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{{Short description|Fibrin degradation product present in the blood after a thrombus}}

'''D-dimer''' (or '''D dimer''') is a [[Dimer_(chemistry)|dimer]] that is a [[fibrin degradation product]] (FDP), a small protein fragment present in the blood after a [[thrombus|blood clot]] is degraded by [[fibrinolysis]]. It is so named because it contains two D fragments of the [[fibrin]] protein joined by a [[cross-link]], hence forming a [[protein dimer]].<ref name="Asakura">{{cite journal | last1=Asakura | first1=Hidesaku | last2=Ogawa | first2=Haruhiko | title=COVID-19-associated coagulopathy and disseminated intravascular coagulation | journal=International Journal of Hematology | volume=113 | issue=1 | year=2020 | issn=0925-5710 | pmid=33161508 | pmc=7648664 | doi=10.1007/s12185-020-03029-y | pages=45–57}}</ref>

D-dimer concentration may be determined by a [[blood test]] to help diagnose [[thrombosis]].<ref name="khan">{{cite journal | last1=Khan | first1=Faizan | last2=Tritschler | first2=Tobias | last3=Kahn | first3=Susan R | last4=Rodger | first4=Marc A | title=Venous thromboembolism | journal=The Lancet | year=2021 | volume=398 | issue=10294 | pages=64–77 | issn=0140-6736 | doi=10.1016/s0140-6736(20)32658-1 |pmid=33984268| s2cid=234497047 }}</ref> Since its introduction in the 1990s, it has become an important test performed in people with suspected thrombotic disorders, such as [[venous thromboembolism]].<ref name=khan/><ref name="ponti">{{cite journal | last1=Ponti | first1=G | last2=Maccaferri | first2=M | last3=Ruini | first3=C | last4=Tomasi | first4=A | last5=Ozben | first5=T | title=Biomarkers associated with COVID-19 disease progression. | journal=Critical Reviews in Clinical Laboratory Sciences | volume=57 | issue=6 | year=2020 | issn=1040-8363 | pmid=32503382 | pmc=7284147 | doi=10.1080/10408363.2020.1770685 | pages=389–399}}</ref> While a negative result practically rules out thrombosis, a positive result can indicate thrombosis but does not exclude other potential causes.<ref name=ponti/> Its main use, therefore, is to exclude [[Thromboembolism|thromboembolic]] disease where the probability is low.<ref name="Asakura" /><ref name=khan/>

D-dimer levels are used as a predictive [[biomarker]] for the blood disorder [[disseminated intravascular coagulation]] and in the coagulation disorders associated with [[Coronavirus disease 2019|COVID-19 infection]].<ref name="Asakura" /><ref name=ponti/> A four-fold increase in the protein is an indicator of poor prognosis in people hospitalized with [[COVID-19]].<ref name="Asakura" /><ref name=ponti/><ref>{{cite journal |last1=Velavan |first1=Thirumalaisamy P. |last2=Meyer |first2=Christian G. |title=Mild versus severe COVID-19: laboratory markers |journal=International Journal of Infectious Diseases |date=25 April 2020 |volume=95 |pages=304–307 |doi=10.1016/j.ijid.2020.04.061 |pmc=7194601 |pmid=32344011 |url=https://www.ijidonline.com/article/S1201-9712(20)30277-0/fulltext#%20 |access-date=25 April 2020|doi-access=free }}</ref>

== Principles ==
[[Image:D-dimer.png|right|framed|'''D-dimer formation.''' Shown are ''[[fibrinogen]]'', with its one ''E'' domain and two ''D'' domains, acted upon in cascade, by the following [[enzyme]]s: ''[[Thrombin]]'', to create a ''mesh of fibrin'' protofibrils; [[Factor XIII]] to ''crosslink the fibrin mesh'' (linking protofibril D domains), the scaffold for [[blood clot|clot]] formation; ''[[Plasmin]]'', whose action in [[fibrinolysis]] produces [[fibrin degradation products]] (''FDPs''), the smallest of which are ''D-dimers'', protein fragments with one E and two crosslinked D domains.<ref name="Asakura" /><ref name=wells/>]]
[[Coagulation]], the formation of a blood clot or [[thrombus]], occurs when the proteins of the [[coagulation cascade]] are activated, either by contact with a damaged blood vessel wall and exposure to collagen in the tissue space (intrinsic pathway) or by activation of [[factor VII]] by [[tissue factor|tissue activating factors]] (extrinsic pathway). Both pathways lead to the generation of [[thrombin]], an enzyme that turns the soluble blood protein [[fibrin]]ogen into fibrin, which aggregates into protofibrils. Another thrombin-generated enzyme, [[factor XIII]], then crosslinks the fibrin protofibrils at the D fragment site, leading to the formation of an insoluble gel that serves as a scaffold for blood clot formation.<ref name="Asakura" />

