What is the best way to check a patient's fibrinogen level, particularly in those with a history of bleeding or clotting disorders, undergoing surgery, or with conditions like liver disease or severe trauma?

How to Check Fibrinogen Levels

The Clauss fibrinogen assay is the method of choice for measuring fibrinogen levels in patients with bleeding or clotting disorders, undergoing surgery, or with conditions like liver disease or severe trauma. 1, 2, 3

Primary Testing Method

• Use the Clauss fibrinogen assay as your standard laboratory technique for measuring functional fibrinogen concentration in all clinical scenarios requiring fibrinogen assessment 4, 5, 2
• The Clauss method measures functional fibrinogen activity and correlates with actual hemostatic capacity, making it superior for clinical decision-making compared to other methods 3
• This assay correlates with functional coagulation parameters (Reptilase Time, Thrombin Time, Prothrombin Time) and reflects true hemostatic function 3

Critical Timing Considerations

• Measure fibrinogen early and repeatedly in patients with major bleeding, as fibrinogen depletes first during massive blood loss—reaching critical levels before any other coagulation factor 6, 7, 8
• Fibrinogen concentration is the only coagulation parameter independently associated with progression toward severe bleeding 6
• In trauma patients with significant bleeding, routine practice should include early, repeated measurement of fibrinogen alongside PT, aPTT, and platelets 6

Alternative and Adjunctive Methods

Viscoelastic Testing (Preferred in Emergency Settings)

• Consider viscoelastic methods (ROTEM or TEG) for real-time functional assessment in critical care and trauma settings, as these provide 30-60 minute time savings over conventional laboratory testing 4, 6
• Maximum Clot Firmness (MCF) of 7 mm on viscoelastic testing correlates with fibrinogen levels of approximately 2.0 g/L 6
• Viscoelastic methods avoid the pitfall of overestimation caused by artificial colloids and provide functional assessment of clot formation rather than protein concentration alone 6

Methods to Avoid or Use with Extreme Caution

• Do not rely on PT-derived fibrinogen assays for clinical decision-making in bleeding patients or those with suspected fibrinogen disorders 2, 9, 3
• PT-derived methods overestimate fibrinogen by approximately 4-5 times the actual functional level in patients with dysfibrinogenemia, potentially reporting falsely normal values when fibrinogen is critically low 9, 3
• Results from PT-derived methods are not interchangeable between different methods and can overestimate fibrinogen in certain clinical scenarios 2

Clinical Thresholds for Interpretation

General Populations

• Normal fibrinogen range: 2.0-4.0 g/L (200-400 mg/dL) 4, 5
• Critical threshold requiring intervention: <1.5-2.0 g/L in bleeding scenarios 6, 5, 7
• Levels <1.0 g/L are critically low and indicate immediate need for replacement therapy 6, 5

Trauma Patients

• Maintain fibrinogen >2.0 g/L (200 mg/dL) for effective hemostasis in trauma patients without liver disease 1, 5
• Fibrinogen <2.0 g/L has a 100% positive predictive value for severe hemorrhage in patients with significant bleeding 6
• Target levels ≥1.5-2.0 g/L in coagulopathic trauma patients 7, 8

Cirrhosis Patients

• Fibrinogen <1.0 g/L (100 mg/dL) is associated with spontaneous and procedure-related bleeding in cirrhotic patients 1, 5
• The most agreed upon threshold for fibrinogen replacement in actively bleeding cirrhotic patients is >120 mg/dL (1.2 g/L) 1, 5

Common Pitfalls to Avoid

Artificial Colloid Interference

• Be aware that hydroxyethyl starch causes significant overestimation of fibrinogen concentration when using the Clauss method 4, 6, 5
• Viscoelastic methods avoid this pitfall by measuring functional clot formation rather than protein concentration 6

Delayed Recognition

• Conventional coagulation screens (INR, aPTT) only monitor the initiation phase of coagulation and may appear normal while fibrinogen is critically depleted 6
• Do not rely on PT/INR alone—specific fibrinogen measurement or viscoelastic testing is essential 6

Dysfibrinogenemia Diagnosis

• When dysfibrinogenemia is suspected (low Clauss fibrinogen with normal/high PT-derived fibrinogen), confirm with fibrinogen antigen assays and genetic testing 2, 9
• Fibrinogen antigen assays should be used to distinguish between qualitative (dysfibrinogenemia) and quantitative (hypofibrinogenemia) fibrinogen disorders 2, 9

Special Population Considerations

Pregnancy

• Fibrinogen levels physiologically increase during pregnancy, reaching 3.7-6.2 g/L during the third trimester 4
• In pregnant women with congenital fibrinogen disorders, target trough levels ≥1.0 g/L throughout pregnancy, increasing to ≥1.5 g/L with vaginal bleeding 4

Hemorrhagic Stroke

• Early measurement is essential as fibrinogen depletes first during hemorrhagic emergencies 6
• Maintain levels above 1.5-2.0 g/L in patients with significant bleeding 6