Low testosterone can be identified through a simple blood test performed by a laboratory, ordered by a health care provider. Blood for the test must be taken in the morning hours, when levels are highest, as levels can drop by as much as 13% during the day and all normal reference ranges are based on morning levels. However, low testosterone in the absence of any symptoms does not clearly need to be treated.

Normal total testosterone levels depend on the man's age but generally range from 240–950 ng/dL (nanograms per deciliter) or 8.3-32.9 nmol/L (nanomoles per liter). Some men with normal total testosterone have low free or bioavailable testosterone levels which could still account for their symptoms. Men with low serum testosterone levels should have other hormones checked, particularly luteinizing hormone to help determine why their testosterone levels are low and help choose the most appropriate treatment (most notably, testosterone is usually not appropriate for secondary or tertiary forms of male hypogonadism, in which the LH levels are usually reduced).

Treatment is often prescribed for total testosterone levels below 230 ng/dL with symptoms. If the serum total testosterone level is between 230 and 350 ng/dL, free or bioavailable testosterone should be checked as they are frequently low when the total is marginal.

The standard range given is based off widely varying ages and, given that testosterone levels naturally decrease as humans age, age-group specific averages should be taken into consideration when discussing treatment between doctor and patient. In men, testosterone falls approximately 1 to 3 percent each year.

- Blood testing

A position statement by the Endocrine Society expressed dissatisfaction with most assays for total, free, and bioavailable testosterone. In particular, research has questioned the validity of commonly administered assays of free testosterone by radioimmunoassay. The free androgen index, essentially a calculation based on total testosterone and sex hormone-binding globulin levels, has been found to be the worst predictor of free testosterone levels and should not be used. Measurement by equilibrium dialysis or mass spectroscopy is generally required for accurately results, particularly for free testosterone which is present normal in such small concentrations.

The third indicator is the presence of clues to specific disorders of the reproductive system.

- Malnutrition or anorexia nervosa severe enough to delay puberty will give other clues as well.

- Poor growth would suggest the possibility of coeliac disease, hypopituitarism or Turner syndrome.

- Reduced sense of smell (hyposmia) or no sense of smell (anosmia) suggests Kallmann syndrome.

The first is simply degree of lateness: although no recommended age of evaluation cleanly separates pathologic from physiologic delay, a delay of 2–3 years or more warrants evaluation.

- In girls, no breast development by 13 years, or no menarche by 3 years after breast development (or by 16).

- In boys, no testicular enlargement by 14 years, or delay in development for 5 years or more after onset of genitalia enlargement.

A delay of two standard deviations has been proposed as a standard.

Testing serum LH and FSH levels are often used to assess hypogonadism in women, particularly when menopause is believed to be happening. These levels change during a woman's normal menstrual cycle, so the history of having ceased menstruation coupled with high levels aids the diagnosis of being menopausal. Commonly, the post-menopausal woman is not called hypogonadal if she is of typical menopausal age. Contrast with a young woman or teen, who would have hypogonadism rather than menopause. This is because hypogonadism is an abnormality, whereas menopause is a normal change in hormone levels. In any case, the LH and FSH levels will rise in cases of primary hypogonadism or menopause, while they will be low in women with secondary or tertiary hypogonadism.

Hypogonadism is often discovered during evaluation of delayed puberty, but ordinary delay, which eventually results in normal pubertal development, wherein reproductive function is termed constitutional delay. It may be discovered during an infertility evaluation in either men or women.

The diagnosis is often one of exclusion found during the workup of delayed puberty.

A paper published in 2012 by Prof. Jacques Young highlights a typical example of the diagnostic work up involved in a suspected case of KS/CHH.

One of the biggest problems in the diagnosis of KS and other forms of CHH is the ability to distinguish between a normal constitutional delay of puberty and KS or CHH.

The main biochemical parameters in men are low serum testosterone and low levels of the gonadotropins LH and FSH, and in women low serum oestrogen and low levels of LH and FSH.

For both males and females with constitutional delay of puberty, endogenous puberty will eventually commence without treatment. However a delay in treatment in a case of KS/HH will delay the physical development of the patient and can cause severe psychological damage. The "wait and see" approach applied to "late bloomers" is probably counterproductive to the needs of the patient whereas a step-by-step approach with hormone replacement therapy used with slowly increasing doses can be used as a diagnostic tool.