The circulating enzyme [[plasmin]], the main enzyme of [[fibrinolysis]], cleaves the fibrin gel in a number of places. The resultant fragments, "high molecular weight polymers", are digested several times more by plasmin to lead to intermediate and then to small polymers ([[fibrin degradation product]]s or FDPs). The cross-link between two D fragments remains intact, however, and these are exposed on the surface when the fibrin fragments are sufficiently digested. The structure of D-dimer is either a 180&nbsp;[[Dalton (unit)|kDa]]<ref name="KoganMukharyamova2016">{{cite journal | vauthors = Kogan AE, Mukharyamova KS, Bereznikova AV, Filatov VL, Koshkina EV, Bloshchitsyna MN, Katrukha AG | title = Monoclonal antibodies with equal specificity to D-dimer and high-molecular-weight fibrin degradation products | journal = Blood Coagulation & Fibrinolysis | volume = 27 | issue = 5 | pages = 542–50 | date = July 2016 | pmid = 26656897 | pmc = 4935535 | doi = 10.1097/MBC.0000000000000453 }}</ref> or 195 kDa<ref name="OlsonCunningham2013">{{cite journal | vauthors = Olson JD, Cunningham MT, Higgins RA, Eby CS, Brandt JT | title = D-dimer: simple test, tough problems | journal = Archives of Pathology & Laboratory Medicine | volume = 137 | issue = 8 | pages = 1030–8 | date = August 2013 | pmid = 23899057 | doi = 10.5858/arpa.2012-0296-CP }}</ref> molecule of two D domains, or a 340 kDa<ref name="OlsonCunningham2013"/> molecule of two D domains and one E domain.<ref name="Asakura" /> The [[biological half-life|half-life]] of D-dimer in blood is approximately 6 to 8&nbsp;hours.<ref name="pmid20213258">{{cite journal | vauthors = Lippi G, Cervellin G, Franchini M, Favaloro EJ | title = Biochemical markers for the diagnosis of venous thromboembolism: the past, present and future | journal = J Thromb Thrombolysis | volume = 30 | issue = 4 | pages = 459–71 | date = November 2010 | pmid = 20213258 | doi = 10.1007/s11239-010-0460-x | s2cid = 23806848 | url = }}</ref>

D-dimers are not normally present in human blood plasma, except when the coagulation system has been activated, for instance, because of the presence of [[thrombosis]] or [[disseminated intravascular coagulation]]. The D-dimer assay depends on the binding of a [[monoclonal antibody]] to a particular [[epitope]] on the D-dimer fragment. Several detection kits are commercially available; all of them rely on a different monoclonal antibody against D-dimer. For some of these, the area of the D-dimer to which the antibody binds is known. The binding of the antibody is then measured quantitatively by one of various laboratory methods.<ref name="Asakura" />

== Indications ==
D-dimer testing is of clinical use when there is a suspicion of [[deep venous thrombosis]] (DVTl), [[pulmonary embolism]] (PE) or [[disseminated intravascular coagulation]] (DIC).<ref name="Asakura" /><ref name=ponti/>

