Your question implies that you are looking for the validity of the temperature assessment when done based on wrist. The possible way to do this is to record temperature by Gold standard as well as based on wrist. Based on some 20-30 pairs of observations, you can establish the correlation between the Gold standard and the wrist temperature. A regression equation can be developed to apply some suitable corrections to the temperature based on wrist. Thereafter, the wrist temperature can be used for any assessment. 

Thank you for the courtesy of your reply.   I will pursue that with a patient population.

You may find some interest in reading this paper

All best

Wrist temperature and cortisol awakening response in humans with social jetlag in the North. Polugrudov AS1, Panev AS1, Smirnov VV1, Paderin NM1, Borisenkov MF1, Popov SV. Chronobiol Int. 2016;33(7):802-9. 

I did not check it, but the best estimation of basal temperature from the wrist might be measuring IR (thermal radiation) above the Radial Artery. Main conduit arteries might best preserve the basal blood temperature. Of course, isolation from environmental temperature is necessary.

Temperature rhythm is highly correlated with the rest-activity (sleep-wake) rhythm, and is also highly influenced by the environment. In order to use wrist temperature as a circadian marker, you should aim to control the rest-activity (sleep-wake) rhythm and environmental conditions as much as possible.