Fibrinogen Determination Methods in Differential Diagnosis

Use of Fibrinogen Determination Methods in Differential Diagnosis of Hypofibrinogenemia and Dysfibrinogenemia

Ingrid Skornova, Tomas Simurda, Jan Stasko, Denis Horvath, Jana Zolkova, Pavol Holly, Monika Brunclikova, Matej Samos, Tomas Bolek, Martin Schnierer, Ludek Slavik and Peter Kubisz

Clinical Laboratory. 2021;67:1028–34. DOI: 10.7754/Clin.Lab.2020.200820

Decreased levels of the coagulation factor fibrinogen are found in a range of disorders that includes the congenital disorders afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia and hypodysfibrinogenemia, and disseminated intravascular coagulation and some severe hepatic conditions. Increased blood loss and fibrinolytic therapy can also cause decreased fibrinogen levels.

This study examined the use of fibrinogen determination methods to differentially diagnose the congenital fibrinogen disorders of hypofibrinogenemia and dysfibrinogenemia. These rare disorders may present as bleeding or unusual thrombotic events, but are commonly asymptomatic and are often diagnosed as an incidental finding (de Moerloose et al., 2013). The two disorders differ in the type and magnitude of fibrinogen reduction (Table 1).

Table 1. Comparison of hypofibrinogenemia and dysfibrinogenemia characteristics

In routine practice, fibrinogen is usually measured by both functional and immunological tests. The most common functional tests are the fibrinogen Clauss assay and the prothrombin time derived fibrinogen assay (PT-derived fibrinogen assay). The Clauss assay is a direct measurement of functional activity. In contrast, the PT-derived assay is an indirect, non-standardised measure of activity; the results of this test can vary with the type of reagents and instrument used. However, the PT-derived assay gives rapid results. Fibrinogen antigen concentration is measured by enzyme-linked immunosorbent assays (ELISA), radial immunodiffusion and electrophoresis (Stang & Mitchell, 2013).

What did the researchers do?

The researchers collected blood for plasma fibrinogen tests from 40 patients with dysfibrinogenemia (30 females, 10 males; median age, 41 years, range 2–74 years), 20 patients with hypofibrinogenemia (10 females, 10 males; median age, 35 years, range 2–69 years), and a control group of 40 donors (15 females, 25 males; median age, 40 years, range 18–60 years). They measured fibrinogen functional levels with both the Clauss assay and the PT-derived assay, and fibrinogen concentration with an immunoturbidimetric assay (LIA).

Pearson’s correlation analysis was used to examine the relationships between two variables. P-values of <0.05 were considered significant. The researchers then used sophisticated statistical analysis (linear and quadratic interpolation functions) of positive, sufficiently large linear correlations. This calculation allowed them to compare the results of the different tests, and to predict the result of the more accurate, but possibly more expensive, Clauss assay from the result of the indirect, non-standardised PT-derived assay.

What did the researchers find?

The correlation between fibrinogen levels measured with the PT-derived fibrinogen assay and the fibrinogen Clauss assay in the patients with hypofibrinogenemia was highly significant (P<0.0001). In contrast, in the patients with dysfibrinogenemia, the median fibrinogen level determined with the PT-derived fibrinogen assay (with the particular reagents and instrument used) was about four times higher than that determined by the fibrinogen Clauss assay (Figure 1). Hence, the PT-derived fibrinogen test overestimates plasma fibrinogen in this group, and may incorrectly indicate normal fibrinogen values.

Figure 1. The linear correlation between results of the PT-derived fibrinogen assay and the fibrinogen Clauss assay in patients with hypofibrinogenemia (A) and dysfibrinogenemia (B). FBG_Clauss_g_L, fibrinogen estimated from Clauss assay (g/L); PT_der_FBG_g_L, fibrinogen estimated from PT-derived assay (g/L).

The statistical calculation performed by the researchers could predict the results of both the fibrinogen Clauss assay and the fibrinogen antigen assay from the results of the PT-derived assay.

What were the main conclusions?

Patients, particularly asymptomatic patients, may be at greater risk of incorrect diagnosis and treatment if the PT-derived fibrinogen assay is used as the sole test to evaluate patients for hypofibrinogenemia. Although the PT-derived assay may be useful as a screening test, both the PT-derived assay and the fibrinogen Clauss assay should be used to determine the level of fibrinogen. Because the Clauss assay is the most accurate assay, it should be used if fibrinogen levels need monitoring (e.g. perioperative management).

The statistical procedure may be useful in basal coagulation screening for rapidly estimating fibrinogen activity and antigen concentration. However, it is not determinative and is insufficient to confirm a diagnosis.

Because congenital fibrinogen disorders are rare, the authors recommend collaborating with other centres to develop a larger study.

For more information on the diagnosis of all forms of fibrinogen deficiency, follow this link.

References

de Moerloose P, Casini A, Neerman-Arbez M. Congenital fibrinogen disorders: an update. Semin Thromb Hemost. 2013;39:585–95.

Stang LJ, Mitchell LG. Fibrinogen. In: Monagle, P (Ed.) Haemostasis. 2013;992:181–92. Available at: https://link.springer.com/protocol/10.1007/978-1-62703-339-8_14 (accessed 29 June 2021).