Pre-test for Sculptra Not Possible?

A true allergy to Sculptra is rare. Lumps and bumps, even if delayed, caused by the immune system and form as granulomas, are not allergies, so skin testing won't show a reaction. Most lumps are felt rather than seen and are a physical consequence of the product. Delayed granulomas can happen, although not very common, I am not aware of any skin or blood test that can give this information in advance. Even if you were to place some Sculptra under the skin of the forearm, or behind the ear, and have a negative test (no indication for a granuloma, waiting even a few years to make sure it doesn't happen), you won't have a guarantee it won't happen on the face.

As stated below, allergic reactions are exceptionally rare with sculptra. However, that does not mean you may not experience an undesireable foreign body reaction.
Sculptra is one of the most expensive fillers available and hence, it is not a popular option. Generally a full vial is opened for each patient. However, a full vial is not used for a skin test. You would need to undergo testing the same day as another individual recieving a treatment. So you must coordinate this with the physician. Generally injectors will charge for this service.

Although allergic reactions have not been reported, it certainly would be easy to do a small skin test before full treatment. The most common complication is, however, palpable but invisible nodules. These can occur months after injection. I am not sure how predictable a skin test would be to prevent this complication.

It used to be the rule that when using collagen, a pre-test was done to determine allergies. On rare occasions, when a patient really wants to do it, I will do a test of another filler like Restylane which is not normally needed.
They do have to buy the entire syringe as it cannot be used on someone else, but the tests have always been negative and they can proceed to use the rest of the syringe with confidence.