Calculating sensitivity SS and specificity SP from the SS&SP of subitems

#1
Hello everyone, so here is a question for you.

I have a table of 60 test items that were evaluated in both controls and patients, each item has % correct for the controls, and vs. patients: sensitivity, specificity, ji.

I chose 20 out of these 60 items, and would like now to calculate the sensitivity and specificity (and if possible + and - predictive value) of the 20-item set (ie, if each correct item gives 1 point, out of 20 instead of out of 60) based on the info of this table. Is there anyway I can proceed to do this, even if it is an approximation?

Thnks