Low Testosterone
Low testosterone -- confirmed biochemical deficiency, not just a number on one lab draw -- is evaluated per the Endocrine Society Clinical Practice Guideline (2018). Permanent hypogonadism affects under 1% of men; obesity-related low testosterone affects 2-8%.
Symptoms
Decreased libido, erectile dysfunction, and reduced spontaneous erections are the specific symptoms; fatigue, low mood, and reduced muscle mass are real but nonspecific, and shouldn't drive testing on their own.
Causes and risk
Obesity is the most common reversible driver; aging, chronic illness, and primary testicular or pituitary conditions are the non-reversible causes.
How it is evaluated
Fasting total testosterone drawn 7-10 AM, confirmed on a second morning sample, with the Endocrine Society's 264 ng/dL lower limit as the diagnostic threshold. Free testosterone is added when SHBG is likely altered (obesity, aging).
Treatment
Weight loss is first-line when obesity is the driver. Testosterone therapy is used for confirmed, symptomatic, permanent deficiency, with hematocrit and PSA monitored regularly given the guideline's contraindication list (untreated prostate cancer, severe untreated sleep apnea, uncontrolled heart failure).
When to seek care
Sudden severe testicular pain (possible torsion), new pituitary-mass symptoms (headache, vision changes), or cardiovascular/blood clot symptoms need prompt evaluation.