Diagnosis usually occurs upon investigation of a cause for already suspected Cushing's syndrome. High levels of cortisol observed in patients with PPNAD are not suppressed upon administration of dexamethasone (dexamethasone suppression test), and upon MRI or CT imaging, the pituitary will show no abnormalities. Measuring ACTH will confirm that the cause of the patients Cushing's syndrome is ACTH independent. The nature of Cushing's syndrome itself is periodic, which can make diagnosing PPNAD increasingly difficult.

Diagnosis of PPNAD can be difficult to determine preoperatively as CT scan findings can be variable ie appear normal or suggest unilateral adrenal lesions therefore impeding the correct diagnosis. NP-59 scintigraphy may be particularly useful in identifying the bilateral nature of the disease.

Gene studies are not necessary for diagnosis as there are clear gross and histological diagnostic markers, as the nodules can usually be seen clearly in both cases A positive family history of PPNAD has been shown to be associated with abnormal histological findings, e.g. mitotic figures, which may further hinder diagnosis. At the point where abdominal CT scanning and pituitary fossa MRI show no clear abnormalities, adrenalectomy may be performed.

Acanthosis nigricans is typically diagnosed clinically. A skin biopsy may be needed in unusual cases. If no clear cause is obvious, it may be necessary to search for one. Blood tests, an endoscopy, or X-rays may be required to eliminate the possibility of diabetes or cancer as the cause.

On biopsy, hyperkeratosis, epidermal folding, leukocyte infltration, and melanocyte proliferation may be seen.

Acanthosis nigricans should be distinguished from the casal collar appearing in pellagra.

Common diagnostic techniques include:

- MRIs

- CAT scans

- blood samples.

Blood samples are assessed for the absence or presence of aldosterone and cortisol. Physical examinations are also useful in patients in order to examine vision, skin pigmentation, how the body replaces steroids, and the cranial nerves. Recent advancements in high-resolution MRIs allow for adenomas to be detected during the early stages of Nelson syndrome. Physical examination including height, weight, vital signs, blood pressure, eye examination, thyroid examination, abdominal examination, neurological examination, skin examination and pubertal staging needs to be assessed. Through blood pressure and pulse readings can indicate hypothyroidism and adrenal insufficiency. Hyper-pigmentation, hyporeflexia, and loss of vision can also indicate Nelson's syndrome when assessed together. Specifically for a child who might have Nelson's syndrome, the patient should be questioned about the symptoms of the disease, and well as symptoms of other diseases to narrow down which disease the patient presents with. The patient should be questioned about how often and to what degree headaches, visual disturbances, and symptoms associated with pituitary malfunction occur. Additionally, adrenal steroid replacement should be assessed, especially in children who have prior insufficiency associated wit

After diagnosis, it is important for patients to be continually monitored. The most common treatment for PPNAD is bilateral laparoscopic adrenalectomy; the process by which both adrenal glands are removed by a small incision.

Patients who have received this treatment will be prescribed mineralocorticoid and glucocorticoid steroids as they are no longer being naturally produced.

This is a treatment which has been used and refined since 1984.

Non-steroidal anti-inflammatory drugs (NSAIDs) can give significant relief of the symptoms. Treatment of lung cancer or other causes of hypertrophic osteoarthropathy results in regression of symptoms for some patients.

Common treatments for Nelson's syndrome include radiation or surgical procedure. Radiation allows for the limitation of the growth of the pituitary gland and the adenomas. If the adenomas start to affect the surrounding structures of the brain, then a micro-surgical technique can be adapted in order to remove the adenomas in a transsphenoidal (bone at base of the skull) process. Death may result with development of a locally aggressive pituitary tumor. However, does not commonly occur with pituitary diseases. In the rare case, ACTH-secreting tumors can become malignant. Morbidity from the disease can occur due to pituitary tissue compression or replacement, and compression of structures that surround the pituitary fossa. The tumor can also compress the optic apparatus, disturb cerebrospinal fluid flow, meningitis, and testicular enlargement in rare cases.

Hypertrophic osteoarthropathy is one of many distant effect disorders due to cancer, with lung cancer being the most common cause but also occurring with ovarian or adrenal malignancies. A distant effect disorder, or a paraneoplastic syndrome, affects distant areas and thus is not related to local compression or obstruction effects from the tumor. Other paraneoplastic syndromes include hypercalcemia, SIADH, Cushing's syndrome and a variety of neurological disorders.

