Due to the strong link between PPID and insulin resistance, testing is recommended for all horses suspected or confirmed to be suffering from PPID. There are two tests commonly used for insulin resistance: the oral sugar test and fasting insulin blood concentration.

The fasting insulin concentration involves giving a horse a single flake of hay at 10 pm the night before testing, with blood being drawn the following morning. Both insulin and glucose blood levels are measured. Hyperinsulinemia suggests insulin resistance, but normal or low fasting insulin does not rule out PPID. This test is easy to perform, but is less sensitive than the oral sugar test. It is best used in cases where risks of laminitis make the oral sugar test potentially unsafe.

The oral sugar test also requires giving the horse only a single flake of hay at 10pm the night before the test. The following morning, karo corn syrup is given orally, and glucose and insulin levels are measured at 60 and 90 minutes after administration. Normal or excessively high insulin levels are diagnostic. However, equivocal test results require retesting at a later date, or performing a different test. A similar test is available outside the US, in areas where corn-syrup products are less readily available, where horses are given a morning meal of chaff with dextrose powder, and blood insulin levels are measured 2 hours later.

Levels of LH/FSH may be suppressed by a raised prolactin level, and are therefore not interpretable unless prolactin is low or normal. In men, the combination of low LH and FSH in combination with a low testosterone confirms LH/FSH deficiency; a high testosterone would indicate a source elsewhere in the body (such as a testosterone-secreting tumor). In women, the diagnosis of LH/FSH deficiency depends on whether the woman has been through the menopause. Before the menopause, abnormal menstrual periods together with low estradiol and LH/FSH levels confirm a pituitary problem; after the menopause (when LH/FSH levels are normally elevated and the ovaries produce less estradiol), inappropriately low LH/FSH alone is sufficient. Stimulation tests with GnRH are possible, but their use is not encouraged.

For TSH, basal measurements are usually sufficient, as well as measurements of thyroxine to ensure that the pituitary is not simply suppressing TSH production in response to hyperthyroidism (an overactive thyroid gland). A stimulation test with thyrotropin-releasing hormone (TRH) is not regarded as useful. Prolactin can be measured by basal level, and is required for the interpretation of LH and FSH results in addition to the confirmation of hypopituitarism or diagnosis of a prolactin-secreting tumor.

The diagnosis of hypopituitarism is made on blood tests. Two types of blood tests are used to confirm the presence of a hormone deficiency: basal levels, where blood samples are taken–usually in the morning–without any form of stimulation, and dynamic tests, where blood tests are taken after the injection of a stimulating substance. Measurement of ACTH and growth hormone usually requires dynamic testing, whereas the other hormones (LH/FSH, prolactin, TSH) can typically be tested with basal levels. There is no adequate direct test for ADH levels, but ADH deficiency can be confirmed indirectly; oxytocin levels are not routinely measured.

Generally, the finding of a combination of a low pituitary hormone together with a low hormone from the effector gland is indicative of hypopituitarism. Occasionally, the pituitary hormone may be normal but the effector gland hormone decreased; in this case, the pituitary is not responding appropriately to effector hormone changes, and the combination of findings is still suggestive of hypopituitarism.

The dexamethasone suppression test involves administering dexamethasone, a synthetic glucocorticoid, to the horse, and measuring its serum cortisol levels before and 19–24 hours after injection. In a normal horse, dexamethasone administration results in negative feedback to the pituitary, resulting in decreased ACTH production from the pars distalis and, therefore, decreased synthesis of cortisol at the level of the adrenal gland. A horse with PPID, which has an overactive pars intermedia not regulated by glucocorticoid levels, does not suppress ACTH production and, therefore, cortisol levels remain high. False negatives can occur in early disease. Additionally, dexamethasone administration may increase the risk of laminitis in horses already prone to the disease. For these reasons, the dexamethasone suppression test is currently not recommended for PPID testing.

Hormonal assay : there may be low level of T4, TSH, Estrogen, Gonadotropin, Cortisol and ACTH depending on the extent of necrosis

MRI of the pituitary and hypothalamus: this helps to exclude tumor or other pathologies.

Screening for hypothyroidism is performed in the newborn period in many countries, generally using TSH. This has led to the early identification of many cases and thus the prevention of developmental delay. It is the most widely used newborn screening test worldwide. While TSH-based screening will identify the most common causes, the addition of T testing is required to pick up the rarer central causes of neonatal hypothyroidism. If T determination is included in the screening done at birth, this will identify cases of congenital hypothyroidism of central origin in 1:16,000 to 1:160,000 children. Considering that these children usually have other pituitary hormone deficiencies, early identification of these cases may prevent complications.

