When choosing a protein supplement testing lab, it's important to consider the following factors:

1. Accreditation: Look for a lab that is accredited by organizations such as the International Organization for Standardization (ISO) or the College of American Pathologists (CAP). These accreditations ensure that the lab meets certain quality standards and has the necessary equipment and expertise to perform accurate testing.

2. Experience: Choose a lab that has experience in testing protein supplements specifically, as they will have a deeper understanding of the specific analytical techniques and regulations that are relevant to these products.

3. Testing methods: Make sure the lab uses validated and recognized testing methods, such as HPLC or MS, to ensure accurate and reliable results.

4. Turnaround time: Consider the lab's turnaround time for results, as you may need to receive the results quickly to meet production or regulatory deadlines.

5. Communication and customer service: Look for a lab that provides clear and timely communication throughout the testing process, as well as responsive customer service.

6. Additional services: Some labs may offer additional services such as stability testing, shelf-life testing, and micro-organism testing. Consider if these services are necessary for your product and if the lab can provide them.

7. Cost: Compare the cost of testing from different labs, but keep in mind that the cheapest option may not always be the best choice.

By considering these factors, you can find a protein supplement testing lab that meets your needs and can provide accurate and reliable results.

It is also important to note that some countries may have specific regulations regarding the testing of protein supplements, so it's important to choose a lab that is familiar with these regulations and can help you comply with them.