A male client arrives at the mental health clinic and asks the nurse for more lithium and the antidepressant amitriptyline that he uses to help him sleep. After reviewing the assessment findings with the healthcare provider, a serum creatinine is obtained. Which information supports the reason for this laboratory test?

Creatinine can measure how the body is metabolizing the lithium in the liver.

The effects of amitriptyline can promote and potentiate the risk of lithium toxicity.

The combination of lithium and amitriptyline may need to be changed if creatinine is high.

Lithium is excreted by the kidneys, and creatinine is related to kidney functioning.