Lab result explainedBlood count (CBC)Last updated November 10, 2026

Fibrinogen blood test: normal range and what high or low fibrinogen (factor I) means

Fibrinogen · Coagulation panel (PT/INR, PTT, fibrinogen) · reported in mg/dL on most US reports (some labs use g/L; 1 g/L = 100 mg/dL)

Fibrinogen, also called coagulation factor I, is the protein in your blood that is converted into fibrin, the mesh that holds a clot together. It is made by the liver and circulates in large amounts: a normal level is about 200 to 400 mg/dL (2 to 4 g/L), with some variation between laboratories. The fibrinogen blood test is ordered to investigate bleeding, to check for disseminated intravascular coagulation (DIC) in seriously ill or bleeding patients, to monitor massive hemorrhage, and sometimes as a marker of inflammation and cardiovascular risk.

A low fibrinogen is the result that matters most acutely. Below about 150 mg/dL bleeding becomes harder to control during surgery, trauma or childbirth, and below 100 mg/dL spontaneous bleeding can occur. The usual reasons are consumption in DIC, dilution and loss in major hemorrhage, failure of production in advanced liver disease, or a rare inherited deficiency. A high fibrinogen is far more common and far less urgent: fibrinogen is an acute-phase protein, so it rises with infection, inflammation, cancer, smoking, obesity and pregnancy, where values of 400 to 650 mg/dL are normal by the third trimester.

Persistently high fibrinogen in someone who is well is also a modest independent marker of cardiovascular risk. Large pooled analyses show that each 100 mg/dL (1 g/L) increase is associated with roughly 1.8 times the risk of coronary heart disease after accounting for other risk factors, though there is no treatment aimed at fibrinogen itself; the levers are the familiar ones of not smoking, weight, activity and treating the inflammation behind it.

Fibrinogen at a glance

What it is: factor I, the liver-made clotting protein that thrombin turns into fibrin; also an acute-phase protein that rises with inflammation.
Normal: about 200–400 mg/dL (2.0–4.0 g/L); some labs use 150–450. Pregnancy raises it to 400–650 mg/dL by the third trimester.
High fibrinogen: infection, inflammation, cancer, smoking, obesity, pregnancy, estrogen, diabetes, kidney disease; values over about 350–400 are linked with higher cardiovascular risk.
Low fibrinogen: DIC, massive bleeding, advanced liver disease, thrombolytic drugs, L-asparaginase, or inherited deficiency; under 150 mg/dL raises bleeding risk, under 100 is critical.
In major bleeding (trauma, childbirth, surgery), replacement is usually considered when fibrinogen falls below 150–200 mg/dL.
Next step: for a high value, treat the cause and address smoking, weight and activity; for a low value, urgent assessment of bleeding, DIC and liver function.

Have your whole report? Paste it into the free Lab Explainer

Every marker explained in plain language, in context with the others, with questions to bring to your appointment. No account needed.

What Fibrinogen measures

Fibrinogen is a large soluble protein (340 kDa) produced by liver cells, with a normal half-life of about four days. In the final step of clotting, thrombin clips small peptides off fibrinogen, the remaining fibrin monomers polymerise into strands, and factor XIII cross-links them into a stable mesh that traps platelets and red cells. Fibrinogen also binds platelets to each other during platelet aggregation, so it is central to both arms of hemostasis. Because it is abundant and the last common step in the cascade, very low levels prolong the PT, PTT and thrombin time together.

The standard test is the Clauss fibrinogen assay, which measures function: diluted plasma is clotted with a high dose of thrombin and the clotting time is converted to a concentration against a calibration curve. Some analyzers instead derive a fibrinogen estimate from the optical change during the PT (PT-derived fibrinogen), which tends to over-read in inflammation and under certain anticoagulants. A separate immunological assay measures fibrinogen antigen (the amount of protein regardless of function); a low activity with a normal antigen points to dysfibrinogenemia, where the protein is present but does not work properly.

Fibrinogen responds to the same interleukin-6 signal that drives C-reactive protein, so it rises two to three fold within one to three days of infection, injury or inflammation and comes down more slowly than CRP because of its longer half-life. No fasting is needed. The citrate tube must be filled correctly, and heparin contamination or very high levels of fibrin degradation products can falsely lower a Clauss result.

