The doctors say no, but is it true?
A toxin test can measure 1-5 picograms of Botulinum toxin type A per milliliter of serum blood.
The specific activity in BOTOX is approx. 20 units / nanogram neurotoxin protein complex. – Page 22 of this document item 11: https://www.allergan.com/assets/pdf/botox_pi
Then a calculation:
20 units = 1 nanogram. Divided 1 by 20, 1 unit = 0.05 nanograms.
Converting nanograms to picograms: 0.05 nanograms = 50 picograms
1 Unit Botox = 50 picograms
1 100 unit injection must therefore contain 5,000 picograms of toxin.
This means that an injection of 100 units of botox (5,000 picograms) should be measurable in 5000 m / L blood, as the test can measure 1-5 picograms per milliliter of blood.