A 21 y/o female patient reports to your clinic with absence of menstruation for the past 4 months. The patient is a marathon runner with a BMI of 14 (WHO defines "normal" as 18.5 - 25 kg/m/m) and a body fat of 13% (AJCN defines "normal" as 21% to 32%). The patient has not been sexually active for the past year. Low body fat percentages have been associated with endocrine dysfunction. Which of the following blood test results would explain this patient's symptoms?
a. High GnRH
b. High LH
c. High insulin
d. Low GnRH