Post natal diagnosis of KS / CHH before the age of 6 months is sometimes possible. The normal post natal hormonal surge of gonadotropins along with testosterone or oestrogen is absent in babies with KS / CHH. This lack of detectable hormones in the blood can be used as a diagnostic indicator, especially in male infants.

Normally testicular enlargement is the key sign for the onset of puberty in boys however the use of nighttime LH sampling can help predict the onset of puberty.

In females diagnosis is sometimes further delayed as other causes of amenorrhoea normally have to be investigated first before a case of KS/CHH is considered. KS/CHH can still occur in females in cases when menstruation has begun but stopped after one or two menstrual bleeds. A study of GnRH deficient women in 2011 showed that 10% had experienced one or two bleeds before the onset of amenorrhoea.

In males, treatment with age-appropriate levels of testosterone can be used to distinguish between a case of KS/CHH from a case of delayed puberty. If just delayed the testosterone can "kick-start" endogenous puberty, as demonstrated by testicular enlargement, whereas in the case of KS/CHH there will be no testicular enlargement while on testosterone therapy alone. If no puberty is apparent, especially no testicular development, then a review by a reproductive endocrinologist may be appropriate. Dr Richard Quinton, a leading UK expert on KS/CHH, suggests that if puberty is not apparent by the age of 16 then the patient should be referred for endocrinological review.

A full endocrine workup will be required to measure the levels of the other pituitary hormones, especially prolactin, to check that the pituitary gland is working correctly. There can be other general health issues such as being overweight or having an underlying chronic or acute illness which could cause a delay of puberty. This makes it essential for a patient to get a full endocrine review to distinguish between a case of KS/CHH and another cause for the pubertal delay.

Bone age can be assessed using hand and wrist X-rays. If the bone age is significantly lower than the chronological age of the patient, this could suggest delayed puberty unless there is another underlying reason for the discrepancy.

A karyotype may be performed to rule out Klinefelter syndrome and Turner syndrome, although the hormones levels would also rule out both these relatively common reasons for hypogonadism.

A magnetic resonance imaging (MRI) scan can be used to determine whether the olfactory bulb is present and to check for any physical irregularities of the pituitary gland or hypothalamus.

A standard smell test can be used to check for anosmia, but it must be remembered that even in total anosmia various substances (such as menthol and alcohol) can still be detected by direct stimulation of the trigeminal nerve.

Genetic screening can be carried out, but in light of the unknown genes involved in the majority of KS and CHH cases, a negative result will not rule out a possible diagnosis.

A review paper published in 2014 highlighted the need for doctors to be aware of the possible diagnosis of KS / HH if pubertal delay is found alongside associated "red flag" symptoms. The symptoms listed in the paper were split into two categories; reproductive symptoms associated with the lack of mini puberty seen between birth and six months of age and non-reproductive symptoms which are associated with specific forms of HH. As with other review papers the authors also warned against the "wait and see" approach when puberty appears to be delayed.

Early puberty is believed to put girls at higher risk of sexual abuse, unrelated to pedophilia because the child has developed secondary sex characteristics; however, a causal relationship is, as yet, inconclusive. Early puberty also puts girls at a higher risk for teasing or bullying, mental health disorders and short stature as adults. Helping children control their weight is suggested to help delay puberty. Early puberty additionally puts girls at a "far greater" risk for breast cancer later in life. Girls as young as 8 are increasingly starting to menstruate, develop breasts and grow pubic and underarm hair; these "biological milestones" typically occurred only at 13 or older in the past. African-American girls are especially prone to early puberty. There are theories debating the trend of early puberty, but the exact causes are not known.

Though boys face fewer problems upon early puberty than girls, early puberty is not always positive for boys; early sexual maturation in boys can be accompanied by increased aggressiveness due to the surge of hormones that affect them. Because they appear older than their peers, pubescent boys may face increased social pressure to conform to adult norms; society may view them as more emotionally advanced, although their cognitive and social development may lag behind their appearance. Studies have shown that early maturing boys are more likely to be sexually active and are more likely to participate in risky behaviours.

