However, a number of factors may contribute to the need for multiple unnecessary measurements, including timing and location of blood draw, variability in PTH half-life (particularly in patients with renal and/or liver failure), use of certain anesthetics such as propofol, and acute fluctuations in PTH levels secondary to physical manipulation of the adenoma itself, thereby further lengthening operative time [30]. The gene discussed is PTH; the disease is liver failure.