TPO can refer to different things depending on the context:

1. Thyroid Peroxidase (TPO): This is an enzyme primarily found in the thyroid gland. It plays a crucial role in the production of thyroid hormones by catalyzing the oxidation of iodide ions to iodine, which is then added to thyroglobulin to produce thyroid hormones T4 (thyroxine) and T3 (triiodothyronine). The TPO enzyme is important for normal thyroid function and metabolism regulation.
2. Thermoplastic Polyolefin (TPO): This is a type of plastic material made by blending polypropylene or polyethylene with ethylene-propylene rubber (EPR). TPO is known for its durability, flexibility, weather resistance, and chemical stability. It is widely used in automotive parts, roofing membranes, and construction materials. TPO roofing, for example, is a heat-reflective and energy-efficient single-ply membrane used in commercial roofing.
3. TPO gene: The gene responsible for making the thyroid peroxidase enzyme. Mutations in the TPO gene can lead to thyroid disorders like congenital hypothyroidism.
4. TPO antibodies: These are antibodies against thyroid peroxidase, often present in autoimmune thyroid diseases such as Hashimoto's thyroiditis and Graves' disease.

The most common references are either the enzyme related to thyroid function or the plastic material used in manufacturing and construction. If you specify the context, I can provide more detailed information. Let me know if you want details on one of these specifically!