Tests for fibrinogen

Fibrinogen concentration can be

measured in 3 ways. Fibrinogen concentration is usually reported in

milligrams per deciliter (mg/dl).

1. Heat precipitation: This test is

performed on EDTA samples only and

is used for determination of fibrinogen concentration as an indicator of

inflammation in large animals.

Fibrinogen is an acute phase reactant

protein and elevated values are seen in

inflammation and renal disease (for the

latter, in the cat and cow especially).

This method of fibrinogen determination is not sensitive enough

to detect decreased fibrinogen

concentration in coagulation

abnormalities. The method is as

follows:

Two microhematocrit tubes are filled

with EDTA-anticoagulated blood. One

is centrifuged and the total protein in

the plasma is measured by

refractometer. The second tube is heated at 56 C for 3 minutes, which

precipitates the fibrinogen. The second

tube is then centrifuged and the protein

result read similarly. The protein result

in the heated tube is subtracted from

the result in the unheated tube; the

difference is equivalent to the fibrinogen that was removed from the

plasma in the second tube by heating

and centrifuging.

2. Clotting method - thrombin clot

time: The clotting method is a direct measurement of functional fibrinogen.

This method involves the thrombin

clot time (TCT), which is the time

taken for a standardized thrombin

solution to convert fibrinogen to fibrin

to form a clot. Clot formation is

decreased (which will prolong the

TCT) if there is a deficiency of

(hypofibrinogenemia) or abnormal

(dysfibrinogenemia) fibrinogen. This is the technique used by the Comparative

Coagulation Laboratory at Cornell

University for measurement of

fibrinogen in citrated plasma samples

(and is usually a part of the coagulation

panel). Therefore, the TCT will be

prolonged with:

1.

Inherited and acquired

hypofibrinogenemia or dysfibrinogenemia;

DIC consumption of fibrinogen);

2. H

Heparin therapy (for preventing

thrombosis)

3. S

ynthetic liver failure (resulting in

decreased fibrinogen production).

3.Clotting method - fibrinogen concentration (clottable fibrinogen):

Fibrinogen concentration is determined

using the TCT, where the time taken

for the patient's sample to clot is

compared to a standard curve prepared

from (preferably) species-specific

fibrinogen. The TCT is inversely proportional to the fibrinogen

concentration, therefore a long TCT

indicates a hypofibrinogenemia and

vice versa.

NORMAL VALUS : Horse , sheep and dog 100 – 500

mg/dl

Cow 300 - 700

mg/dl

Plasma protein : Fibrinogen ratio

Normal 15:1 , abnormal 10:1except in

sever hypoproteinemia . Interpretation : Estimation of plasma

fibrinogen have been compaired to

TLC and Neutrophil counts in dog . It

was concluded that fibrinogen

increases indicated the presence of the inflammation

Immunologic assays: Fibrinogen

antigen can be measured in

immunologic assays in which the immunoprecipitate formed after

reaction with specific antifibrinogen

antisera is quantitated.