Total testosterone measures all testosterone in the blood, including both bound (to SHBG and albumin) and unbound (free) fractions. It's the primary diagnostic marker for hypogonadism and the most important number for tracking TRT response. The reference range of 300-1000 ng/dL is broad; most men on optimized TRT target the upper third (700-1000 ng/dL).
Blood should be drawn in the morning (before 10 AM) at trough (just before next injection) for accurate assessment.