-dimer and D derived from cross-linked fibrin digested by tissue plasminogen activator using SDS-PAGE and immunoblotting analysis. There was a good correlation of FDP levels between FDP-P test and FDP-S test. However, levels of FDP in both tests were discrepant in several samples. There was a tendency that the levels of FDP were higher in FDP-S test than in FDP-P test. Such discrepancy was suggesting that soluble fibrin monomer complex(FM) was recognized by the antibodies used in FDP-S test, but not recognized by the antibodies used in FDP-P test. There was also a good correlation of FDP levels between FDP-P test and D-D test. However, the levels of FDP in both tests were discrepant in several samples. The levels of FDP were higher in FDP-P test than in D-D test. These discrepant samples had lower levels of antiplasmin and higher levels of plasmin antiplasmin complex(PIC), and also showed XDP fragments, D-dimer, X, Y, and D1 by using SDS-PAGE. These observations suggest that D-D test measures only fibrinolytic fragments, while FDP-P test measures fibrinogenolytic fragments as well as fibrinolysis. In results, the FDP-P test was confirmed to be a useful tool to examine fibrinogenolysis as well as fibrinolysis more specifically than the conventional FDP test.     

Incidence and possible reasons for discordant results between positive FDP and negative D-dimer latex assays in clinical specimens.

In general, FDP and D-dimer values have a correlation in clinical conditions associated with disseminated intravascular coagulation(DIC) or coagulation activation. However, there are some patients with discordant results who demonstrate elevated FDP and negative D-dimer results by latex agglutination assays. The incidence and possible reasons for the discordance between FDP and D-dimer results were investigated through simultaneous measurements (n = 763) from clinical patients with suspected DIC or coagulation activation. 24.8% (189/763) of samples with elevated FDP were negative for D-dimer assays by the latex agglutination method. Further detailed analysis on randomly-selected discordant samples (n = 41) revealed that the most common reason for the discordance was the lower sensitivity of the semiquantitative latex agglutination method for D-dimer, compared with quantitative enzyme or other latex immunoassay. The other contributing factors to the discordance were accelerated fibrinogenolysis without secondary fibrinolysis, elevated soluble fibrin monomer and rheumatoid factor.     

A case of hookworm infestation with dissociation values between FDP-E and FDP-D dimer

We previously reported a five-year-old girl showing bleeding tendency and transient morphological and functional platelet abnormalities probably due to a hookworm, Necator Americanus, infestation. In this report, we describe the rarely accelerated fibrinogenolysis and/or fibrinolysis in this patient whose value of fibrinogen and/or fibrin degradation products(FDP) determined with an FDP-E assay was much higher than that determined with a D-dimer assay. Namely, on day-1 and day-13 of hospitalization, her D-dimer values were only 10 to 20% of the prospected values from FDP-E values. We speculated this phenomenon was induced by circulating protease(-like) agent(s) produced by hookworm, because the only slightly participation of plasmin and/or granulocyte elastase was evaluated by the determination of enzyme-inhibitor complexes. And the other possibility of fibrinogen degradation by blast- or tumor-associated protease was excluded by the clinical manifestations and primary disorders. In conclusion, we report a very rare case with the accelerated fibrinogenolysis and/or fibrinolysis in a patient with the hookworm infestation. We are interested in the mechanism that manifested the patient's bleeding tendency accompanied with morphological and functional platelet abnormalities.     

