Cortisol (U4 Bedtime) Test

This test measures free cortisol at bedtime, when levels should be very low. Cortisol that remains high at night can interfere with sleep onset, deep sleep, and nighttime repair. Common contributors include stress, circadian rhythm disruption, alcohol, and blood sugar instability. Low bedtime cortisol is generally expected, but extremely low levels may contribute to nighttime fatigue or low blood pressure symptoms.