Studies indicate that breast development in girls and the appearance of pubic hair in girls and boys are starting earlier than in previous generations. As a result, "early puberty" in children, particularly girls, as young as 9 and 10 is no longer considered abnormal, although it may be upsetting to parents and can be harmful to children who mature physically at a time when they are immature mentally.

No age reliably separates normal from abnormal processes in children, but the following age thresholds for evaluation are thought to minimize the risk of missing a significant medical problem:

- Breast development in boys before appearance of pubic hair or testicular enlargement,

- Pubic hair or genital enlargement (gonadarche) in boys with onset before 9.5 years,

- Pubic hair (pubarche) before 8 or breast development (thelarche) in girls with onset before 7 years,

- Menstruation (menarche) in girls before 10 years.

Medical evaluation is sometimes necessary to recognize the few children with serious conditions from the majority who have entered puberty early but are still medically normal. Early sexual development warrants evaluation because it may:

- induce early bone maturation and reduce eventual adult height,

- indicate the presence of a tumour or other serious problem,

- cause the child, particularly a girl, to become an object of adult sexual interest.

CAIS can only be diagnosed in normal phenotypic females. It is not usually suspected unless the menses fail to develop at puberty, or an inguinal hernia presents during premenarche. As many as 1–2% of prepubertal girls that present with an inguinal hernia will also have CAIS.

A diagnosis of CAIS or Swyer syndrome can be made in utero by comparing a karyotype obtained by amniocentesis with the external genitalia of the fetus during a prenatal ultrasound. Many infants with CAIS do not experience the normal, spontaneous neonatal testosterone surge, a fact which can be diagnostically exploited by obtaining baseline luteinizing hormone and testosterone measurements, followed by a human chorionic gonadotropin (hGC) stimulation test.

The main differentials for CAIS are complete gonadal dysgenesis (Swyer syndrome) and Müllerian agenesis (Mayer-Rokitansky-Kuster-Hauser syndrome or MRKH). Both CAIS and Swyer syndrome are associated with a 46,XY karyotype, whereas MRKH is not; MRKH can thus be ruled out by checking for the presence of a Y chromosome, which can be done either by fluorescence in situ hybridization (FISH) analysis or on full karyotype. Swyer syndrome is distinguished by poor breast development and shorter stature. The diagnosis of CAIS is confirmed when androgen receptor (AR) gene sequencing reveals a mutation, although up to 5% of individuals with CAIS do not have an AR mutation.

Up until the 1990s, a CAIS diagnosis was often hidden from the affected individual and / or family. It is current practice to disclose the genotype at the time of diagnosis, particularly when the affected girl is at least of adolescent age. If the affected individual is a child or infant, it is generally up to the parents, often in conjunction with a psychologist, to decide when to disclose the diagnosis.

Individuals with CAIS are raised as females. They are born phenotypically female and almost always have a heterosexual female gender identity; the incidence of homosexuality in women with CAIS is thought to be less than unaffected women. However, at least two case studies have reported male gender identity in individuals with CAIS.

Gonadectomy at time of diagnosis is the current recommendation for PAIS if presenting with cryptorchidism, due to the high (50%) risk of germ cell malignancy. The risk of malignancy when testes are located intrascrotally is unknown; the current recommendation is to biopsy the testes at puberty, allowing investigation of at least 30 seminiferous tubules, with diagnosis preferably based on OCT3/4 immunohistochemistry, followed by regular examinations. Hormone replacement therapy is required after gonadectomy, and should be modulated over time to replicate the hormone levels naturally present in the body during the various stages of puberty. Artificially induced puberty results in the same, normal development of secondary sexual characteristics, growth spurt, and bone mineral accumulation. Women with PAIS may have a tendency towards bone mineralization deficiency, although this increase is thought to be less than is typically seen in CAIS, and is similarly managed.

Unfortunately, the number of differentials to consider for PAIS is particularly large. Prompt diagnosis is particularly urgent when a child is born with ambiguous genitalia, as some causes are associated with potentially life-threatening adrenal crises. Determination of testosterone, testosterone precursors and dihydrotestosterone (DHT) at baseline and / or after human chorionic gonadotropin (hCG) stimulation can be used to exclude such defects in androgen biosynthesis.

