What does fibrinogen do?

Fibrinogen is a clotting protein made by the liver. During clotting it is converted into fibrin strands, which hold a clot together and stop bleeding.

What does a high fibrinogen level mean?

A high level can be seen with infection or inflammation, including a recent illness, and on its own does not diagnose anything. A clinician can tell you whether a repeat test or other markers such as hs-CRP are useful.

What does a low fibrinogen level mean?

Low fibrinogen can mean an inherited or acquired deficiency, that fibrinogen is being used up faster than it is made, or heavy bleeding. Because it can affect clotting, a low result should be reviewed promptly with a clinician.

No. There is no fasting or special preparation. Let your clinician know if you take blood thinners.

Why does the tube have to be filled exactly?

The light-blue tube contains a measured amount of citrate that stops the blood from clotting. Too much or too little blood changes the ratio and can distort clotting results, so the phlebotomist fills it to the line and processes it promptly.

How fast will I get results?

Quest typically reports fibrinogen within 1-3 days after the sample reaches the lab. Results appear in your private JustLabs dashboard.

Can I use my FSA or HSA, and does insurance cover it?

JustLabs is a cash-pay service: the test is $18, plus one flat $18 Lab & Physician Order Fee per order, and no insurance claim is filed. Lab tests are generally eligible for FSA and HSA funds, and JustLabs provides an itemized receipt you can submit, but check with your plan administrator to confirm.

Back to Tests

❤️ Heart Health

Fibrinogen Activity Test (Clauss)

Fibrinogen

Measures the activity of fibrinogen, the protein your blood turns into fibrin to form a clot. It is used to look into unexplained bleeding or clotting problems.

Fibrinogen (clotting factor I) is a protein made by the liver. When a blood vessel is injured, the clotting cascade converts fibrinogen into strands of fibrin that knit platelets together into a stable clot. Without enough working fibrinogen, clots form poorly and bleeding can be prolonged.

This test uses the Clauss method, a clotting-based measurement. The result reflects functional fibrinogen, the amount that actually works in clot formation.

Clinicians order fibrinogen mainly when someone has unusual bleeding or clotting, often alongside the prothrombin time (PT/INR) and a CBC with platelet count. Low fibrinogen can come from an inherited or acquired deficiency, from fibrinogen being used up faster than it is made, or from heavy bleeding. Infection and inflammation can also change fibrinogen levels, so results are always read in the context of your health at the time.

The sample needs careful handling: a light-blue citrate tube filled to the correct level, processed promptly. Quest Patient Service Centers collect coagulation samples routinely.

Price

$18

All-in

$36

incl. $18 lab & physician fee

Results

1-3 business days

Fasting

Not Required

What's Measured

Fibrinogen Activity

What This Test Measures

Functional (active) fibrinogen in citrated plasma, measured by the Clauss clotting method and reported as a concentration in mg/dL.

Who Should Consider This Test

People with unexplained or excessive bleeding or bruising, people being evaluated for a clotting problem alongside PT/INR and platelet count, people with a known or suspected inherited fibrinogen disorder, and people whose clinician wants to follow fibrinogen alongside inflammation markers.

Health Insights

Conditions Screened

Fibrinogen deficiency (inherited or acquired)Bleeding disordersDisseminated intravascular coagulation (DIC)Clotting evaluation alongside PT/INR

Related Symptoms

Easy or unexplained bruisingProlonged bleeding after cuts or proceduresHeavy menstrual bleedingFrequent nosebleeds

When to Get Tested

When a clinician wants to evaluate bleeding or clotting, or when a previous result needs to be rechecked. Because infection and inflammation can affect fibrinogen, a result taken during or soon after an acute illness may not reflect your usual level.

No fasting needed. How to prepare for your blood test →

Understanding Your Results

Quest reports fibrinogen activity in mg/dL; Quest's reference range for this test is 175-425 mg/dL. A low result can reflect an inherited fibrinogen deficiency or abnormal fibrinogen, an acquired deficiency, consumption of clotting factors as in disseminated intravascular coagulation (DIC), excessive breakdown of clots, or heavy bleeding. A high result can be seen with infection or inflammation, and is not a diagnosis on its own. Review your results with a clinician, who will interpret them alongside PT/INR, platelet count and your history; a clearly low result should be followed up promptly.

What to Expect

After placing your order, we send it straight to Quest Diagnostics — there is no consent form to sign and no partner email to wait for. Your requisition is usually ready to download from your dashboard within about an hour, and you can book your blood draw at any Quest Diagnostics location.

The blood draw typically takes just a few minutes. Results are usually available within 1-3 business days and will appear in your secure JustLabs dashboard.

Our results include reference ranges and easy-to-understand indicators showing whether your values are within normal limits.

How much does the Fibrinogen test cost?

The Fibrinogen test costs $18 at JustLabs — $36 all-in, since the $18 lab & physician order fee is charged once per order, however many tests you add. The price is fixed before your blood draw; no insurance or doctor visit needed.