Normal range for Fibrinogen

Reference ranges vary between labs and by age, sex and pregnancy. Use the range printed on your own report.

Group	Typical range (mg/dL on most US reports (some labs use g/L; 1 g/L = 100 mg/dL))	Notes
Normal, adults	About 200–400 mg/dL (2.0–4.0 g/L)	Some labs use 150–450 or 180–350. Values vary with age, inflammation and assay; use the range on your report.
Borderline high	400–500 mg/dL	Common with smoking, obesity, diabetes, oral estrogen, older age, mild infection or inflammation, and in pregnancy.
High	Above 500 mg/dL	Acute infection, major inflammation or tissue injury, active cancer, nephrotic syndrome, late pregnancy. Can exceed 700–900 mg/dL in severe inflammation.
Cardiovascular risk association	Persistently above about 350–400 mg/dL	Each 100 mg/dL higher is associated with roughly 1.8× the risk of coronary heart disease in pooled cohort studies. A risk marker, not a treatment target.
Mildly low	150–200 mg/dL	Early consumption, dilution, liver disease, or mild inherited deficiency. Bleeding risk starts to rise with surgery or hemorrhage; in postpartum hemorrhage a value below 200 predicts severe bleeding.
Low	100–150 mg/dL	Meaningful bleeding risk during surgery, trauma or childbirth. Replacement with cryoprecipitate or fibrinogen concentrate is usually considered below 150–200 in active major bleeding.
Critically low	Below 100 mg/dL (many labs flag below 50–100)	DIC, massive hemorrhage, severe liver failure or afibrinogenemia. Spontaneous bleeding can occur; prolongs PT, PTT and thrombin time.
Pregnancy, third trimester	400–650 mg/dL	A physiological rise. A 'normal' 250 mg/dL at term is relatively low and, with heavy bleeding, is treated as significant.
Newborns	Roughly 150–350 mg/dL	Similar to or slightly below adult values; functional fibrinogen matures over the first months.

High fibrinogen

A high fibrinogen almost always means inflammation. Like CRP, fibrinogen is an acute-phase protein, so infection, surgery, injury, autoimmune disease, inflammatory bowel disease and cancer push it above 400 mg/dL, and severe inflammation can take it above 700. A raised fibrinogen alongside a raised CRP and ESR simply confirms the inflammatory response; it does not say where the inflammation is or what is causing it. In pregnancy, the rise is physiological and values up to about 650 mg/dL at term are expected.

When fibrinogen runs persistently in the 400 to 500 range in someone who feels well, the usual drivers are smoking, excess body fat (especially abdominal), insulin resistance and diabetes, oral estrogen, chronic kidney disease, periodontal disease and older age. This chronic low-grade elevation is the reason fibrinogen appears in cardiovascular risk research: it thickens blood, promotes platelet aggregation and fibrin deposition in plaques, and each 100 mg/dL increase is associated with roughly 1.8 times the risk of coronary heart disease and a higher risk of stroke in pooled analyses of over 150,000 people.

High fibrinogen is not itself treated and is not a reason for anticoagulation. It is interpreted as a signal to find and treat the inflammation, and in otherwise healthy people as one more reason to act on smoking, weight, activity and blood sugar. Very high values do slightly raise plasma viscosity and ESR, which is why an unexpectedly high ESR is sometimes explained by fibrinogen alone.