For DVT and PE, there are possible various scoring systems that are used to determine the ''a priori'' clinical probability of these diseases; the best-known is the [[Deep vein thrombosis#Diagnosis|Wells score]].<ref name="wells">{{cite journal | vauthors = Wells PS, Anderson DR, Rodger M, Forgie M, Kearon C, Dreyer J, Kovacs G, Mitchell M, Lewandowski B, Kovacs MJ | display-authors = 6 | title = Evaluation of D-dimer in the diagnosis of suspected deep-vein thrombosis | journal = The New England Journal of Medicine | volume = 349 | issue = 13 | pages = 1227–35 | date = September 2003  | doi = 10.1056/NEJMoa023153|pmid=14507948| doi-access = free }}</ref>
* For a high score, or pretest probability, a D-dimer will make little difference and [[anticoagulant]] therapy will be initiated regardless of test results, and additional testing for DVT or pulmonary embolism may be performed.
* For a moderate or low score, or pretest probability:{{cn|date=October 2022}}
** A negative D-dimer test will virtually rule out thromboembolism:<ref name="wells" /> the degree to which the D-dimer reduces the probability of thrombotic disease is dependent on the test properties of the specific test used in the clinical setting: most available D-dimer tests with a negative result will reduce the probability of thromboembolic disease to less than 1% if the pretest probability is less than 15-20%. Chest computed tomography (CT angiography) should not be used to evaluate [[pulmonary embolism]] for persons with negative results of a D-dimer assay.<ref name="ACCPandATSfive">{{Citation |author1 = American College of Chest Physicians |author1-link = American College of Chest Physicians |author2 = American Thoracic Society |author2-link = American Thoracic Society |date = September 2013 |title = Five Things Physicians and Patients Should Question |publisher = American College of Chest Physicians and American Thoracic Society |work = [[Choosing Wisely]]: an initiative of the [[ABIM Foundation]] |url = http://www.choosingwisely.org/doctor-patient-lists/american-college-of-chest-physicians-and-american-thoracic-society/ |access-date = 6 January 2013}}.</ref> A low pretest probability is also valuable in ruling out PE.<ref>{{cite journal | vauthors = Crawford F, Andras A, Welch K, Sheares K, Keeling D, Chappell FM | title = D-dimer test for excluding the diagnosis of pulmonary embolism | journal = The Cochrane Database of Systematic Reviews | issue = 8 | article-number = CD010864 | date = August 2016 | volume = 2016 | pmid = 27494075 | pmc = 6457638 | doi = 10.1002/14651858.CD010864.pub2 | editor-last = Cochrane Vascular Group }}</ref>
** If the D-dimer reads high, then further testing ([[medical ultrasonography|ultrasound]] of the leg veins or lung [[scintigraphy]] or [[CTPA|CT scanning]]) is required to confirm the presence of [[thrombus]].  [[Anticoagulant]] therapy may be started at this point or withheld until further tests confirm the diagnosis, depending on the clinical situation.

In some hospitals, they are measured by laboratories after a form is completed showing the probability score and only if the probability score is low or intermediate. This reduces the need for unnecessary tests in those who are high-probability.<ref>{{cite journal | vauthors = Rathbun SW, Whitsett TL, Vesely SK, Raskob GE | title = Clinical utility of D-dimer in patients with suspected pulmonary embolism and nondiagnostic lung scans or negative CT findings | journal = Chest | volume = 125 | issue = 3 | pages = 851–5 | date = March 2004 | pmid = 15006941 | pmc = 1215466 | doi = 10.1378/chest.125.3.851 }}</ref> Performing the D-dimer test first can avoid a significant proportion of imaging tests and is less invasive. Since the D-dimer can exclude the need for imaging, [[Specialty (medicine)|specialty]] [[professional organizations]] recommend that physicians use D-dimer testing as an initial diagnostic.<ref name="ACPfive">{{Citation |author1 = American College of Physicians |author1-link = Consumer Reports |others = presented by [[ABIM Foundation]] |title = Five Things Physicians and Patients Should Question |publisher = [[American College of Physicians]] |work = Choosing Wisely |url = http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_College_Phys.pdf |access-date = August 14, 2012 |archive-url = https://web.archive.org/web/20120624075449/http://choosingwisely.org/wp-content/uploads/2012/04/5things_12_factsheet_Amer_College_Phys.pdf |archive-date = June 24, 2012 }}</ref><ref name="ACEPembolism">{{cite journal | vauthors = Fesmire FM, Brown MD, Espinosa JA, Shih RD, Silvers SM, Wolf SJ, Decker WW | title = Critical issues in the evaluation and management of adult patients presenting to the emergency department with suspected pulmonary embolism | journal = Annals of Emergency Medicine | volume = 57 | issue = 6 | pages = 628–652.e75 | date = June 2011 | pmid = 21621092 | doi = 10.1016/j.annemergmed.2011.01.020 | author8 = American College of Emergency Physicians | doi-access = free }}</ref><ref name="ECSpulemb">{{cite journal | vauthors = Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galiè N, Pruszczyk P, Bengel F, Brady AJ, Ferreira D, Janssens U, Klepetko W, Mayer E, Remy-Jardin M, Bassand JP | display-authors = 6 | title = Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC) | journal = European Heart Journal | volume = 29 | issue = 18 | pages = 2276–315 | date = September 2008 | pmid = 18757870 | doi = 10.1093/eurheartj/ehn310 | doi-access = free }}</ref><ref name="AAFPthrombo">{{cite journal | vauthors = Qaseem A, Snow V, Barry P, Hornbake ER, Rodnick JE, Tobolic T, Ireland B, Segal J, Bass E, Weiss KB, Green L, Owens DK | display-authors = 6 | title = Current diagnosis of venous thromboembolism in primary care: a clinical practice guideline from the American Academy of Family Physicians and the American College of Physicians | journal = Annals of Family Medicine | volume = 5 | issue = 1 | pages = 57–62 | year = 2007 | pmid = 17261865 | pmc = 1783928 | doi = 10.1370/afm.667 }}</ref>

