If a value of 1.1 mg/dL is used as the cutoff for disease (i.e. >1.1 is a screen positive), what is the specificity of this screening procedure?

The mean level of creatinine in the general population is 0.9 mg/dL and the population standard deviation is 0.2 mg/dL. An investigator predicts that creatinine levels will be elevated in individuals with kidney disease. That is, he wants to test Ho: H = 0.9 mg/dL Ha: M > 0.9 mg/DL