Approximately one half of all 46,XY individuals born with ambiguous genitalia will not receive a definitive diagnosis. Androgen receptor (AR) gene mutations cannot be found in 27% to 72% of individuals with PAIS. As a result, genetic analysis can be used to confirm a diagnosis of PAIS, but it cannot be used to rule out PAIS. Evidence of abnormal androgen binding in a genital skin fibroblast study has long been the gold standard for the diagnosis of PAIS, even when an AR mutation is not present. However, some cases of PAIS, including AR-mutant-positive cases, will show normal androgen binding. A family history consistent with X-linked inheritance is more commonly found in AR-mutant-positive cases than AR-mutant-negative cases.

The use of dynamic endocrine tests is particularly helpful in isolating a diagnosis of PAIS. One such test is the human chorionic gonadotropin (hCG) stimulation test. If the gonads are testes, there will be an increase in the level of serum testosterone in response to the hCG, regardless of testicular descent. The magnitude of the testosterone increase can help differentiate between androgen resistance and gonadal dysgenesis, as does evidence of a uterus on ultrasound examination. Testicular function can also be assessed by measuring serum anti-Müllerian hormone levels, which in turn can further differentiate PAIS from gonadal dysgenesis and bilateral anorchia.

Another useful dynamic test involves measuring the response to exogenous steroids; individuals with AIS show a decreased response in serum sex hormone binding globulin (SHBG) after a short term administration of anabolic steroids. Two studies indicate that measuring the response in SHBG after the administration of stanozolol could help to differentiate individuals with PAIS from those with other causes of ambiguous genitalia, although the response in individuals with predominantly male phenotypes overlaps somewhat with the response in normal males.

Treatment for KS and other forms of HH can be divided into hormone replacement therapy and fertility treatments.

Due to the inability of the streak gonads to produce sex hormones (both estrogens and androgens), most of the secondary sex characteristics do not develop. This is especially true of estrogenic changes such as breast development, widening of the pelvis and hips, and menstrual periods. As the adrenal glands can make limited amounts of androgens and are not affected by this syndrome, most of these persons will develop pubic hair, though it often remains sparse.

Evaluation of delayed puberty usually reveals elevation of gonadotropins, indicating that the pituitary is providing the signal for puberty but the gonads are failing to respond. The next steps of the evaluation usually include checking a karyotype and imaging of the pelvis. The karyotype reveals XY chromosomes and the imaging demonstrates the presence of a uterus but no ovaries (the streak gonads are not usually seen by most imaging). Although an XY karyotype can also indicate a person with complete androgen insensitivity syndrome, the absence of breasts, and the presence of a uterus and pubic hair exclude the possibility. At this point it is usually possible for a physician to make a diagnosis of Swyer syndrome.

Since the Sertoli cells are not affected by Leydig cell hypoplasia, anti-Müllerian hormone is secreted normally and so there are no Müllerian structures. Wolffian structures, such as the prostate, vasa deferentia, and epidydimides are present. In type I, abdominal testes are revealed on ultrasound; in type II testes may be descended or undescended.

People with Leydig cell hypoplasia type I display no response to the hCG stimulation test; there is no increase in serum levels of testosterone and dihydrotestosterone. Leydig cell hypoplasia type II can display either a pronounced rise of testosterone levels or no rise.

In any case, the diagnosis is confirmed on biopsy of the testes, revealing either absent or hypoplastic Leydig cells. The inside of the testis will be grayish and mucous, displaying arrested spermatogenesis and the presence of Sertoli cells. The diagnosis can also be confirmed by looking for mutations in the gene for the LH receptor.

A diagnosis of Leydig cell hypoplasia is usually made in the neonatal period, following the discovery of ambiguous genitalia, or at puberty, when secondary sex characteristics fail to develop. Puberty is the most common time for Leydig cell hypoplasia to be diagnosed.

Patients with Leydig cell hypoplasia may be treated with hormone replacement therapy (i.e., with androgens), which will result in normal sexual development and the resolution of most symptoms. In the case of 46,XY (genetically "male") individuals who are phenotypically female and/or identify as the female gender, estrogens should be given instead. Surgical correction of the genitals in 46,XY males may be required, and, if necessary, an orchidopexy (relocation of the undescended testes to the scrotum) may be performed as well.