== Interpretation ==

=== Reference ranges ===
The following are [[reference range]]s for D-dimer:<ref>[http://www.perinatology.com/Reference/Reference%20Ranges/D-Dimer.htm Reference Values During Pregnancy] at perinatology.com. Retrieved October 2014.</ref>
{|class="wikitable"
! Units !! Nonpregnant <br />adult !! First [[Pregnancy|trimester]] !! Second trimester !! Third trimester
|-
| mg/L or μg/mL || < 0.5 || 0.05 - 0.95 || 0.32 - 1.29 || 0.13 -1.7
|-
| μg/L or ng/mL || < 500|| 50 - 950 || 320 - 1290 || 130 - 1700
|-
| nmol/L || < 2.7 || 0.3 - 5.2 || 1.8 - 7.1 || 0.7 - 9.3
|}

D-dimer increases with age. It has therefore been suggested to use a cutoff equal to patient's age in years × 10 μg/L (or x 0.056 nmol/L) for patients aged over 50 years for the suspicion of venous thromboembolism (VTE), as it decreases the [[false positive]] rate without substantially increasing the [[false negative]] rate.<ref>{{cite journal | vauthors = Urban K, Kirley K, Stevermer JJ | title = PURLs: It's time to use an age-based approach to D-dimer | journal = The Journal of Family Practice | volume = 63 | issue = 3 | pages = 155–8 | date = March 2014 | pmid = 24701602 | pmc = 4042909 }}</ref><ref>{{cite journal | vauthors = Raja AS, Greenberg JO, Qaseem A, Denberg TD, Fitterman N, Schuur JD | title = Evaluation of Patients With Suspected Acute Pulmonary Embolism: Best Practice Advice From the Clinical Guidelines Committee of the American College of Physicians | journal = Annals of Internal Medicine | volume = 163 | issue = 9 | pages = 701–11 | date = November 2015 | pmid = 26414967 | doi = 10.7326/M14-1772 | doi-access = free }}</ref>

{{Anchor|FEU}}An alternative measurement of D-dimer is in fibrinogen equivalent units (FEU). The molecular weight of the fibrinogen molecule is about twice the size of the D-dimer molecule, and therefore 1.0 mcg/mL FEU is equivalent to 0.5 mcg/mL of d-dimer.<ref>{{cite web|url=http://education.questdiagnostics.com/faq/FAQ149|title=Clinical Education Center|website=Quest Diagnostics}} Document FAQS.149 Version: 3 effective 07/23/2019 to present</ref>

