We know that low levels of factor VIII activity constitutes hemophilia A, but are there any clinical manifestations of elevated factor VIII levels? How can a researcher measure elevated FVIII levels?

There is evidence that a high level of factor VIII is a risk factor for venous thrombosis. There are two articles in Thrombosis and Haemostasis 2000; volume 83:

1.Kraaijenhagen et al. High plasma concentration of factor VIII:c is a major risk factor for venous thromboembolism (p. 5-9)
2.O’Donnell et al. Elevation of FVIII:c in venous thromboembolism is persistent and independent of the acute phase response (p. 10-13)
Both of these recent articles discuss the issue of elevated factor VIII levels as a risk factor for venous thrombosis.

An adaptation of Chromogenix Coamatic® FVIII has been developed to allow accurate determination of elevated factor VIII levels. The method is for research use only.