Swyer syndrome represents one phenotypic result of a failure of the gonads to develop properly, and hence is part of a class of conditions termed gonadal dysgenesis. There are many forms of gonadal dysgenesis.

Swyer syndrome is an example of a condition in which an externally unambiguous female body carries dysgenetic, atypical, or abnormal gonads. Other examples include complete androgen insensitivity syndrome, partial X chromosome deletions, lipoid congenital adrenal hyperplasia, and Turner syndrome.

Hormone replacement therapy with estrogen may be used to treat symptoms of hypoestrogenism in females with the condition. There are currently no known treatments for the infertility caused by the condition in either sex.

Currently, in the United States and over 40 other countries, every child born is screened for 21-hydroxylaase CAH at birth. This test will detect elevated levels of 17-hydroxy-progesterone (17-OHP). Detecting high levels of 17-OHP enables early detection of CAH. Newborns detected early enough can be placed on medication and live a relatively normal life.

The screening process, however, is characterized by a high false positive rate. In one study, CAH screening had the lowest positive predictive value (111 true-positive cases among 20,647 abnormal screening results in a 2-year period, or 0.53%, compared with 6.36% for biotinidase deficiency, 1.84% for congenital hypo-thyroidism, 0.56% for classic galactosemia, and 2.9% for phenylketonuria). According to this estimate, 200 unaffected newborns required clinical and laboratory follow-up for every true case of CAH.

The consequences to the girl with XX gonadal dysgenesis:

1. Her gonads cannot make estrogen, so her breasts will not develop and her uterus will not grow and menstruate until she is given estrogen. This is often given through the skin now.

2. Her gonads cannot make progesterone, so her menstrual periods will not be predictable until she is given a progestin, still usually as a pill.

3. Her gonads cannot produce eggs so she will not be able to conceive children naturally. A woman with a uterus but no ovaries may be able to become pregnant by implantation of another woman's fertilized egg (embryo transfer).

During pregnancy, the placenta, which is fetal tissue, synthesizes large amounts of estrogen. The levels of estrogen in the mother can elevate 100-fold higher than normal cycling levels. In fetal aromatase deficiency, the placenta synthesizes the intermediates in the biosynthesis of the estrogens, androstenedione and testosterone, but cannot convert them the rest of the way due to the absence of aromatase. These compounds, which are androgens, subsequently accumulate to high levels and circulate, severely masculinizing both the fetus and the mother. The mother will experience cystic acne, hirsutism, deepening of the voice, and clitoromegaly, which will partially reverse following parturition. The fetus, if female, will be born with severely masculinized external genitalia, including labioscrotal fusion and a greatly enlarged phallus. A male fetus will be born with normal genitalia.

At puberty, due to the lack of aromatase, estrogens will not be synthesized by the ovaries, and normal puberty, including breast development and the onset of menses, will not occur. Instead, androgens will elevate once again above normal levels, and may cause additional virilization, such as acne, hirsutism, and further enlargement of the clitoris, unless treatment with estrogen is given.

Aromatase deficiency in the baby can also affect the mother during gestation, with cystic acne, hirsutism, deepening of the voice, and clitoromegaly. Increased circulating testosterone levels are the cause. The mother's symptoms resolve after she gives birth.

In 2013, an 18-year-old woman with EIS was reported. DNA sequencing revealed a homozygous mutation in ESR1, the gene that encodes the ERα. Within the ligand-binding domain, the neutral polar glutamine 375 was changed to a basic, polar histidine. An "in vitro" assay of ERα-dependent gene transcription found that the EC for transactivation had been reduced by 240-fold relative to normal, non-mutated ERα, indicating an extreme reduction in the activity of the receptor. Clinical signs suggested a profile of complete estrogen insensitivity syndrome with a resemblance to ERα knockout mice. The patient presented with delayed puberty, including an absence of breast development (Tanner stage I) and primary amenorrhea, as well as intermittent pelvic pain. Examination revealed markedly enlarged ovaries with multiple hemorrhagic cysts as the cause of the lower abdominal pain.