The U.S. Preventive Services Task Force (USPSTF) recommend that all women 65 years of age or older be screened by bone densitometry. Additionally they recommend screening women with increased risk factors that puts them at risk equivalent to a 65‑year‑old. There is insufficient evidence to make recommendations about the intervals for repeated screening and the appropriate age to stop screening. In men the harm versus benefit of screening for osteoporosis is unknown. Prescrire states that the need to test for osteoporosis in those who have not had a previous bone fracture is unclear. The International Society for Clinical Densitometry, however, suggest BMD testing for men 70 or older, or those who are indicated for risk equal to that of a 70‑year‑old. A number of tools exist to help determine who is reasonable to test.

Cardiac myxomas can be difficult to manage surgically because of recurrence within the heart, often far away from the site of the initial tumor.

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.

Diagnosis is made first by diagnosing Cushing's syndrome, which can be difficult to do clinically since the most characteristic symptoms only occur in a minority of patients. Some of the biochemical diagnostic tests used include salivary and blood serum cortisol testing, 24-hour urinary free cortisol (UFC) testing, the dexamethasone suppression test (DST), and bilateral inferior petrosal sinus sampling (BIPSS). No single test is perfect and multiple tests should always be used to achieve a proper diagnosis. Diagnosing Cushing's disease is a multidisciplinary process involving doctors, endocrinologists, radiologists, surgeons, and chemical pathologists.

Once Cushing's syndrome has been diagnosed, the first step towards finding the cause is measuring plasma corticotropin concentrations. A concentration consistently below 1.1 pmol/L is classified as corticotropin-independent and does not lead to a diagnosis of Cushing's disease. In such cases, the next step is adrenal imaging with CT. If plasma corticotropin concentrations are consistently above 3.3 pmol/L, then corticotropin-dependent Cushing's syndrome is most likely. Any intermediate values need to be cautiously interpreted and a corticotropin-releasing hormone (CRH) test is advised in order to confirm corticotropin dependency. If corticotropin-dependent Cushing's syndrome is determined then the next step is to distinguish between Cushing's disease and ectopic corticotropin syndrome. This is done via a combination of techniques including CRH, high-dose DST, BIPSS, and pituitary MRI.

Two dexamethasone suppression tests (DSTs) are generally used, the overnight and 48-h DSTs. For both tests, a plasma cortisol level above 50 nmol/L is indicative of Cushing's disease. However, 3-8% of patients with Cushing's disease will test negative due to a retention of dexamethasone suppression abilities. For non-Cushing or healthy patients, the false-positive rate is 30%. The 48-h DST is advantageous since it is more specific and can be done by outpatients upon proper instruction. In the high-dose 48-h DST, 2 mg of dexamethasone is given every 6 hours for 48 hours or a single dose of 8 mg is given. This test is not needed if the 48-h low-dose DST has shown suppression of cortisol by over 30%. These tests are based on the glucocorticoid sensitivity of pituitary adenomas compared to non-pituitary tumors.

Administration of corticotropin releasing hormone (CRH) can differentiate this condition from ectopic ACTH secretion. In a patient with Cushing's disease, the tumor cells will be stimulated to release corticotropin and elevated plasma corticotropin levels will be detected. This rarely occurs with ectopic corticotropin syndrome and thus is quite useful for distinguishing between the two conditions. If ectopic, the plasma ACTH and cortisol levels should remain unchanged; if this is pituitary related, levels of both would rise. The CRH test uses recombinant human or bovine-sequence CRH, which is administered via a 100μg intravenous bolus dose. The sensitivity of the CRH test for detecting Cushing's disease is 93% when plasma levels are measured after fifteen and thirty minutes. However, this test is used only as a last resort due to its high cost and complexity.

A CT or MRI of the pituitary may also show the ACTH secreting tumor if present. However, in 40% of Cushing's disease patients MRI is unable to detect a tumor. In one study of 261 patients with confirmed pituitary Cushing's disease, only 48% of pituitary lesions were identified using MRI prior to surgery. The average size of tumor, both those that were identified on MRI and those that were only discovered during surgery, was 6 mm.