Common causes

Acute infection and tissue injury
Bacterial and viral infections, pneumonia, cellulitis, sepsis in its early phase, surgery, burns and fractures raise fibrinogen 2 to 3 fold within 1 to 3 days, peaking around day 3 to 5 and falling over 1 to 2 weeks as the trigger resolves.
Chronic inflammatory and autoimmune disease
Rheumatoid arthritis, lupus, vasculitis, inflammatory bowel disease, psoriasis and polymyalgia rheumatica raise fibrinogen in proportion to disease activity, alongside CRP and ESR.
Smoking
Smokers have fibrinogen around 20 to 40 mg/dL higher than non-smokers, in proportion to the number of cigarettes, through airway and vascular inflammation. Levels fall after quitting, with much of the drop in the first weeks to months.
Obesity, insulin resistance and type 2 diabetes
Visceral fat releases interleukin-6, which drives hepatic fibrinogen production. People with obesity or metabolic syndrome commonly run 350 to 450 mg/dL, and the level falls with weight loss.
Pregnancy and estrogen
Fibrinogen rises steadily from the first trimester to 400 to 650 mg/dL at term as part of the preparation for delivery. Combined oral contraceptives and oral menopausal hormone therapy raise it modestly.
Cancer
Many solid tumors (lung, pancreatic, ovarian, stomach, colorectal) and lymphoma provoke an acute-phase response and increased clotting activity; a high fibrinogen with a high D-dimer is common in active cancer and is part of the reason cancer increases clot risk.
Kidney disease and nephrotic syndrome
Chronic kidney disease carries chronic low-grade inflammation, and nephrotic syndrome drives the liver to overproduce fibrinogen (along with cholesterol) in response to protein loss, contributing to the high clot risk in these patients.
Older age
Fibrinogen rises by roughly 10 to 20 mg/dL per decade of adult life, so values near 400 are common in healthy people over 70.
Heart attack, stroke and peripheral artery disease
Acute vascular events raise fibrinogen as part of the inflammatory response, and people with established atherosclerosis tend to have chronically higher levels, which predict further events.

Symptoms that can go with it

Often none: a mildly raised fibrinogen from smoking, weight or age causes no symptoms of its own
Fever, chills, pain or swelling at the site of an infection or injury
Joint pain and morning stiffness, abdominal pain or bloody diarrhea with inflammatory disease
Unexplained weight loss, night sweats or a new lump when cancer is the driver
Leg swelling and frothy urine with nephrotic syndrome
Chest pain, breathlessness or leg pain on walking in people with the cardiovascular disease that high fibrinogen is linked to

Low fibrinogen

A low fibrinogen means your blood has less of the raw material for clots, and the lower it is the harder bleeding is to stop. Levels between 150 and 200 mg/dL are rarely a problem day to day but matter during surgery, trauma or childbirth; between 100 and 150 the risk of significant bleeding rises clearly; below 100 mg/dL spontaneous bruising, mucosal bleeding and prolonged bleeding from wounds can occur, and the PT, PTT and thrombin time are all prolonged. Most labs treat a value under 100 (some under 50) as a critical result.

In hospital, the usual question behind a low fibrinogen is consumption or loss. Disseminated intravascular coagulation uses up fibrinogen and platelets at the same time, so a falling fibrinogen with low platelets, a prolonged PT and a very high D-dimer in someone with sepsis, trauma, leukemia or an obstetric emergency points to DIC. Massive bleeding of any cause, including postpartum hemorrhage, removes fibrinogen faster than the liver can replace it, and fibrinogen is the first factor to reach critically low levels; in postpartum hemorrhage a value under 200 mg/dL predicts progression to severe bleeding, which is why obstetric teams check it early and replace it promptly.

Outside those emergencies, a low fibrinogen points to the liver or to an inherited condition. Advanced cirrhosis and acute liver failure reduce production; thrombolytic drugs such as alteplase and the leukemia drug L-asparaginase lower it as a known effect; and the rare congenital disorders (afibrinogenemia, hypofibrinogenemia and dysfibrinogenemia, together about 1 to 2 per million) cause lifelong low or dysfunctional fibrinogen with bleeding and, paradoxically, sometimes clotting.