In adults, widespread screening of the general population is a matter of debate. Some organizations (such as the United States Preventive Services Task Force) state that evidence is insufficient to support routine screening, while others (such as the American Thyroid Association) recommend either intermittent testing above a certain age in both sexes or only in women. Targeted screening may be appropriate in a number of situations where hypothyroidism is common: other autoimmune diseases, a strong family history of thyroid disease, those who have received radioiodine or other radiation therapy to the neck, those who have previously undergone thyroid surgery, those with an abnormal thyroid examination, those with psychiatric disorders, people taking amiodarone or lithium, and those with a number of health conditions (such as certain heart and skin conditions). Yearly thyroid function tests are recommended in people with Down syndrome, as they are at higher risk of thyroid disease.

In a study of 1,034 symptomatic adults, Sheehan syndrome was found to be the sixth most frequent etiology of growth hormone deficiency, being responsible for 3.1% of cases (versus 53.9% due to a pituitary tumor).

The characteristic blood test results for this disorder can also be found in other disorders (for example TSH-oma (pituitary adenoma), or other pituitary disorders). The diagnosis may involve identifying a mutation of the thyroid receptor, which is present in approximately 85% of cases.

Yet, since discovery of resistance to thyroid hormones in the absence of thyroid hormone receptor beta mutations, lack of a mutation in a patient does not rule out resistance.

Thyroid hormone resistance syndrome is rare, incidence is variously quoted as 1 in 50,000 or 1 in 40,000 live births. More than 1000 individuals have been identified with thyroid hormone resistance, of which 85% had thyroid hormone beta receptor mutation.

In overt primary hyperthyroidism, TSH levels are low and T and T levels are high. Subclinical hyperthyroidism is a milder form of hyperthyroidism characterized by low or undetectable serum TSH level, but with a normal serum free thyroxine level. Although the evidence for doing so is not definitive, treatment of elderly persons having subclinical hyperthyroidism could reduce the incidence of atrial fibrillation. There is also an increased risk of bone fractures (by 42%) in people with subclinical hyperthyroidism; there is insufficient evidence to say whether treatment with antithyroid medications would reduce that risk.

During pregnancy, the thyroid gland must produce 50% more thyroid hormone to provide enough thyroid hormone for the developing fetus and the expectant mother. In pregnancy, free thyroxine levels may be lower than anticipated due to increased binding to thyroid binding globulin and decreased binding to albumin. They should either be corrected for the stage of pregnancy, or total thyroxine levels should be used instead for diagnosis. TSH values may also be lower than normal (particularly in the first trimester) and the normal range should be adjusted for the stage of pregnancy.

In pregnancy, subclinical hypothyroidism is defined as a TSH between 2.5 and 10 mIU/l with a normal thyroxine level, while those with TSH above 10 mIU/l are considered to be overtly hypothyroid even if the thyroxine level is normal. Antibodies against TPO may be important in making decisions about treatment, and should, therefore, be determined in women with abnormal thyroid function tests.

Determination of TPO antibodies may be considered as part of the assessment of recurrent miscarriage, as subtle thyroid dysfunction can be associated with pregnancy loss, but this recommendation is not universal, and presence of thyroid antibodies may not predict future outcome.

Autoantibodies to the thyroid gland may be detected in various disease states. There are several anti-thyroid antibodies, including anti-thyroglobulin antibodies (TgAb), anti-microsomal/anti-thyroid peroxidase antibodies (TPOAb), and TSH receptor antibodies (TSHRAb).

- Elevated anti-thryoglobulin (TgAb) and anti-thyroid peroxidase antibodies (TPOAb) can be found in patients with Hashimoto's thyroiditis, the most common autoimmune type of hypothyroidism. TPOAb levels have also been found to be elevated in patients who present with subclinical hypothyroidism (where TSH is elevated, but free T4 is normal), and can help predict progression to overt hypothyroidism. The American Association Thyroid Association thus recommends measuring TPOAb levels when evaluating subclinical hypothyroidism or when trying to identify whether nodular thyroid disease is due to autoimmune thyroid disease.

- When the etiology of hyperthyroidism is not clear after initial clinical and biochemical evaluation, measurement of TSH receptor antibodies (TSHRAb) can help make the diagnosis. In Grave's disease, TSHRAb levels are elevated as they are responsible for activating the TSH receptor and causing increased thyroid hormone production.

