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Fibrinogen is a clotting factor and acute phase reactant. Elevated levels are associated with cardiovascular disease, peripheral artery disease, and stroke. Fibrinogen is also considered a biomarker of inflammation. Elevated levels are also seen with infection, tissue damage, and neurological disorders. Low levels are associated with clotting disorders and may be observed with compromised hepatic function as it is produced in the liver.
Standard Range: 175 - 425 mg/dL (5.14 - 12.50 umol/L)
The ODX Range: 175-300 mg/dL (5.15 – 8.82 umol/L)
Low levels of fibrinogen may be seen in liver dysfunction, malnutrition, advanced cancer, disseminated intravascular coagulation, and prolonged prothrombin time. Medications that reduce fibrinogen include anabolic steroids, androgens, phenobarbital, valproic acid, streptokinase, and tissue plasminogen activators. A level below 100 mg/dL may compromise hemostasis (Pagana 2021).
High levels of fibrinogen may be seen in systemic inflammation (Pahwa 2022), acute inflammation, tissue necrosis, coronary heart disease, peripheral artery disease, stroke, trauma, severe illness, acute infection, rheumatoid arthritis, cigarette smoking, significant stress or exercise, use of estrogens and oral contraceptives (Pagana 2021), and pollution (Croft 2018) Elevated fibrinogen may also be associated with compromised blood brain barrier, neurological disorders (Petersen 2018), non-alcoholic fatty liver (Yu 2018), and vascular and nonvascular mortality, especially cancer (Danesh 2005).
Fibrinogen, also called “Factor 1,” is produced in the liver and functions as an acute phase reactant and clotting factor. Although traditionally used to identify bleeding disorders, it can increase the risk of heart disease and stroke at above optimal levels and is considered a biomarker of systemic inflammation. Levels increase with tissue damage, infection, and immunological derangement. Fibrinogen itself may promote persistent low-grade inflammation (Luyendyk 2019).
Review of NHANES data revealed that elevated fibrinogen was associated with elevated CRP and GGT and was considered a direct link between having cardiovascular disease and dying from it (Pieters 2021).
Further evaluation of the NHANES Linked Mortality Cohort found that higher fibrinogen was associated with increased mortality. Individuals with the lowest baseline fibrinogen of 118-320 mg/dL (3.5-9.4 umol/L) had the lowest cardiovascular and overall mortality compared to those with a fibrinogen greater than 320 mg/dL (9.4 umol/L). Mortality risk increased as fibrinogen increased with the highest risk being associated with a fibrinogen of 420-993 mg/dL (12.35-29.19 umol/L). Those with higher fibrinogen also tended to have higher CRP, blood pressure, total and LDL cholesterol, and triglycerides; be diabetic or hypertensive; have poorer diet quality; smoke; and either drank heavily or not at all (Liu 2020). Fibrinogen quartiles in the study were as follows: lowest, 118 to less than 321 mg/dL; second, 321 to less than 370 mg/dL; third, 370 to less than 420 mg/dL; and highest, 420–993 mg/dL. Researchers note that the quality of the diet will modify the associated between CRP and CVD mortality.
In individuals with established coronary artery disease, fibrinogen levels 280 mg/dL (8.23 umol/L) or above were independently associated with a significantly increased risk of major adverse cardiovascular events (MACEs) in the two years following nonemergent percutaneous coronary intervention (Ang 2017). An earlier meta-analysis of 18 long-term prospective studies had demonstrated that a higher mean fibrinogen of 350 versus 450 mg/dL (10.3 versus 7.4 umol/L) was significantly associated with increased CHD (Danesh 1998).
A 2005 meta-analysis of 31 prospective studies confirmed increased cardiovascular risk as fibrinogen levels increased The analysis included 154,211 subjects with a baseline fibrinogen below 562 mg/dL (16.52 umol/L) and no known coronary artery disease or stroke history. Results revealed that for every 100 mg/dL (2.94 umol/L) increase in fibrinogen above baseline, risk of coronary heart disease and stroke increased at least 1.8-fold (Danesh 2005).
Air pollution is associated with increased fibrinogen, including in those with cardiovascular disease. In one study of 135 myocardial infarction patients, fibrinogen levels increased 3.1% for each 5.6 ug/m3 rise in particulate matter pollution. However, that increase was blunted and reduced to 0.9% in subjects with a higher percentage of serum omega-3 fatty acids from fish oil (over 5.12%), but not from omega-3 alpha-linolenic acid, a precursor to long-chain omega-3s EPA and DHA (Croft 2018).
Fibrinogen and its conversion to fibrin may also trigger inflammation and scarring in the brain, activate microglia and macrophages, and promote cognitive decline, especially in the presence of a compromised blood brain barrier. Research suggests it may play a role in neurological disorders such as Alzheimer’s, multiple sclerosis, brain trauma, and neurological injury in susceptible individuals (Petersen 2018).
Ang, Lawrence et al. “Elevated Baseline Serum Fibrinogen: Effect on 2-Year Major Adverse Cardiovascular Events Following Percutaneous Coronary Intervention.” Journal of the American Heart Association vol. 6,11 e006580. 18 Nov. 2017, doi:10.1161/JAHA.117.006580
Croft, Daniel et al. “Do elevated blood levels of omega-3 fatty acids modify effects of particulate air pollutants on fibrinogen?.” Air quality, atmosphere, & health vol. 11,7 (2018): 791-799. doi:10.1007/s11869-018-0586-0
Danesh, J et al. “Association of fibrinogen, C-reactive protein, albumin, or leukocyte count with coronary heart disease: meta-analyses of prospective studies.” JAMA vol. 279,18 (1998): 1477-82. doi:10.1001/jama.279.18.1477
Danesh J, Lewington S, Thompson SG, et al. Plasma fibrinogen level and the risk of major cardiovascular diseases and nonvascular mortality: an individual participant meta-analysis. JAMA. 2005 Oct 12;294(14):1799-809.
Liu, Junxiu et al. “Associations of C-reactive protein and fibrinogen with mortality from all-causes, cardiovascular disease and cancer among U.S. adults.” Preventive medicine vol. 139 (2020): 106044. doi:10.1016/j.ypmed.2020.106044
Pagana, Kathleen Deska, et al. Mosby's Diagnostic and Laboratory Test Reference. 15th ed., Mosby, 2021.
Pahwa, Roma, et al. “Chronic Inflammation.” StatPearls, StatPearls Publishing, 8 August 2022.
Pieters, Marlien et al. “Biomarker association with cardiovascular disease and mortality - The role of fibrinogen. A report from the NHANES study.” Thrombosis research vol. 198 (2021): 182-189. doi:10.1016/j.thromres.2020.12.009