Differentiation between fibrin degradation products and fibrinogen degradation products by using newly developed ELISAs

We should distinguish fibrin degradation products (FbDP) from fibrinogen degradation products (FgDP) in order to analyze fibrinolysis in vivo. We analyzed some disorders associated with hyperfibrinolytic states using ELISA for FbDP, FgDP and total fibrin (ogen) degradation products (TDP) (ORGANON TEKNIKA). Each ELISA was useful in terms of reproducibility and dilution linearity of plasma samples. There was no cross-reaction between FbDP and FgDP. The FgDP/FbDP ratio in normal individuals was 1.65. In patients with DIC, it was 0.43, with FgDP level being increased. These results suggest that fibrinolysis is enhanced in patients with DIC, but it is accompanied by fibrinogenolysis. On the other hand, the FgDP/FbDP ratio in patients given urokinase (UK) was 2.88. This suggests that fibrinogenolysis is enhanced in them. In our study, the FgDP/FbDP ratio increased as DIC improved. Thus, we can regard this as an index of therapeutic effects in patients with DIC. We conclude that these three ELISA are useful in analyzing disorders associated with hyperfibrinolytic states.     

Interpretation of hemostatic and fibrinolytic markers

Blood dose not normally coagulate in the blood vessels covered with endothelial cells, because these cells contain some substances responsible for antithrombotic action such as thrombomodulin, heparin-like substance, prostacyclin, nitric oxide and tissue plasminogen activator. Most important role of blood coagulation is hemostasis. Blood can coagulate in two ways: intrinsic coagulation pathway and extrinsic coagulation pathway that is activated by negatively charged substances and FVIIa-tissue-factor (TF) complex, respectively. Prothrombin time(PT) can represent extrinsic pathway, while activated partial thromboplastin time (APTT) can represent intrinsic pathway. PT is prolonged in such diseases as vitamin K deficiency, hepatic failure and warfarin intake, while APTT is prolonged such diseases as hemophilia A & B, von Willebrand disease and lupus anticoagulant. Cross mixing test is very useful to assess prolonged clotting time. FDP means fibrin/fibrinogen degradation products and D-dimer is the smallest products of fibrin degradation. These markers are often used to diagnose disseminated intravascular coagulation (DIC) and deep vein thrombosis (DVT). Thrombin-antithrombin complex (TAT) and plasmin-alpha2 plasmin inhibitor (PIC) can be used to evaluate the extent of coagulation and fibrinolysis activation, respectively. These two markers is essential for classify the pathophysiology of DIC: DIC with suppressed fibrinolysis, enhanced fibrinolysis or balanced fibrinolysis. In conclusion, exact interpretation of hemostatic and fibrinolytic markers is one of the most important abilities in clinical situation.     

Analysis of antibody reactivity for FDP D-dimer fragments by Western blotting

We evaluated three test kits for fibrin degradation products (FDP) D-dimer. We found that six of 217 plasma sample values obtained by Nanopia test were markedly higher than the values obtained using the other two kits. The regression equation for 211 samples (excluding six) was y=0.64x+3.05 (y: Nanopia, x: LIAS AUTO) and the correlation coefficient was 0.915. Therefore, we classified these samples into three categories, namely correlated(y< 1.0x), incompatible (y= 1.0x-2.9x) and markedly incompatible (y> or =3.0x). Selected samples, eight correlated, four incompatible and four markedly incompatible, were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis followed by Western blotting(WB). WB analysis using anti-fibrinogen antibody showed that both high molecular weight fragments of cross-linked fibrin (HMW-XDP) and DD/E fragments were present in the correlated samples, but there was less HMW-XDP than DD/E in the incompatible samples and mostly DD/E (HMW-XDP was significantly less than DD/E) in the markedly incompatible samples. These data suggest that plasma FDP samples that contain mostly DD/E and little HMW-XDP demonstrated markedly incompatible values using the three D-dimer test kits. These data was reflected by markedly elevated plasmin alpha2-plasmin inhibitor complex values in the incompatible and markedly incompatible samples. Unfortunately, we did not directly demonstrate these phenomena by WB analysis with two anti-D-dimer antibodies used Nanopia or LPIA reagent. In the near future, we expect that standardization of FDP D-dimer assay will be accomplished.     