In those without symptoms who are not pregnant there is little evidence for or against screening.

A doctor will test for prolactin blood levels in women with unexplained milk secretion (galactorrhea) or irregular menses or infertility, and in men with impaired sexual function and milk secretion. If prolactin is high, a doctor will test thyroid function and ask first about other conditions and medications known to raise prolactin secretion. While a plain X-ray of the bones surrounding the pituitary may reveal the presence of a large macro-adenoma, the small micro-adenoma will not be apparent. Magnetic resonance imaging (MRI) is the most sensitive test for detecting pituitary tumours and determining their size. MRI scans may be repeated periodically to assess tumour progression and the effects of therapy. Computed Tomography (CT scan) also gives an image of the pituitary, but it is less sensitive than the MRI.

In addition to assessing the size of the pituitary tumour, doctors also look for damage to surrounding tissues, and perform tests to assess whether production of other pituitary hormones is normal. Depending on the size of the tumour, the doctor may request an eye exam with measurement of visual fields.

The hormone prolactin is downregulated by dopamine and is upregulated by oestrogen. A falsely-high measurement may occur due to the presence of the biologically-inactive macroprolactin in the serum. This can show up as high prolactin in some types of tests, but is asymptomatic.

A medical biopsy refers to the obtaining of a tissue sample for examination under the microscope or other testing, usually to distinguish cancer from noncancerous conditions. Thyroid tissue may be obtained for biopsy by fine needle aspiration (FNA) or by surgery.

Fine needle aspiration has the advantage of being a brief, safe, outpatient procedure that is safer and less expensive than surgery and does not leave a visible scar. Needle biopsies became widely used in the 1980s, but it was recognized that the accuracy of identification of cancer was good, but not perfect. The accuracy of the diagnosis depends on obtaining tissue from all of the suspicious areas of an abnormal thyroid gland. The reliability of fine needle aspiration is increased when sampling can be guided by ultrasound, and over the last 15 years, this has become the preferred method for thyroid biopsy in North America.

Diagnosis is by measurement of calcium, serum albumin (for correction) and PTH in blood.

If necessary, measuring cAMP (cyclic AMP) in the urine after an intravenous dose of PTH can help in the distinction between hypoparathyroidism and other causes.

Differential diagnoses are:

- Pseudohypoparathyroidism (normal PTH levels but tissue insensitivity to the hormone, associated with mental retardation and skeletal deformities) and pseudopseudohypoparathyroidism.

- Vitamin D deficiency or hereditary insensitivity to this vitamin (X-linked dominant).

- Malabsorption

- Kidney disease

- Medication: steroids, diuretics, some antiepileptics.

Other tests include ECG for abnormal heart rhythms, and measurement of blood magnesium levels.

Medications to treat hypothyroidism have been found to be safe during pregnancy. Levothyroxine is the treatment of choice for hypothyroidism in pregnancy. Thyroid function should be normalised prior to conception in women with pre-existing thyroid disease. Once pregnancy is confirmed the thyroxine dose should be increased by about 30-50% and subsequent titrations should be guided by thyroid function tests (FT4 and TSH) that should be monitored 4-6 weekly until euthyroidism is achieved. It is recommended that TSH levels are maintained below 2.5 mU/l in the first trimester of pregnancy and below 3 mU/l in later pregnancy. The recommended maintenance dose of thyroxine in pregnancy is about 2.0-2.4 µg/kg daily. Thyroxine requirements may increase in late gestation and return to pre-pregnancy levels in the majority of women on delivery. Pregnant patients with subclinical hypothyroidism (normal FT4 and elevated TSH) should be treated as well, since supplementation with levothyroxine in such cases results in significantly higher delivery rate, with a pooled relative chance of 2.76.

Guidelines for diagnosing hypoprolactinemia are defined as prolactin levels below 3 µg/L in women, and 5 µg/L in men.

Treatment is usually medication with dopamine agonists such as cabergoline, bromocriptine (often preferred when pregnancy is possible), and less frequently lisuride. A new drug in use is norprolac with the active ingredient quinagolide. Terguride is also used.

"Vitex agnus-castus" extract can be tried in cases of mild hyperprolactinaemia.

There are no treatments which increase prolactin levels in humans. Treatment differs based on the reason for diagnosis. Women who are diagnosed with hypoprolactinemia following lactation failure are typically advised to formula feed, although treatment with metoclopramide has been shown to increase milk supply in clinical studies. For subfertility, treatment may include clomiphene citrate or gonadotropins.