Estrogen levels were dramatically and persistently elevated (estradiol levels were 2340 pg/mL, regarded as being about 10 times the normal level, and ranged from 750–3500 pg/mL), gonadotropin levels were mildly elevated (follicle-stimulating hormone and luteinizing hormone levels were 6.7–19.1 mIU/mL and 5.8–13.2 mIU/mL, respectively), and testosterone levels were slightly elevated (33–88 ng/dL). Inhibin A levels were also markedly elevated. Sex hormone-binding globulin, corticosteroid-binding globulin, thyroxine-binding globulin, prolactin, and triglycerides, which are known to be elevated by estrogen, were all within normal ranges in spite of the extremely high levels of estrogen, and inhibin B levels were also normal. Her relatively mildly elevated levels of gonadotropins were attributed to retained negative feedback by progesterone as well as by her elevated levels of testosterone and inhibin A, although it was acknowledged that possible effects of estrogen mediated by other receptors such as ERβ could not be excluded.

The patient had a small uterus, with an endometrial stripe that could not be clearly identified. At the age of 15 years, 5 months, her bone age was 11 or 12 years, and at the age of 17 years, 8 months, her bone age was 13.5 years. Her bone mass was lower than expected for her age, and levels of osteocalcin and C-terminal telopeptide were both elevated, suggesting an increased rate of bone turnover. She was 162.6 cm tall, and her growth velocity indicated a lack of estrogen-induced growth spurt at puberty. The patient had normal pubic hair development (Tanner stage IV) and severe facial acne, which could both be attributed to testosterone. Her ovarian pathology was attributed to the elevated levels of gonadotropins. In addition to her absence of breast development and areolar enlargement, the patient also appeared to show minimal widening of the hips and a lack of subcutaneous fat deposition, which is in accordance with the established role of estrogen and ERα in the development of female secondary sexual characteristics.

Treatment of the patient with conjugated equine estrogens and high doses of estradiol had no effect. Although the authors of the paper considered her ERα to be essentially unresponsive to estrogen, they stated that they "[could not] exclude the possibility that some residual estrogen sensitivity could be present in some tissues", which is in accordance with the fact that the EC of her ERα had been reduced 240-fold but had not been abolished. Treatment with a progestin, norethisterone, reduced her estradiol concentrations to normal levels and decreased the size of her ovaries and the number of ovarian cysts, alleviating her hypothalamic-pituitary-gonadal axis hyperactivity and ovarian pathology.

Growth of the penis both before birth and during childhood and puberty is strongly influenced by testosterone and, to a lesser degree, the growth hormone. However, later endogenous hormones mainly have value in the treatment of micropenis caused by hormone deficiencies, such as hypopituitarism or hypogonadism.

Regardless of the cause of micropenis, if it is recognized in infancy, a brief course of testosterone is often prescribed (usually no more than 3 months). This usually induces a small amount of growth, confirming the likelihood of further growth at puberty, but rarely achieves normal size. No additional testosterone is given during childhood, to avoid unwanted virilization and bone maturation. (There is also some evidence that premature administration of testosterone can lead to reduced penis size in the adult.)

Testosterone treatment is resumed in adolescence only for boys with hypogonadism. Penile growth is completed at the end of puberty, similar to the completion of height growth, and provision of extra testosterone to post-pubertal adults produces little or no further growth.

Treatment of HH may consist of administration of either a GnRH agonist or a gonadotropin formulation in the case of primary HH and treatment of the root cause (e.g., a tumor) of the symptoms in the case of secondary HH. Alternatively, hormone replacement therapy with androgens and estrogens in males and females, respectively, may be employed.

Several treatments have been found to be effective in managing AES, including aromatase inhibitors and gonadotropin-releasing hormone analogues in both sexes, androgen replacement therapy with non-aromatizable androgens such as DHT in males, and progestogens (which, by virtue of their antigonadotropic properties at high doses, suppress estrogen levels) in females. In addition, male patients often seek bilateral mastectomy, whereas females may opt for breast reduction if warranted.

Medical treatment of AES is not absolutely necessary, but it is recommended as the condition, if left untreated, may lead to excessively large breasts (which may necessitate surgical reduction), problems with fertility, and an increased risk of endometriosis and estrogen-dependent cancers such as breast and endometrial cancers later in life. At least one case of male breast cancer has been reported.