Coagulation and fibrinolysis parameters in disseminated intravascular coagulation (DIC)]

Eighty six plasma samples from 41 patients with suspected disseminated intravascular coagulation (DIC) were divided into 3 groups as follows: Group A, 53 samples from established DIC; Group B, 19 samples from possible DIC; and Group C, 14 samples from probable DIC. The following parameters of coagulation and fibrinolysis were evaluated: thrombin/antithrombin III complex (TAT), plasmin/alpha 2 plasmin inhibitor complex (PIC), D-dimer (D-D) and fibrin monomer (FM). In Group A, TAT and PIC were significantly elevated, being 29.5 +/- 20.7 micrograms/l and 7.2 +/- 6.1 mg/l respectively, suggesting marked hypercoagulability and accelerated fibrinolysis. There were no correlations between antithrombin III (ATIII) and TAT, between alpha 2 plasmin inhibitor (alpha 2PI) and PIC, or between TAT and PIC, showing the clinical diversity of patients with DIC. In all groups abnormal TAT, PIC and D-D findings were observed in many samples (86-100%), and FM was present in 83%, 63%, and 29% of samples in Groups A, B, and C respectively. In Groups B and C, abnormal findings for TAT, PIC, D-D, FM and alpha 2PI apparently indicated hypercoagulability and accelerated fibrinolysis, even though fibrinogen and platelet count were within normal limits.     

Measurement of plasma fibrin D-dimer levels with the use of a monoclonal antibody coupled to latex beads

Recently, monoclonal antibody (DD-3B6) to fibrin D-dimer was prepared and coupled to latex beads to provide a specific test (Dimertest) for fibrinolysis. The purpose of this study was to evaluate the Dimertest assay as a clinical laboratory test for the measurement of plasma fibrin D-dimer derivatives. The Dimer-test assay specifically detected 2 micrograms/mL of purified fibrin D-dimer or fibrin D-dimer/fragment E complex added to afibrinogenemic plasma but did not detect 500 micrograms/mL of either fibrinogen fragments X, D, E, or 160 micrograms/mL cross-linked fibrinogen. The fibrin(ogen) degradation product (FDP) assays of American Dade or Wellcome Diagnostics detected 5.0 micrograms/mL of fibrin D-dimer and from 1 to 10 micrograms/mL of the other FDPs. Twenty-eight percent of 150 random plasma samples assayed from hospitalized patients were positive for fibrin D-dimer derivatives. Plasma samples from 152 patients suspected of having disseminated intravascular coagulation (DIC) were assayed for serum FDP (Wellcome Diagnostics) and plasma fibrin D-dimer derivatives. Samples from 69% of patients with serum FDP levels less than 10 micrograms/mL, and more than 90% of those with serum FDP levels greater than 10 micrograms/mL, were positive for fibrin D-dimer derivatives. Dimertest results were not modified by heparin, streptokinase, freeze-thawing, or clotting plasma. Serum fibrinogen-related antigens were immunoadsorbed from Dimer-test positive sera by anti-fibrinogen antibody and formalin-fixed Cowan I strain Staphylococcus aureus. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and protein blotting with the use of monoclonal antibody DD-3B6 demonstrated a protein band with similar mobility to purified D-dimer. The measurement of plasma fibrin D-dimer derivatives by the Dimertest assay is a rapid, sensitive, and specific laboratory test for fibrinolysis. The Dimertest assay has proven to be a useful addition to the clinical laboratory and should be helpful in the diagnosis and management of patients with diseases associated with fibrinolysis.     

Correlations among FPB beta 15-42, PAC and D-dimer]

We measured FPB beta 15-42, and alpha 2 plasmin inhibitor-plasmin-complex (PAC), which are direct indexes of plasmin activity, as well as D-dimer in 204 samples from patients with subarachnoid hemorrhage, trauma, and the patients during cardiopulmonary bypass. In all patients, these molecular markers increased due to secondary fibrinolysis; these increases were significantly higher in DIC patients. There were positive correlations among the molecular markers. The correlation coefficient for FPB beta 15-42 and D-dimer was significantly higher than that for PAC and D-dimer in the DIC patients. In conclusion, it might be better to measure both FPB beta 15-42 and PAC as indexes of plasmin activity in DIC patients, because of the significant difference between the correlation coefficient for PAC and D-dimer, and that for FPB beta 15-42 and D-dimer.     

