Final answer:
A blood sample is often used for drug testing as it is difficult to tamper with. It provides reliable data because of complex preparation protocols and validated analytical techniques that ensure precision and accuracy.
Step-by-step explanation:
The type of sample often collected for drug testing that is difficult to tamper with or alter is a blood sample. Blood tests are utilized in both clinical therapeutic drug monitoring and pharmacokinetic studies because they are harder to adulterate compared to other types of samples like urine. Blood samples are processed to obtain plasma, which is then quenched with methanol prior to analysis. This procedure helps in reducing the effect of endogenous and exogenous compounds and enhances the method's sensitivity, making it a reliable medium for the detection of drugs.
Moreover, due to the complexity and the need for validated analytical techniques, blood sample preparation protocols are generally more demanding, which further discourages tampering. For instance, when blood samples are collected into tubes containing K2EDTA and then centrifuged, the precision and accuracy of the resulting data are high. These analytical techniques are essential in order to yield exact drug and metabolite quantifications from biological samples, which is imperative in drug testing scenarios.