Common causes

Disseminated intravascular coagulation (DIC)
Widespread activation of clotting in sepsis, major trauma, burns, placental abruption, amniotic fluid embolism, acute promyelocytic leukemia or snake envenomation consumes fibrinogen. A fibrinogen under 100 mg/dL scores a point on the ISTH DIC scale; a falling trend is more telling than one value.
Massive hemorrhage and hemodilution
Major trauma, surgical bleeding and postpartum hemorrhage lose fibrinogen with the blood and dilute what remains with fluids and red cells. Fibrinogen falls below 100 before other factors do; trauma guidelines recommend replacement when it drops under 150 mg/dL.
Advanced liver disease
Cirrhosis and acute liver failure reduce synthesis and can produce an abnormal, poorly functioning fibrinogen. Levels under 100 to 150 mg/dL indicate severely impaired synthetic function and accompany a prolonged INR and low albumin.
Thrombolytic therapy
Alteplase, tenecteplase and streptokinase, given for stroke, heart attack or massive PE, activate plasmin, which breaks down fibrinogen as well as clots; levels can fall below 100 mg/dL for a day or two and are monitored when bleeding occurs.
L-asparaginase and some other medicines
L-asparaginase and pegaspargase used in acute lymphoblastic leukemia suppress hepatic fibrinogen synthesis and routinely drop levels below 100 mg/dL. High-dose valproate and some anabolic steroids lower fibrinogen modestly.
Inherited fibrinogen disorders
Afibrinogenemia (near zero, with umbilical stump bleeding in infancy and lifelong bleeding), hypofibrinogenemia (low but present) and dysfibrinogenemia (normal amount, abnormal function, with bleeding or thrombosis or neither). Diagnosed by comparing fibrinogen activity with fibrinogen antigen.
Snake bite
Venoms of many vipers and some elapids contain enzymes that consume fibrinogen, producing an undetectable level and unclottable blood within hours; this is the basis of the bedside 20-minute whole blood clotting test used in envenomation.
Laboratory artefact
Heparin in the sample, very high fibrin degradation products, an underfilled citrate tube or a very high hematocrit can falsely lower a Clauss fibrinogen; a repeat from a clean venepuncture is sometimes all that is needed.

Symptoms that can go with it

Easy bruising, nosebleeds and bleeding gums
Prolonged bleeding from cuts, drip sites, dental extractions or surgical wounds
Heavy menstrual bleeding, or heavy bleeding after childbirth
Oozing from multiple sites at once, with purpuric spots, in DIC
Blood in urine or stool, or vomiting blood
In inherited afibrinogenemia: bleeding from the umbilical stump in newborns, joint and muscle bleeds, and recurrent miscarriage
Signs of the underlying cause: fever and confusion in sepsis, jaundice and swollen abdomen in liver disease

Read it alongside

PT/INR and PTT — both become prolonged once fibrinogen falls below about 100 mg/dL; together they separate DIC and liver failure from an isolated fibrinogen problem.
Platelet count — low platelets with low fibrinogen suggests consumption (DIC, massive bleeding) or advanced liver disease with an enlarged spleen.
D-dimer — very high with a falling fibrinogen in DIC; also raised, with a high fibrinogen, in inflammation and cancer.
Thrombin time — prolonged by low or dysfunctional fibrinogen and by heparin; a quick way to confirm the fibrinogen problem is real.
Fibrinogen antigen — ordered when activity is low, to tell hypofibrinogenemia (both low) from dysfibrinogenemia (antigen normal).
CRP and ESR — move with fibrinogen in inflammation; a high ESR is sometimes due to fibrinogen alone.
Liver panel (ALT, albumin, bilirubin) — abnormal when the liver is the reason for a low fibrinogen.
Hemoglobin — a falling hemoglobin with a falling fibrinogen during bleeding signals the need for replacement.

What usually happens next

A high fibrinogen is read with CRP, ESR and your symptoms; if there is an obvious infection or injury it is simply rechecked once that has settled, usually in 2 to 4 weeks.
A persistently high value with no inflammation prompts a review of smoking, weight, blood sugar, blood pressure and lipids as part of overall cardiovascular risk; fibrinogen itself is not treated with medicines.
A low fibrinogen in hospital is repeated within hours alongside platelets, PT, PTT and D-dimer to look for DIC or ongoing bleeding, and replacement with cryoprecipitate or fibrinogen concentrate is considered if you are bleeding and the level is under 150 to 200 mg/dL.
A low fibrinogen in someone who is well is repeated from a fresh sample with a fibrinogen antigen and liver tests; a confirmed inherited disorder is referred to a hemophilia treatment center.
Questions to ask: is the level low because of consumption, loss or production; do I need a plan before surgery, dental work or pregnancy; and should family members be tested?

Diet, lifestyle and natural levers with evidence

What can move Fibrinogen once the cause is known. Nothing here replaces finding the cause.

Stop smoking

Strong evidence

Smoking is the strongest lifestyle driver of high fibrinogen: smokers run about 20 to 40 mg/dL (0.2 to 0.4 g/L) above non-smokers, in proportion to cigarettes per day. Fibrinogen falls within the first weeks of quitting and continues to decline toward non-smoker levels over the following years, which accounts for part of the fall in cardiovascular risk after stopping.