Prevention of fibrinogenolysis without impairment of thrombolysis: Combination of A Plasminogen Activator with a2-antiplasmin

The thrombolytic therapy is usually associated with bleeding risks due to a systemic fibrinogenolysis. We investigated whether it is possible to block fibrinogenolysis without impairing the lytic activity of fibrin-bound plasmin molecules. The present data show that at increased a2-antiplasmin levels as high as 6-fold the normal concentration fibrinolysis was not impaired, while the haemostatic parameters as aPTT, TT and the fibrinogen concentration remained normal. Essentially similar results were observed with all plasminogen activators (streptokinase, urokinase and a t-PA mutant) assayed. The use of a₂-macroglobulin leads to identical observations. With aprotinin, however, a complete inhibition of the lysis was observed. The data presented here show that it is possible with the combined use of a plasminogen activator and a2-antiplasmin to reach at least in vitro a normal fibrinolysis without impairment of the haemostatic parameters.     

Diagnosis of disseminated intravascular coagulation. Role of D-dimer

Detection of the cross-linked fibrin degradation fragment, D-dimer, in patients at risk for disseminated intravascular coagulation (DIC) is strong evidence for the diagnosis. D-dimer confirms that both thrombin generation and plasmin generation have occurred. Patients at risk for DIC (58) and normal controls (7) were studied. Thirty-three patients had DIC--with fragment D-dimer identified in their serum by immunoblotting. Latex agglutination measurements of fibrin(ogen) degradation products (FDPs) and D-dimer were compared with immunoblotting in the detection of D-dimer. FDP measurement was extremely sensitive but not specific. D-dimer measurement was less sensitive but highly specific. Used in tandem, screening with FDP and confirming with D-dimer, sensitivity and specificity were maximized, rendering a predictive value of a confirmed FDP of 100% in this cohort. D-dimer is a valuable adjunct for the laboratory diagnosis of DIC but is most appropriately used as a confirmatory test for the very sensitive FDP test.     

Degradation of adsorbed fibrinogen by surface-generated plasmin

An investigation of the physical status of fibrinogen that has been adsorbed to glass and then eluted has been conducted. Exposure of Kabi fibrinogen to glass was carried out using a glass bead column experiment. The fibrinogen was eluted sequentially, first by 1 M Tris and then by SDS. The initially eluted fibrinogen showed considerable degradation (SDS polyacrylamide gel electrophoresis) while the later fractions were less degraded. Fibrinogen purified by chromatography on either DEAE-cellulose or Sepharose-lysine to remove plasminogen was less degraded. When purified plasminogen was added to fibrinogen, degradation of column eluates was very extensive in all eluted fractions. These results are interpreted in terms of a surface-mediated activation of plasminogen to plasmin followed by fibrinogenolysis. Although such an effect remains to be demonstrated as a general property of surfaces, it is speculated that surfaces may vary in their activation of fibrinolysis as well as their activation of clotting, and that maximization of fibrinolysis is a worthwhile goal in the development of blood-compatible surfaces.     

