| Primary Hypogonadism (Testicular Failure) | 
Delayed puberty or incomplete developmentDecreased libidoInfertilityGynecomastiaSmall or underdeveloped testes | 
Serum Testosterone Levels: Low levels.LH and FSH Levels: Elevated (indicating a primary cause).Karyotype Analysis: To detect chromosomal abnormalities like Klinefelter syndrome. | 
Testosterone Replacement Therapy (TRT): To restore normal testosterone levels.Fertility Treatment: Assisted reproductive techniques if fertility is desired.Monitoring and Management: Regular monitoring of testosterone levels, hematocrit, and PSA in men. | 
 | Secondary Hypogonadism (Hypothalamic or Pituitary Dysfunction) | 
Decreased libidoFatigueMuscle weaknessInfertilityPossible headaches and visual disturbances (if a pituitary tumour is present) | 
Serum Testosterone Levels: Low levels.LH and FSH Levels: Low or inappropriately normal.MRI of the Brain: To identify pituitary or hypothalamic lesions.Serum Prolactin Levels: To assess for hyperprolactinemia. | 
Testosterone Replacement Therapy (TRT): To restore normal testosterone levels.Management of Underlying Cause: Surgery, radiation, or medication for pituitary tumours.GnRH Therapy: For hypothalamic causes to stimulate gonadotropin release. | 
 | Congenital Causes (e.g., Klinefelter Syndrome, Kallmann Syndrome) | 
Delayed or absent pubertyGynecomastiaSmall testes (in Klinefelter syndrome)Anosmia (loss of smell in Kallmann syndrome)Infertility | 
Karyotype Analysis: To identify chromosomal abnormalities like 47,XXY in Klinefelter syndrome.Serum Testosterone, LH, FSH Levels: Low testosterone with elevated LH and FSH in Klinefelter syndrome; low levels in Kallmann syndrome.Olfactory Testing: In Kallmann syndrome to confirm anosmia. | 
Testosterone Replacement Therapy (TRT): For development and maintenance of secondary sexual characteristics.Fertility Treatment: Assisted reproductive technologies may be needed for fertility.Psychosocial Support: Counseling for psychological and social impacts of the condition. | 
 | Acquired Causes (e.g., Trauma, Infection, Chemotherapy/Radiation) | 
Sudden onset of hypogonadal symptoms following trauma or treatmentTesticular atrophyInfertilityFatigue and decreased muscle mass | 
Serum Testosterone Levels: Low levels.LH and FSH Levels: Elevated in primary causes; low/normal in secondary causes.Scrotal Ultrasound: To assess testicular damage. | 
Testosterone Replacement Therapy (TRT): To restore normal testosterone levels.Management of Underlying Cause: Treatment or cessation of causative factors (e.g., switching chaemotherapy agents if possible).Fertility Treatment: Consideration of sperm banking before treatment that may cause infertility. | 
 | Age-Related Hypogonadism (Andropause) | 
Gradual decrease in libidoFatigue and decreased energy levelsReduced muscle mass and strengthMood changes, irritability | 
Serum Testosterone Levels: Decreased levels typically associated with aging.LH and FSH Levels: May be normal or slightly elevated.Bone Density Test: To assess for osteoporosis, which may accompany hypogonadism. | 
Testosterone Replacement Therapy (TRT): May be considered based on symptoms and risks.Lifestyle Modifications: Diet, exercise, and weight management to improve overall health.Monitoring: Regular assessment of testosterone levels, hematocrit, and prostate health in men on TRT. |