Two things have to be true. You have symptoms of testosterone deficiency (low libido, erectile changes, fatigue, loss of muscle or strength, low mood, loss of body hair) and your total testosterone is unequivocally low on two separate blood tests drawn fasting in the morning, when levels peak. The Endocrine Society guideline is explicit that both are required. One afternoon test, or a level in the low-normal range with symptoms that could be sleep, weight, thyroid or depression, is not a diagnosis. A clinic that offers to start you after a single draw, or from a symptom questionnaire, is selling a subscription. Testosterone is also not approved for low levels caused by aging alone, and the guideline advises against routinely treating every older man with a low number.