Weight loss, particularly abdominal fat

Moderate evidence

Fibrinogen correlates with BMI and waist circumference because visceral fat releases interleukin-6. Intervention studies report reductions of roughly 10 to 30 mg/dL with 5 to 10 percent weight loss, and larger falls after bariatric surgery, with CRP and plasminogen activator inhibitor falling alongside.

Regular aerobic exercise

Moderate evidence

Longitudinal and randomised studies of exercise training show fibrinogen falls by around 10 to 30 mg/dL over 3 to 12 months of regular moderate activity, with the largest reductions in people who start with high levels or who also lose weight. Physical fitness is inversely related to fibrinogen in population studies.

A single bout of hard exercise transiently raises fibrinogen and clotting activity for a day; do not test straight after a race.

Mediterranean-style diet rich in fiber

Preliminary evidence

Higher intake of fruit, vegetables, whole grains and fiber is associated with lower fibrinogen in cohort studies, and small trials of Mediterranean-style eating report modest reductions (around 5 to 10 percent) alongside falls in CRP. The effect is smaller and less consistent than for smoking cessation or weight loss.

Omega-3 fatty acids (EPA and DHA)

Preliminary evidence

Trials of fish oil at 2 to 4 g a day have reported small decreases in fibrinogen (on the order of 5 to 10 percent) in some but not all studies, with meta-analyses finding the effect inconsistent. Any benefit is likely to come from reduced inflammation rather than a direct effect on the protein.

Doses above 3 g a day add to bleeding risk, particularly with anticoagulants or antiplatelet drugs.

Nattokinase

Preliminary evidence

Small trials of this enzyme from fermented soybeans (around 2,000 fibrinolytic units a day for two months) reported falls in fibrinogen of about 7 to 10 percent, together with reductions in factors VII and VIII. The studies were small and short, and no trial has shown a clinical benefit.

Nattokinase has fibrinolytic activity and should not be combined with warfarin, DOACs, antiplatelet drugs or taken before surgery; it is not a treatment for a high fibrinogen or a substitute for prescribed anticoagulation.

When to see a clinician promptly

Bleeding that will not stop with 10 to 15 minutes of pressure, vomiting blood, black stools, or bleeding from several sites at once: emergency care, particularly if your fibrinogen is known to be low.
A fibrinogen below 100 mg/dL on any report is a critical result and needs same-day medical review even without bleeding.
Heavy bleeding after childbirth, or during pregnancy with abdominal pain: fibrinogen can fall fast and replacement may be needed urgently.
Fever, confusion, widespread bruising or purple spots with a low fibrinogen and low platelets: possible sepsis with DIC.
A low fibrinogen with jaundice, a swollen abdomen or confusion in someone with liver disease.
A high fibrinogen that stays above 500 mg/dL once an infection has cleared, especially with weight loss, night sweats or persistent fatigue.

Frequently asked questions

What is a normal fibrinogen level?

Most laboratories report a normal fibrinogen of about 200 to 400 mg/dL (2.0 to 4.0 g/L); some use 150 to 450. Levels rise with age, inflammation and pregnancy, where 400 to 650 mg/dL is normal by the third trimester. If your report is in g/L, multiply by 100 to convert to mg/dL.

What does high fibrinogen mean?

High fibrinogen almost always reflects inflammation, because fibrinogen is an acute-phase protein that rises with infection, injury, autoimmune disease and cancer. Persistent mild elevation in someone who is well is usually from smoking, excess body fat, diabetes, estrogen, kidney disease or age, and is associated with a higher cardiovascular risk. It is not treated directly; the cause is addressed.

What does low fibrinogen mean?

Low fibrinogen means your blood has less of the protein that forms clots, so bleeding is harder to stop. The common causes are consumption in DIC, loss in major bleeding, reduced production in advanced liver disease, thrombolytic or asparaginase treatment, and rarely an inherited deficiency. Below 150 mg/dL bleeding risk rises with surgery or injury; below 100 is critical.

Is a fibrinogen of 450 or 500 high?

