Antibodies to SF are precoated onto membrane as a capture reagent on the test zone. During the test, specimen is allowed to react with the colloidal gold particles, which have been labeled with antibodies to SF. If SF is present, a red colored line will develop on the membrane in proportion to the amount of SF present in the specimen. To serve as a procedural control, red colored line in the control zone will always appear regardless of the presence of SF.