Clotting and D-dimers: the pathway in the body

This page shows the biochemical pathway behind the laboratory value D-dimers: which stations follow one another, which enzymes carry out each step and which cofactors they use. Every statement has a source. The page describes general textbook knowledge and says nothing about any individual person.

In brief

D-dimers are fragments of cross-linked fibrin, the protein mesh of a blood clot. They form when the enzyme plasmin dissolves a clot and so show that clotting and clot breakdown have occurred in the body.

The pathway step by step

Each station states what the compound does there. Three signs: ↑ supplies — builds up or makes available · ↓ depletes — inhibits, consumes or withholds · ↕ both, depending on amount. Behind it stands what the statement rests on: established physiology, observed in studies, or contested. The signs do not grade; they name the direction.

1. Prothrombin → Thrombin factor Xa · factor Va, calcium Factor Xa, together with its helper factor Va, cleaves prothrombin into thrombin. Thrombin is the central enzyme of clotting. Source 1↕ both, depending on amount Thrombin turns fibrinogen into fibrin and activates platelets and factor XIII. Bound to thrombomodulin, however, it switches on the braking protein C. established physiology Source 1, 4
   ⚖ When the balance tips

   too much — If much thrombin forms, a lot of fibrin is made quickly; antithrombin captures free thrombin.

   too little — If little thrombin forms, less fibrin is made and a plug stays loose.

   established physiology · Source 1

2. Fibrinogen → Fibrin thrombin Without the cleaved-off pieces, the molecules join end to end and side by side. This forms strands that hold blood cells in place. Source 2↑ supplies Fibrin strands supply the framework that firms up the platelet plug at the injury. established physiology Source 2
   ⚖ When the balance tips

   too much — If much fibrin forms, the mesh becomes dense and firm.

   too little — If little fibrin forms, the plug stays soft and dissolves more easily.

   established physiology · Source 2

3. Fibrin → Fibrin mesh factor XIIIa · calcium Factor XIIIa firmly links neighbouring fibrin strands, above all between their D domains. This makes the mesh stable and harder to dissolve. Source 3↑ supplies Cross-linking supplies strength: the mesh withstands pressure and is broken down more slowly by plasmin. established physiology Source 3
   ⚖ When the balance tips

   too much — If cross-linking is extensive, the mesh resists breakdown for longer.

   too little — If factor XIII is not very active, the mesh stays loose and is broken down faster.

   established physiology · Source 3

4. Plasminogen → Plasmin t-PA, u-PA The activators t-PA and u-PA convert plasminogen into plasmin. Plasmin cuts the fibrin mesh into soluble fragments. Source 4↓ depletes Plasmin breaks down the clot once the vessel is sealed. It is held in check by α2-antiplasmin, and its activators by PAI-1. established physiology Source 4
   ⚖ When the balance tips

   too much — If much plasmin forms, fibrin is broken down quickly and a clot lasts for a shorter time.

   too little — If little plasmin forms, fibrin stays in place longer.

   established physiology · Source 4

5. Fibrin mesh → D-dimers plasmin When plasmin cuts cross-linked fibrin, pieces remain in which two D domains are joined by factor XIIIa. They arise only from fibrin that was formed and cross-linked beforehand. Source 5, 3↓ depletes D-dimers have no known task of their own. They are remnants of the dissolved mesh and show that clotting and clot breakdown have both occurred. established physiology Source 5
   ⚖ When the balance tips

   too much — If much fibrin is formed and dissolved again, for example after surgery, during pregnancy or with inflammation, D-dimers rise.

   too little — If little fibrin is formed or dissolved, few D-dimers arise; anticoagulant medicines reduce their formation.

   established physiology · Source 5

6. D-dimers → Clearance D-dimers are removed from the blood within hours via the kidneys and by phagocytes. Their amount therefore mainly shows what has happened recently. Source 5↓ depletes Clearance continuously removes D-dimers from the blood; without new formation their amount falls quickly. established physiology Source 5
   ⚖ When the balance tips

   too much — If D-dimers are removed quickly, the amount soon falls again after an event.

