What is the highest anti-nucleus antibody concentration level of a patient with a normal creatinine level?
highest anti-nucleus antibody concentration level refers to MAX(ANA); normal creatinine level refers to CRE < 1.5;
SELECT T2.ANA FROM Patient AS T1 INNER JOIN Examination AS T2 ON T1.ID = T2.ID INNER JOIN Laboratory AS T3 ON T1.ID = T3.ID WHERE T3.CRE < 1.5 ORDER BY T2.ANA DESC LIMIT 1