Under physiological conditions, the two systems of blood coagulation and anticoagulation in the body maintain a dynamic balance to keep the blood flowing in the blood vessels. If the balance is imbalanced, the anticoagulation system is predominant and the bleeding tendency is prone to occur, and the coagulation system is predominant and thrombosis is prone to occur. The fibrinolysis system plays an important role in thrombolysis. Today we will talk about the other two indicators of the fibrinolysis system, D-dimer and FDP, to fully understand the hemostasis generated by thrombin to the thrombus initiated by fibrinolysis. Evolution. Provide clinical basic information about patients' thrombosis and coagulation function.
D-dimer is a specific degradation product produced by fibrin monomer cross-linked by activated factor XIII and then hydrolyzed by plasmin. D-dimer is derived from cross-linked fibrin clot dissolved by plasmin. Elevated D-dimer indicates the presence of secondary hyperfibrinolysis (such as DIC). FDP is the general term for the degradation products produced after fibrin or fibrinogen is broken down under the action of plasmin produced during hyperfibrinolysis. FDP includes fibrinogen (Fg) and fibrin monomer (FM) products (FgDPs), as well as cross-linked fibrin degradation products (FbDPs), among which FbDPs include D-dimers and other fragments, and their levels increase High indicates that the body's fibrinolytic activity is hyperactive (primary fibrinolysis or secondary fibrinolysis)
【Example】
A middle-aged male was admitted to the hospital and the results of blood clotting screening were as follows:
| Item | Result | Reference Range |
| PT | 13.2 | 10-14s |
| APTT | 28.7 | 22-32s |
| TT | 15.4 | 14-21s |
| FIB | 3.2 | 1.8-3.5g/l |
| DD | 40.82 | 0-0.55mg/I FEU |
| FDP | 3.8 | 0-5mg/l |
| AT-III | 112 | 75-125% |
The four items of coagulation were all negative, D-dimer was positive, and FDP was negative, and the results were contradictory. Initially suspected to be a hook effect, the sample was re-examined by the original multiple and 1:10 dilution test, the result was as follows:
| Item | Original | 1:10 dilution | Reference Range |
| DD | 38.45 | 11.12 | 0-0.55mg/I FEU |
| FDP | 3.4 | Below the lower limit | 0-5mg/l |
It can be seen from the dilution that the FDP result should be normal, and the D-dimer is not linear after dilution, and interference is suspected. Exclude hemolysis, lipemia, and jaundice from the status of the sample. Due to the disproportionate results of the dilution, such cases may occur in common interference with heterophilic antibodies or rheumatoid factors. Check the patient's medical history and find a history of rheumatoid arthritis. Laboratory The result of the RF factor examination was relatively high. After communicating with the clinic, the patient was remarked and issued a report. In the later follow-up, the patient had no thrombus-related symptoms and was judged to be a false positive case of D-dimer.
【Summarize】
D-dimer is an important indicator of negative exclusion of thrombosis. It has high sensitivity, but the corresponding specificity will be weak. There is also a certain proportion of false positives. The combination of D-dimer and FDP can reduce a part of D- For the false positive of dimer, when the laboratory result shows that D-dimer ≥ FDP, the following judgments can be made on the test result:
1. If the values are low (<Cut-off value), there is no clinical significance. The report is issued directly, and the remarks indicate that it has no clinical significance.
2. If the result is a high value (>Cut-off value), analyze the influencing factors, there may be interference factors. It is recommended to do multiple dilution test. If the result is linear, a true positive is more likely. If it is not linear, false positives. You can also use the second reagent for verification and communicate with the clinic in time.
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