   too little — If the kidneys filter more slowly, D-dimers stay in the blood longer.

   established physiology · Source 5

Further stations

• Prothrombin — made with vitamin K Prothrombin is made in the liver. In the process, vitamin K converts glutamate residues that bind calcium; only then can it be activated on membranes. Source 6, 1↑ supplies Prothrombin is the store from which thrombin is formed when needed. It is converted on the surface of activated platelets, that is, where an injury lies. established physiology Source 1, 6
  ⚖ When the balance tips

  too much — If plenty of prothrombin is present, a lot of thrombin can form quickly at an injury.

  too little — If prothrombin is made without vitamin K, it lacks the calcium-binding sites and is hardly activated on membranes.

  established physiology · Source 6, 1

• Fibrinogen — dissolved in plasma Fibrinogen is a large protein from the liver, dissolved in the blood. Thrombin cleaves small pieces off it. Source 2↑ supplies Fibrinogen supplies the building material of the clot. After cleavage, the molecules assemble into strands by themselves. established physiology Source 2
  ⚖ When the balance tips

  too much — If there is much fibrinogen in the blood, denser fibrin meshes form.

  too little — If little fibrinogen is present, thinner, looser meshes form.

  established physiology · Source 2

• Plasminogen — from the liver Plasminogen is the precursor of the enzyme plasmin. Together with its activator t-PA, it attaches to lysine residues of fibrin. Source 4↑ supplies Plasminogen supplies the store for clot breakdown. Because it is activated on the fibrin itself, plasmin acts mainly where a clot lies. established physiology Source 4
  ⚖ When the balance tips

  too much — If much plasminogen is bound to fibrin, more plasmin forms there.

  too little — If little plasminogen is present, a clot dissolves more slowly.

  established physiology · Source 4

Cofactors in this pathway

• Vitamin K — Needed in the liver to turn glutamate residues of prothrombin and other factors into calcium-binding Gla residues Source 6
• Calcium — Binds to the Gla residues and anchors the factors to membranes; also used by factor XIIIa Source 6, 3
• Glutamate — Amino acid residues in prothrombin that vitamin K converts into calcium-binding Gla residues Source 6In the ORY catalogue as a laboratory value: Glutamat
• Glutamine — Factor XIIIa links glutamine residues of one fibrin strand to lysine residues of the next Source 3In the ORY catalogue as a laboratory value: Glutamin
• Lysine — Lysine residues on fibrin are docking sites for plasminogen and t-PA and partners in cross-linking by factor XIIIa Source 4, 3In the ORY catalogue as a laboratory value: Lysin

What acts on this pathway

• Factor Xa inhibitors — Medicines such as rivaroxaban, apixaban and edoxaban bind factor Xa and inhibit it. As a result less thrombin and less fibrin are formed. Source 7

Sources

1. Palta S, Saroa R, Palta A. Overview of the coagulation system. Indian J Anaesth 2014 · PubMed 25535411
2. Weisel JW, Litvinov RI. Fibrin Formation, Structure and Properties. Subcell Biochem 2017 · PubMed 28101869
3. Muszbek L, Bereczky Z, Bagoly Z et al. Factor XIII: a coagulation factor with multiple plasmatic and cellular functions. Physiol Rev 2011 · PubMed 21742792
4. Chapin JC, Hajjar KA. Fibrinolysis and the control of blood coagulation. Blood Rev 2015 · PubMed 25294122
5. Adam SS, Key NS, Greenberg CS. D-dimer antigen: current concepts and future prospects. Blood 2009 · PubMed 19008457
6. Bandyopadhyay PK. Vitamin K-dependent gamma-glutamylcarboxylation: an ancient posttranslational modification. Vitam Horm 2008 · PubMed 18374194
7. Chan NC, Weitz JI. Antithrombotic Agents. Circ Res 2019 · PubMed 30702990

Related pathways

• Antiphospholipid antibodies — prothrombin
• Troponin and NT-proBNP — clearance
• Gluten antibodies — Glutamat, Glutamin

As of 2026-10-05. Draft written by Claude to schema v2; sources checked in PubMed; expert approval pending
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