Final answer:
Serum separator tubes should not be used for Phenobarbital, Theophylline, and Digoxin levels for therapeutic monitoring (D) All of the above. SSTs may absorb or interact with these drugs during processing, which can lead to inaccurate measurements.
Step-by-step explanation:
Serum separator tubes (SST) are commonly used in clinical chemistry to separate the serum from whole blood cells. Serum is the liquid portion of blood obtained after removal of cells and clotting factors, used for various diagnostic purposes including therapeutic drug monitoring (TDM). However, not all therapeutic drugs are suitable for monitoring using SST. Considering the properties of drugs such as Phenobarbital, Theophylline, and Digoxin, and based on the process of TDM, which involves measurement of drug concentrations in plasma or serum, the serum separator tubes should not adversely affect the drug levels being tested.
Therefore, the answer to the question 'Serum separator tubes should not be used for which of the following therapeutic monitoring?' would be (D) All of the above, as each of these drug levels could potentially be affected by the gel barrier in SSTs that may absorb or interact with the drug compounds during the separation process.