Among the patients have blood clots in veins, how many of them have a normal level of complement 4?
APS will result in Blood Clots in veins; normal level of complement 4 refers to C4 > 10; Should compute the number of different ones
SELECT COUNT(DISTINCT T1.ID) FROM Patient AS T1 INNER JOIN Laboratory AS T2 ON T1.ID = T2.ID WHERE T2.C4 > 10 AND T1.Diagnosis = 'APS'