Maximum serum concentration of tabalumab, after the loading dose, assessed over the 14-day dosing interval, stratified by device.PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using noncompartmental analysis (NCA) methods to calculate the geometric mean.

PK population: all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data.

Area under the concentration time curve after the loading dose, assessed over the 14-day dosing interval, stratified by device.PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using NCA methods to calculate the geometric mean.

PK population: all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data.

Maximum serum concentration of tabalumab, after the loading dose, assessed over the 14-day dosing interval , stratified by body weight (low <60 kilograms (kg), medium 60kg- 100kg, high >100kg).PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using NCA methods to calculate the geometric mean.

PK population: all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data. The analyses was conducted on tabalumab exposure parameter from both arms combined per the statistical analysis plan, since the tabalumab exposure was similar following prefilled syringe and auto-injector injections.

Area under the concentration time curve after the loading dose, assessed over the 14-day dosing interval, stratified by body weight (low <60 kilograms (kg), medium 60kg- 100kg, high >100kg). PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using noncompartmental analysis (NCA) methods to calculate the geometric mean.

PK population: all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data. The analyses was conducted on tabalumab exposure parameter from both arms combined per the statistical analysis plan, since the tabalumab exposure was similar following prefilled syringe and auto-injector injections.

Participants reporting incomplete dose administration from the study drug administration log.

Safety population: all randomized patients who received at least 1 dose of study treatment.

Participants with treatment-emergent anti-tabalumab antibodies were participants who had any samples from baseline up to and through Week 12 that was a 4-fold increase (2-dilution increase) in immunogenicity titer over baseline titer, or participants who tested negative at baseline and positive post-baseline (at titer of ≥1:20). Baseline is defined as the last non-missing observation on or prior to the date of the first injection of tabalumab. Percentage of participants with anti-tabalumab antibodies = (number of participants with treatment-emergent anti-tabalumab antibodies / number of participants assessed)*100.

Safety population: all randomized participants who received at least 1 dose of study treatment. Participants with a baseline sample and at least 1 evaluable sample after administration of study drug OR participants with no baseline sample and all evaluable post-baseline samples.

The SQAAQ is a 12-item questionnaire using a 7-point Likert scale (from "Strongly Disagree" as 1 to "Strongly Agree" as 7) that provides assessment of ease of use and confidence with using a prefilled syringe or auto-injector to administer a subcutaneous injection of drug. The 12 items are: A-Easy for me to learn how to use, B-Easy for me to unlock, C- Easy to hold in my hand when I inject my dose, D- Easy to inject my dose, E- Easy to know that my dose is complete, F- Easy to store the device in my refrigerator, G- Easy to remove needle shield/cover, H- Easy to pick up, I- Overall, easy to use, J- The device is stable against my skin during the injection, K- I am confident in my ability to use the device, L- I am confident my dose is complete.

Safety population: all randomized patients who received at least 1 dose of study treatment.

Maximum serum concentration of tabalumab in medium body weight group, after the loading dose via auto-injector, assessed over the 14-day dosing interval, stratified by injection site. PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using noncompartmental analysis (NCA) methods to calculate the geometric mean.

PK population (all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data) in medium body weight group, dosed by auto-injector.

Area under the concentration time curve in medium body weight group after the loading dose via auto-injector, assessed over the 14-day dosing interval, stratified by injection site. PK samples taken during the first dosing interval, days 4, 7, 9, 11, 14, were analyzed using noncompartmental analysis (NCA) methods to calculate the geometric mean.

PK population (all randomized participants who received at least one dose of the study drug and had evaluable tabalumab PK data) in medium body weight group, dosed by auto-injector.