A complete physical evaluation should be done prior to initiating more extensive studies, the examiner should differentiate between widespread body hair increase and male pattern virilization. One method of evaluating hirsutism is the Ferriman-Gallwey Score which gives a score based on the amount and location of hair growth on a woman. After the physical examination, laboratory studies and imaging studies can be done to rule out further causes.

Diagnosis of patients with even mild hirsutism should include assessment of ovulation and ovarian ultrasound, due to the high prevalence of polycystic ovary syndrome (PCOS), as well as 17α-hydroxyprogesterone (because of the possibility of finding nonclassic 21-hydroxylase deficiency). Many women present with an elevated serum dehydroepiandrosterone sulfate (DHEA-S) level. Levels greater than 700 μg/dL are indicative of adrenal gland dysfunction, particularly congenital adrenal hyperplasia due to 21-hydroxylase deficiency. However, PCOS and idiopathic hirsutism make up 90% of cases.

Other blood value that may be evaluated in the workup of hirsutism include:

- androgens; androstenedione, testosterone

- thyroid function panel; thyroid-stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4)

- prolactin

If no underlying cause can be identified, the condition is considered idiopathic.

Severe hypocalcaemia, a potentially life-threatening condition, is treated as soon as possible with intravenous calcium (e.g. as calcium gluconate). Generally, a central venous catheter is recommended, as the calcium can irritate peripheral veins and cause phlebitis. In the event of a life-threatening attack of low calcium levels or tetany (prolonged muscle contractions), calcium is administered by intravenous (IV) infusion. Precautions are taken to prevent seizures or larynx spasms. The heart is monitored for abnormal rhythms until the person is stable. When the life-threatening attack has been controlled, treatment continues with medicine taken by mouth as often as four times a day.

Long-term treatment of hypoparathyroidism is with vitamin D analogs and calcium supplementation, but may be ineffective in some due to potential renal damage. The N-terminal fragment of parathyroid hormone (PTH 1-34) has full biological activity. The use of pump delivery of synthetic PTH 1-34 provides the closest approach to physiologic PTH replacement therapy. Injections of recombinant human parathyroid hormone are available as treatment in those with low blood calcium levels.

Hypothalamic disease is a disorder presenting primarily in the hypothalamus, which may be caused by damage resulting from malnutrition, including anorexia and bulimia eating disorders, genetic disorders, radiation, surgery, head trauma, lesion, tumour or other physical injury to the hypothalamus. The hypothalamus is the control center for several endocrine functions. Endocrine systems controlled by the hypothalamus are regulated by anti-diuretic hormone (ADH), corticotropin-releasing hormone, gonadotropin-releasing hormone, growth hormone-releasing hormone, oxytocin, all of which are secreted by the hypothalamus. Damage to the hypothalamus may impact any of these hormones and the related endocrine systems. Many of these hypothalamic hormones act on the pituitary gland. Hypothalamic disease therefore affects the functioning of the pituitary and the target organs controlled by the pituitary, including the adrenal glands, ovaries and testes, and the thyroid gland.

Numerous dysfunctions manifest as a result of hypothalamic disease. Damage to the hypothalamus may cause disruptions in body temperature regulation, growth, weight, sodium and water balance, milk production, emotions, and sleep cycles. Hypopituitarism, neurogenic diabetes insipidus, tertiary hypothyroidism, and developmental disorders are examples of precipitating conditions caused by hypothalamic disease.

Other causes of irregular or absent menstruation and hirsutism, such as hypothyroidism, congenital adrenal hyperplasia (21-hydroxylase deficiency), Cushing's syndrome, hyperprolactinemia, androgen secreting neoplasms, and other pituitary or adrenal disorders, should be investigated.

Some other blood tests are suggestive but not diagnostic. The ratio of LH (Luteinizing hormone) to FSH (Follicle-stimulating hormone), when measured in international units, is elevated in women with PCOS. Common cut-offs to designate abnormally high LH/FSH ratios are 2:1 or 3:1 as tested on Day 3 of the menstrual cycle. The pattern is not very sensitive; a ratio of 2:1 or higher was present in less than 50% of women with PCOS in one study. There are often low levels of sex hormone-binding globulin, in particular among obese or overweight women.

Anti-Müllerian hormone (AMH) is increased in PCOS, and may become part of its diagnostic criteria.