My son had a partial thyroidectomy done two days ago. how would he find out of the nodule removed was hot or cold?

Review the studies: If memory serves me correctly the designation "hot or cold" represented the appearance on a thyroid nodule on an isotope scan. It was hot if it took up the isotope (was metabolically active) or cold if it didn't (inactive). A review of these studies would provide the answer.

Not important now: During the study phase, knowing if a nodule is hot or cold helps to better characterize possible etiologies of the nodule in search of a diagnosis. A thyroid uptake & scan is noninvasive and used for this purpose. However, after a partial thyroidectomy, the tissue specimen is sent for direct visualization (histopathology) for a final diagnosis obviating the need of a thyroid scan.

Ask surgeon: A hot or cold nodule refers to the nuclear medicine itself. The surgeon send the removed tissue/thyroid to a pathologist who looks for a mass ( adenoma/benign or cancer ) . If your son had a nuclear scan prior to the surgery they ( sugeon or endocrinologist) can correlate the scan to the surgery and answer that for you.

Thyroid scan: If your child had a thyroid scan with iodine 123 prior to surgery and a nodule was detected, the nodule is usually characterized as " hot" (increased uptake) or "cold" (decreased uptake) by the interpretation of the scan. "cold" nodules are more likely to be cancer than "hot" nodules.