Good morning,
I use . cutpt to calculate cut points (reference ranges) for laboratory diagnostic methods. My outcome (classvar) is continuous (concentration in pg/mL). In one case I am getting very discrepant results of the AUC after . cutpt and . roctab. They are here:

Code:
. cutpt c1 ov

Empirical cutpoint estimation
Method: Liu
Reference variable: c1 (0=neg, 1=pos)
Classification variable: ov
Empirical optimal cutpoint: 571.5
Sensitivity at cutpoint: 0.94
Specificity at cutpoint: 0.78
Area under ROC curve at cutpoint: 0.86
and:

Code:
. roctab c1 ov

                      ROC                    -Asymptotic Normal--
           Obs       Area     Std. Err.      [95% Conf. Interval]
     ------------------------------------------------------------
           133     0.9282       0.0210        0.88708     0.96929
For all other outcomes (five or so) the difference is negligible (say, 0.01).

(1) Is there any explanation for this discrepancy?
(2) What does it actually mean "Area under ROC curve at cutpoint"? To my understanding there is not such thing as AUC at cutpoint; AUC is one and the same for all points.

Thank you in advance for commenting.
Best,
Piotr Lewczuk