A more accurate but invasive test used to differentiate pituitary from ectopic or adrenal Cushing's syndrome is inferior petrosal sinus sampling. A corticotropin gradient sample via BIPSS is required to confirm diagnosis when pituitary MRI imaging and biochemical diagnostic tests have been inconclusive. A basal central:peripheral ratio of over 3:1 when CRH is administered is indicative of Cushing’s disease. This test has been the gold standard for distinguishing between Cushing's disease and ectopic corticotropin syndrome. The BIPSS has a sensitivity and specificity of 94% for Cushing's disease but it is usually used as a last resort due to its invasiveness, rare but serious complications, and the expertise required to perform it.

Another diagnostic test used is the urinary free cortisol (UFC) test, which measures the excess cortisol excreted by the kidneys into the urine. Results of 4x higher cortisol levels than normal are likely to be Cushing's disease. This test should be repeated three times in order to exclude any normally occurring periods of hypercortisolism. The UFC test has a specificity of 81% and thus has a high rate of false-positives that are due to pseudo-Cushing states, sleep apnea, polycystic ovary syndrome, familial glucocorticoid resistance, and hyperthyroidism.

The late-night or midnight salivary cortisol test has been gaining support due to its ease of collection and stability at room temperature, therefore it can be assigned to outpatients. The test measures free circulating cortisol and has both a sensitivity and specificity of 95-98%. This test is especially useful for diagnosing children.

The American neurosurgeon Harvey Cushing in 1914 reported a patient with a pituitary tumour that he had operated on. Post mortum finding were suggestive of Carney complex. this condition had yet to be described. In 2017 archived tissue from this operation were subjected to DNA sequencing. This revealed a Arg74His (Arginine to Histidine: Guanine (G)-> Adenosine (A) transition in the second codon position of the 74 codon in the protein) mutation in the PRKAR1A gene confirming the diagnosis of Carney complex. Cushing's paper appears to be the first report of this complex.

Although corticoid-to-creatinine ratios are generally higher in horses with PPID, numerous false positives and false negatives occur with this test, so it is not recommended.

There are differenct types of congenital hyperinsulinism as "diffuse and focal" indicated below:

The differential diagnosis of congenital hyperinsulinism is consistent with PMM2-CDG, as well as several syndromes. Among other DDx we find the following that are listed:

- MPI-CDG

- Beckwith-Wiedemann syndrome

- Sotos syndrome

- Usher 1 syndromes

Quantitative computed tomography differs from DXA in that it gives separate estimates of BMD for trabecular and cortical bone and reports precise volumetric mineral density in mg/cm rather than BMD's relative Z score. Among QCT's advantages: it can be performed at axial and peripheral sites, can be calculated from existing CT scans without a separate radiation dose, is sensitive to change over time, can analyze a region of any size or shape, excludes irrelevant tissue such as fat, muscle, and air, and does not require knowledge of the patient's subpopulation in order to create a clinical score (e.g. the Z-score of all females of a certain age). Among QCT's disadvantages: it requires a high radiation dose compared to DXA, CT scanners are large and expensive, and because its practice has been less standardized than BMD, its results are more operator-dependent. Peripheral QCT has been introduced to improve upon the limitations of DXA and QCT.

Quantitative ultrasound has many advantages in assessing osteoporosis. The modality is small, no ionizing radiation is involved, measurements can be made quickly and easily, and the cost of the device is low compared with DXA and QCT devices. The calcaneus is the most common skeletal site for quantitative ultrasound assessment because it has a high percentage of trabecular bone that is replaced more often than cortical bone, providing early evidence of metabolic change. Also, the calcaneus is fairly flat and parallel, reducing repositioning errors. The method can be applied to children, neonates, and preterm infants, just as well as to adults. Some ultrasound devices can be used on the tibia.

When a thymoma is suspected, a CT/CAT scan is generally performed to estimate the size and extent of the tumor, and the lesion is sampled with a CT-guided needle biopsy. Increased vascular enhancement on CT scans can be indicative of malignancy, as can be pleural deposits. Limited biopsies are associated with a very small risk of pneumomediastinum or mediastinitis and an even-lower risk of damaging the heart or large blood vessels. Sometimes thymoma metastasize for instance to the abdomen.

The diagnosis is made via histologic examination by a pathologist, after obtaining a tissue sample of the mass. Final tumor classification and staging is accomplished pathologically after formal surgical removal of the thymic tumor

Selected laboratory tests can be used to look for associated problems or possible tumor spread. These include: full blood count, protein electrophoresis, antibodies to the acetylcholine receptor (indicative of myasthenia), electrolytes, liver enzymes and renal function.