=== Thrombotic disease ===
Various kits have a 93 to 95% [[Sensitivity and specificity#Sensitivity|sensitivity]] (true positive rate). For hospitalized patients, one study found the [[Sensitivity and specificity#Specificity|specificity]] to be about 50% (related to false positive rate) in the diagnosis of thrombotic disease.<ref>{{cite journal | vauthors = Schrecengost JE, LeGallo RD, Boyd JC, Moons KG, Gonias SL, Rose CE, Bruns DE | title = Comparison of diagnostic accuracies in outpatients and hospitalized patients of D-dimer testing for the evaluation of suspected pulmonary embolism | journal = Clinical Chemistry | volume = 49 | issue = 9 | pages = 1483–90 | date = September 2003 | pmid = 12928229 | doi = 10.1373/49.9.1483 | doi-access = free }}</ref>
* [[False positive]] readings can be due to various causes: [[liver]] disease, high [[rheumatoid factor]], [[inflammation]], [[cancer|malignancy]], [[Physical trauma|trauma]], [[pregnancy]], recent [[surgery]] as well as advanced age.<ref>{{cite journal | vauthors = Kabrhel C, Mark Courtney D, Camargo CA, Plewa MC, Nordenholz KE, Moore CL, Richman PB, Smithline HA, Beam DM, Kline JA | display-authors = 6 | title = Factors associated with positive D-dimer results in patients evaluated for pulmonary embolism | journal = Academic Emergency Medicine | volume = 17 | issue = 6 | pages = 589–97 | date = June 2010 | pmid = 20624138 | pmc = 3538031 | doi = 10.1111/j.1553-2712.2010.00765.x }}</ref>
* [[False negative]] readings can occur if the sample is taken either too early after thrombus formation or if testing is delayed for several days. Additionally, the presence of anti-coagulation can render the test negative because it prevents thrombus extension. The anti-coagulation medications [[dabigatran]] and [[rivaroxaban]] decrease D-dimer levels but do not interfere with the D-dimer assay.<ref name="BaglinKeeling2012">{{cite journal | vauthors = Baglin T, Keeling D, Kitchen S | title = Effects on routine coagulation screens and assessment of anticoagulant intensity in patients taking oral dabigatran or rivaroxaban: guidance from the British Committee for Standards in Haematology | journal = British Journal of Haematology | volume = 159 | issue = 4 | pages = 427–9 | date = November 2012 | pmid = 22970737 | doi = 10.1111/bjh.12052 | doi-access = free }}</ref>
* False values may be obtained if the specimen collection tube is not sufficiently filled (false low value if underfilled and false high value if overfilled). This is due to the dilutional effect of the anticoagulant (the blood must be collected in a 9:1 blood to anticoagulant ratio).
* Likelihood ratios are derived from sensitivity and specificity to adjust pretest probability.

In interpretation of the D-dimer, for patients over age 50, a value of (patient's age) × 10 μg/L may be abnormal.<ref name="pmid22072293">{{cite journal | vauthors = van Es J, Mos I, Douma R, Erkens P, Durian M, Nizet T, van Houten A, Hofstee H, ten Cate H, Ullmann E, Büller H, Huisman M, Kamphuisen PW | display-authors = 6 | title = The combination of four different clinical decision rules and an age-adjusted D-dimer cut-off increases the number of patients in whom acute pulmonary embolism can safely be excluded | journal = Thrombosis and Haemostasis | volume = 107 | issue = 1 | pages = 167–71 | date = January 2012 | pmid = 22072293 | doi = 10.1160/TH11-08-0587 | s2cid = 4832019 | hdl = 1765/74645 | hdl-access = free }}</ref><ref name="pmid20354012">{{cite journal | vauthors = Douma RA, le Gal G, Söhne M, Righini M, Kamphuisen PW, Perrier A, Kruip MJ, Bounameaux H, Büller HR, Roy PM | display-authors = 6 | title = Potential of an age adjusted D-dimer cut-off value to improve the exclusion of pulmonary embolism in older patients: a retrospective analysis of three large cohorts | journal = BMJ | volume = 340 | article-number = c1475 | date = March 2010 | pmid = 20354012 | pmc = 2847688 | doi = 10.1136/bmj.c1475 }}</ref>

== History ==
D-dimer was originally identified, described and named in the 1970s ([https://www.sciencedirect.com/sdfe/pdf/download/eid/1-s2.0-026894999390039X/first-page-pdf Fibrinolysis, Dr P J Gaffney]) and found its diagnostic application in the 1990s.<ref name="Asakura" /><ref name=wells/>

== References ==
{{reflist}}

== External links ==
* [http://labtestsonline.org/understanding/analytes/d-dimer/tab/test D-dimer] - Lab Tests Online

{{Coagulation cascade}}
{{Myeloid blood tests}}

[[Category:Chemical pathology]]
[[Category:Fibrinolytic system]]
[[Category:Blood tests]]