In patients with established SIHD, a change in a periodically obtained ECG can be the only evidence of intercurrent silent infarction, inadequately treated hyper- tension, or complex arrhythmia that would modify treat- ment. The timing between routine recordings of the 12- lead ECG that would be required and adequate to accomplish these purposes has not been established, but a consensus recommendation based on expert opinion and common practice would be not greater than once yearly for stable patients with SIHD, as well as at the time of any clinical change. 6.2.5. Focused Follow-Up Visit: Laboratory Examination Patients not known to have diabetes mellitus should have a fasting blood glucose measurement every 3 years to detect new-onset diabetes mellitus, and those with established dia- betes mellitus should have glycosylated hemoglobin mea- sured at least annually to assess glycemic control. A lipid profile should be obtained as clinically warranted. Long-term studies (up to 7 years) demonstrate sustained benefit from continued therapy.18,318 Measurement of creatinine kinase also could be appropriate at these times. In circumstances in which the patient is not concurrently followed up by a primary care physician, measurements of hemoglobin, thy- roid function, serum electrolytes, and renal function should be obtained annually, or sooner when prompted by a change in symptoms or signs. 6.3. Noninvasive Testing in Known SIHD For any patients with known SIHD who have recurrent but stable symptoms after having been symptom free for a period of time on GDMT or after revascularization and who do not fall into any of the categories listed in the previous paragraph, the concepts underlying the recommendations for Noninva- sive Testing for Diagnosis of IHD from Section 2.2 gener- ally apply, with the modifications and special consideration discussed below. 6.3.1. 