Thrombin.antithrombin III complex

Increase of TAT is reflected by the generation of thrombin in hypercoagulable state. TAT might increase in DIC characterized by the formation of disseminated micro-thrombosis. DIC was classified into three groups according to the results of screening tests (FDP, platelet count, fibrinogen, prothrombin time). TAT values significantly increased in the stage of pre-DIC compared with the control group consisting of DIC prone underlying disease. Pre-DIC was easily detected by an increase of TAT during the clinical course. Management of high TAT began with the use of an anticoagulant such as heparin under the condition of sufficient ATIII level. The lowering effect of TAT was easily obtained by the anticoagulant. In ATIII-deficient DIC, the high TAT reduced with the substitution of ATIII concentrate, though a transient increase of TAT was found during the administration of ATIII. To reduce the high TAT under the deficient state of ATIII, MD805, a synthetic thrombin inhibitor, was introduced to avoid further consumption of ATIII. The TAT was decreased by the use of MD805 without administration of ATIII. MD805 could be used as an effective anticoagulant in high TAT due to DIC under an ATIII-deficient state. Although the TAT improved with an adequate anticoagulation in DIC, spontaneous bleeding sometimes appeared as a complication associated with the high level of alpha 2 plasmin inhibitor plasmin complex. In this case, the combined use of tranexamic acid relieved the bleeding.     

Clinical evaluation of a test for plasma fibrin/fibrinogen degradation products (FDP) based on monoclonal anti-FDP antibody technology: an application for the scoring system of the disseminated intravascular coagulation (DIC) diagnostic criteria

Fibrin/fibrinogen degradation products(FDP) have been measured using serum samples which were specially prepared for the FDP test because of the usage of anti-human fibrinogen antibody for the assay. Since diagnostic criteria for DIC were established by the study group on thrombosis and hemostasis which is supported by the Japanese Ministry of Health and Welfare(JMHW), serum FDP assay have been used as standard methods to diagnose DIC in Japan. Recently, a reagent using an anti-human FDP monoclonal antibody was developed and this has enabled the use of plasma samples for FDP measurement. The comparability, especially of the DIC score, of a new assay, Latex test BL-2 P-FDP, using plasma samples with a conventional assay for serum was investigated. Two sets of DIC scores based on data from the two tests were compared and the correlation was high with 97.5% of the patients being diagnosed with the same DIC status. In four disease groups--DIC, thrombosis, leukemia and solid cancer--high comparability between the two tests was also shown and no significant difference was observed in the correlation coefficient and the slope coefficient between serum and plasma samples. To conclude, it is suggested that "Latex test BL-2 P-FDP" is applicable to the diagnostic criteria for DIC from JMHW without any difficulty.     

Physiologic regulation and pathologic disorders of fibrinolysis

Physiologic fibrinolysis is a reparative process that occurs in response to hemostatic plug or thrombus formation. The final enzymatic step, fibrin proteolysis, results from a coordinated interaction of enzymes and inhibitors, which produces effective action at the site of the disease and spares the proteins of the blood or uninvolved parts of the vascular system. The agent of fibrinolysis, the enzyme plasmin, is derived from its zymogen (plasminogen) through limited proteolysis effected by plasminogen activators. They can be grouped according to functional and immunologic properties into the tissue type and urokinase-like plasminogen activators. The ability of alpha 2 antiplasmin to neutralize efficiently free (nonfibrin-bound) plasmin prevents inappropriate systemic activation of fibrinolysis. This control is superseded in certain conditions, such as with the therapeutic administration of plasminogen activators to lyse pathologic thrombi, when plasmin degrades plasma fibrinogen into degradation fragments (X, Y, D, and E). Degradation of cross-linked fibrin results in distinctive products that are characterized by cross-linked (factor XIIIa-induced) derivatives such as D dimer. Disease states resulting from abnormalities in the fibrinolytic system include both hemorrhagic disorders, resulting from excessive fibrinolysis, and thrombosis, as the result of deficient fibrinolysis. Hyperfibrinolysis can result from pharmacologic administration of activators or from defective inhibition produced by alpha 2 antiplasmin deficiency. Hypofibrinolytic thrombosis can result from hereditary defects, for instance of plasminogen or fibrinogen, or from pharmacologic inhibition of fibrinolysis such as with epsilon aminocaproic acid. Laboratory evaluation of fibrinolysis is useful for monitoring fibrinolytic therapy and assessing thrombotic disorders and bleeding; it also includes the specific measurements of plasminogen activator, plasminogen, plasmin, inhibitors and circulating fibrinogen, and cross-linked fibrin degradation products.