A fibrinogen of 450 mg/dL is mildly above the usual range and is typical of smoking, obesity, a recent minor infection or pregnancy. A value of 500 is clearly raised and usually reflects an active infection, inflammation or injury, or late pregnancy. Neither needs treatment on its own; the test is usually repeated once any illness has settled, and if it stays high the usual cardiovascular risk factors are reviewed.

What fibrinogen level is dangerous?

The dangerous direction is low. Below about 150 mg/dL bleeding becomes difficult to control during surgery, trauma or childbirth, and below 100 mg/dL spontaneous bleeding can occur; most labs phone values under 100 (some under 50) as critical. In active major bleeding, replacement is typically given when fibrinogen falls under 150 to 200 mg/dL. High values are not acutely dangerous, though very high levels add slightly to clot risk.

Why is fibrinogen high in pregnancy?

Pregnancy increases production of fibrinogen and several other clotting factors to limit bleeding at delivery. Levels rise from the first trimester and reach 400 to 650 mg/dL at term, returning to normal over about 4 to 6 weeks after birth. Because of this, a level that looks 'normal' (say 250 mg/dL) during heavy bleeding after delivery is actually low for pregnancy and is treated as a warning sign.

How can I lower fibrinogen naturally?

The measures with the best evidence are stopping smoking (levels fall within weeks), losing excess weight (roughly 10 to 30 mg/dL with 5 to 10 percent weight loss) and regular aerobic exercise (similar reductions over 3 to 12 months). A Mediterranean-style diet high in fiber and fish oil supplements have smaller, less consistent effects. Treating the infection or inflammatory disease behind a high value brings it down faster than any lifestyle change.

What is the difference between fibrinogen activity and fibrinogen antigen?

The usual test (Clauss fibrinogen) measures activity, how well your fibrinogen actually clots. The antigen test measures how much fibrinogen protein is present regardless of whether it works. If both are low, you have hypofibrinogenemia or a consumption problem; if activity is low but antigen is normal, the protein is abnormal (dysfibrinogenemia), which can cause bleeding, clotting or neither and is often inherited.

References

Fibrinogen test. MedlinePlus, US National Library of Medicine (2023)View source
Fibrinogen Studies Collaboration; 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)
Charbit B, Mandelbrot L, Samain E, et al.. The decrease of fibrinogen is an early predictor of the severity of postpartum hemorrhage. Journal of Thrombosis and Haemostasis (2007)
Levy JH, Welsby I, Goodnough LT. Fibrinogen as a therapeutic target for bleeding: a review of critical levels and replacement therapy. Transfusion (2014)
Spahn DR, Bouillon B, Cerny V, et al.. The European guideline on management of major bleeding and coagulopathy following trauma: fifth edition. Critical Care (2019)
Taylor FB Jr, Toh CH, Hoots WK, Wada H, Levi M. Towards definition, clinical and laboratory criteria, and a scoring system for disseminated intravascular coagulation. Thrombosis and Haemostasis (2001)
Casini A, de Moerloose P, Neerman-Arbez M. Clinical features and management of congenital fibrinogen deficiencies. Seminars in Thrombosis and Hemostasis (2016)
Kamath S, Lip GY. Fibrinogen: biochemistry, epidemiology and determinants. QJM (2003)
Kannel WB, Wolf PA, Castelli WP, D'Agostino RB. Fibrinogen and risk of cardiovascular disease: the Framingham Study. JAMA (1987)
Ernst E. Regular exercise reduces fibrinogen levels: a review of longitudinal studies. British Journal of Sports Medicine (1993)
Hsia CH, Shen MC, Lin JS, et al.. Nattokinase decreases plasma levels of fibrinogen, factor VII, and factor VIII in human subjects. Nutrition Research (2009)
Disseminated intravascular coagulation (DIC). Merck Manual Professional Version (2024)

Related markers

Related conditions

Evidence guides

Worried about your number?

Ask AskMN what your Fibrinogen result could mean in the context of your other results, symptoms and medications. Free, unlimited, no account needed.

Ask about my Fibrinogen

This page is educational and is not medical advice or a diagnosis. Lab results have to be interpreted together with your history, symptoms and other results by a clinician who knows you. Do not start or stop a supplement to change a lab value before the cause is known.