Diagnostic testing in a possible paraneoplastic syndrome depends on the symptoms and the suspected underlying cancer.

Diagnosis may be difficult in patients in whom paraneoplastic antibodies cannot be detected. In the absence of these antibodies, other tests that may be helpful include MRI, PET, lumbar puncture and electrophysiology.

Hormonal syndromes should be confirmed with laboratory testing. Laboratory findings in Cushing syndrome include increased serum glucose (blood sugar) and increased urine cortisol. Adrenal virilism is confirmed by the finding of an excess of serum androstenedione and dehydroepiandrosterone. Findings in Conn syndrome include low serum potassium, low plasma renin activity, and high serum aldosterone. Feminization is confirmed with the finding of excess serum estrogen.

An adrenal "incidentaloma" is an adrenal tumor found by coincidence without clinical symptoms or suspicion. It is one of the more common unexpected findings revealed by computed tomography (CT), magnetic resonance imaging (MRI), or ultrasonography.

In these cases, a dexamethasone suppression test is often used to detect cortisol excess, and metanephrines or catecholamines for excess of these hormones. Tumors under 3 cm are generally considered benign and are only treated if there are grounds for a diagnosis of Cushing's syndrome or pheochromocytoma. Radiodensity gives a clue in estimating malignancy risk, wherein a tumor with 10 Hounsfield units or less on an unenhanced CT is probably a lipid-rich adenoma.

Hormonal evaluation includes:

- 1-mg overnight dexamethasone suppression test

- 24-hour urinary specimen for measurement of fractionated metanephrines and catecholamines

- Blood plasma aldosterone concentration and plasma renin activity, "if hypertension is present"

On CT scan, benign adenomas typically are of low radiographic density (due to fat content) and show rapid washout of contrast medium (50% or more of the contrast medium washes out at 10 minutes). If the hormonal evaluation is negative and imaging suggests benign, followup should be considered with imaging at 6, 12, and 24 months and repeat hormonal evaluation yearly for 4 years

Adrenocortical hyperfunction is a condition where there is an overexpression of products of the adrenal cortex.

When cortisol is overproduced, it is called Cushing's syndrome.

When aldosterone is overproduced, it is called hyperaldosteronism.

Lenz–Majewski syndrome is a skin condition characterized by hyperostosis, craniodiaphyseal dysplasia, dwarfism, cutis laxa, proximal symphalangism, syndactyly, brachydactyly, mental retardation, enamel hypoplasia, and hypertelorism.

In 2013, whole-exome sequencing showed that a missense mutation resulting in overactive phosphatidylserine synthase 1 was the cause of LMS, making it the first known human disease to be caused by disrupted phosphatidylserine metabolism. The researchers suggested a link between the condition and bone metabolism.

Visual fields associated with chiasmal syndrome usually leads to an MRI. Contrast can delineate arterial aneurysms and will enhance most intrinsic chiasmal lesions. If a mass is confirmed on MRI, an endocrine panel can help determine if a pituitary adenoma is involved.

In patients with functional adenomas diagnosed by other means, visual field tests are a good screen to test for chiasmal involvement. Visual fields tests will delinate chiasmal syndromes because the missing fields will not cross the midline. Junctional scotomas classically show ipsilateral optic disc neuropathy with contralateral superotemporal defects. Bitemporal hemianopia with or without central scotoma is present if the lesions have affected the body of the chiasm. A posterior chiasm lesion should only produce defects on the temporal sides of the central visual field.

No major organization recommends universal screening for diabetes as there is no evidence that such a program improve outcomes. Screening is recommended by the United States Preventive Services Task Force (USPSTF) in adults without symptoms whose blood pressure is greater than 135/80 mmHg. For those whose blood pressure is less, the evidence is insufficient to recommend for or against screening. There is no evidence that it changes the risk of death in this group of people. They also recommend screening among those who are overweight and between the ages of 40 and 70.

The World Health Organization recommends testing those groups at high risk and in 2014 the USPSTF is considering a similar recommendation. High-risk groups in the United States include: those over 45 years old; those with a first degree relative with diabetes; some ethnic groups, including Hispanics, African-Americans, and Native-Americans; a history of gestational diabetes; polycystic ovary syndrome; excess weight; and conditions associated with metabolic syndrome. The American Diabetes Association recommends screening those who have a BMI over 25 (in people of Asian descent screening is recommended for a BMI over 23).