Duration of LH and FSH Elevation After Single-Dose Gonadorelin
After a single intravenous dose of gonadorelin, LH levels peak at 30-60 minutes and FSH levels peak at approximately 30 minutes, with both hormones returning toward baseline within 2-4 hours, though FSH may remain modestly elevated for up to 48 hours.
Acute Hormonal Response Pattern
LH Response Kinetics
- Peak LH levels occur 30-60 minutes after intravenous gonadorelin administration 1
- The LH response is rapid and transient, with levels declining back toward baseline within 2-4 hours of the initial peak 1, 2
- In healthy prepubertal girls, the 30-minute LH response ranged from 2.9-9.2 IU/L depending on age, confirming the rapid peak timing 3
FSH Response Kinetics
- FSH peaks at approximately 30 minutes post-injection, similar to LH timing 3
- FSH demonstrates a more prolonged elevation compared to LH, with levels remaining elevated for a longer duration 1, 2
- In studies using human menopausal gonadotropin (which contains FSH), intravenous administration showed FSH returning to baseline within 48 hours, suggesting a similar timeframe for gonadorelin-stimulated FSH 4
Clinical Context and Diagnostic Implications
Single-Dose Testing
- The gonadorelin test is designed as a diagnostic challenge to assess pituitary gonadotroph responsiveness, not as a therapeutic intervention 1
- The test effectively provokes gonadotropin release even in patients with secondary amenorrhea, with peak levels occurring within the first hour 1
- The magnitude of response (delta 1 = peak level minus baseline) is more diagnostically relevant than the absolute duration of elevation 1
Important Caveats
- The response does not immediately depend on basal gonadotropin levels but rather reflects the functional status of the hypothalamic-pituitary axis 1
- In patients with idiopathic hypogonadotropic hypogonadism, a single dose produces a subnormal response, but the timing of peak levels remains consistent at 30-60 minutes 2, 5
- Repeated dosing (not single-dose) can produce sustained elevation: when gonadorelin is administered every 4 hours for one week, basal FSH levels remain elevated throughout the treatment period, but this is not relevant to single-dose kinetics 2
Practical Summary
For clinical interpretation of a gonadorelin stimulation test:
- Draw baseline samples immediately before injection 1, 3
- Obtain peak samples at 30 minutes post-injection for both LH and FSH 1, 3
- Some protocols include a 60-minute sample to capture delayed LH peaks 1
- By 2-4 hours, hormone levels are returning to baseline, making later sampling unnecessary for standard diagnostic purposes 1, 2
- FSH may show residual elevation beyond 4 hours, but this is not clinically significant for diagnostic interpretation 4
The transient nature of the response (measured in hours, not days) distinguishes single-dose gonadorelin testing from therapeutic regimens using LHRH agonists, which cause initial stimulation followed by receptor downregulation over 3-4 weeks 6.