Why must a discard tube should be collected first before an anticoagulated tube when using a “butterfly” to collect blood?

You are tasked with measuring the quantity of prostate specific antigen (PSA) in a urine sample using an ELISA strategy. Describe and schematically depict how you would perform the test given the following materials: anti-PSA, biotinylated anti-PSA, streptavidin-HRP, HRP substrate kit (HRP = horse radish peroxidase).

Please help a bit confused

Write a lab report on enumeration of lytic viruses : the plaque assay including the sections: introduction, Materials and Methods, Results and Discussion, and citing peer reviewed sources use this data for results section   Group Number Number of Plaques Dilution Factor of Plate Original Concentration of Phage   1 58 10^3 5.80E+04   2 37 10^3 3.70E+04   3 44 10^3 4.40E+04   4 63 10^3 6.30E+04   5 36 10^2 3.60E+03   6 65 10^3 6.50E+04   7 260 10^2 2.60E+04   8 39 10^3 3.90E+04   9 178 10^2 1.78E+04   10 192 10^2 1.92E+04   11 274 10^2 2.74E+04   12 224 10^2 2.24E+04   Class Average 3.52E+04