It is important not to stop prescribed steroid medications on your own. Abrupt withdrawal after long-term use can cause adrenal insufficiency.<\/p>\n
![\"Circadian](\"https:\/\/medilab.km.ua\/wp-content\/uploads\/2026\/11\/dobovyj-rytm-kortyzolu-pry-syndromi-kushynga.jpg\")
<\/p>\n
Cortisol lives by its own biological clock<\/h2>\n
This is where the diagnosis of Cushing's syndrome becomes unusual.<\/p>\n
Most laboratory tests are based on the concentration of a substance at a given point in time. For cortisol, this is often not enough, as its production depends on the time of day.<\/p>\n
In a person with a normal sleep schedule, cortisol levels are typically highest in the morning hours and gradually decline in the evening and night. This is part of a normal circadian rhythm.<\/p>\n
In Cushing's syndrome, this rhythm can be disrupted. Cortisol remains elevated at a time when its concentration should normally be low.<\/p>\n
Therefore, for diagnosis, studies are used that evaluate not just the amount of the hormone, but various features of its secretion.<\/p>\n
What Cortisol in Late Evening Saliva Tells Us<\/h3>\n
One recommended method is to measure saliva cortisol late in the evening, usually closer to your usual bedtime.<\/p>\n
This test helps detect loss of normal nocturnal hormone decline. At least two measurements are usually recommended for initial diagnosis.<\/p>\n
In many cases, the sample can be collected at home according to the laboratory's instructions. However, the exact time, collection procedures, and storage conditions are important.<\/p>\n
The result may be more difficult to interpret if the person works night shifts, has an unstable sleep pattern, has recently changed time zones, or was under severe stress immediately before the material was collected.<\/p>\n
Therefore, studies cannot be mechanically assigned to everyone on the same schedule.<\/p>\n
Why is daily urine needed?<\/h3>\n
Another way to assess excess cortisol is to measure the amount of free cortisol excreted in the urine over a 24-hour period.<\/p>\n
Unlike a single blood test, this test reflects hormone secretion over a longer period. It is useful for detecting excessive cortisol production, but it also has limitations.<\/p>\n
For a reliable result, it is necessary to properly collect all urine over a specified period of time. Missed portions or violation of storage rules can affect the accuracy of the study.<\/p>\n
Due to natural fluctuations in cortisol secretion, at least two separate daily sessions are usually performed.<\/p>\n
In cases of significant renal impairment, the value may be less informative. In addition, moderate elevations in free cortisol are possible in conditions not associated with Cushing's syndrome.<\/p>\n
The role of this research is discussed in more detail in the material on cortisol in urine<\/a>.<\/p>\n The third important method is based on a different principle.<\/p>\n Dexamethasone is a synthetic glucocorticoid that normally suppresses the production of ACTH and, accordingly, reduces the secretion of its own cortisol.<\/p>\n During an overnight dexamethasone test, the patient takes a doctor-determined dose of the drug in the evening and donates blood the next morning to measure cortisol.<\/p>\n If the hormonal feedback system is working normally, cortisol should decrease significantly after dexamethasone.<\/p>\n A common diagnostic criterion is a cortisol level greater than 1.8 mcg\/dL, or 50 nmol\/L, after an overnight test with 1 mg dexamethasone that requires further evaluation. This does not automatically confirm Cushing's syndrome.<\/p>\n The result may be altered by some anticonvulsants, estrogen-containing drugs, pregnancy, impaired absorption or metabolism of dexamethasone. Sometimes, for clarification, the doctor prescribes a measurement of the concentration of dexamethasone itself.<\/p>\n The test is performed as prescribed by a doctor. You should not take dexamethasone to test cortisol on your own.<\/p>\n These tests do not completely duplicate each other. They check for different hormonal system disorders.<\/p>\n Late evening salivary cortisol helps assess circadian rhythm. Diurnal urine reflects total free cortisol excretion. Dexamethasone test shows how the mechanism of suppression of hormonal secretion works.<\/p>\n When the results are consistent, the doctor gets a much more convincing picture than from a single random analysis.<\/p>\n The Endocrine Society's recommendations suggest using these methods for initial diagnosis and additional testing after the first abnormal result.<\/p>\n At the same time, a routine morning blood test for cortisol<\/a> or a single ACTH test is not recommended as a stand-alone screening for Cushing's syndrome.<\/p>\n This is a fundamental difference from many other endocrine disorders: it is not just the elevated hormone that matters, but the nature of its secretion.<\/p>\n In medical practice, there are conditions that may be accompanied by excessive activation of the cortisol regulatory system, but are not true endogenous Cushing's syndrome.<\/p>\n Such conditions include severe or prolonged physiological stress, some mental disorders, alcohol abuse, poorly controlled diabetes, and other diseases.<\/p>\n Sometimes the term "pseudo-Cushing's" is used to describe them, although more recent literature more often refers to non-neoplastic hypercorticism.<\/p>\n Distinguishing between these conditions can be difficult, especially when a patient is overweight, has high blood pressure, sleep disturbances, or elevated glucose, but does not have the more specific manifestations of Cushing's syndrome.<\/p>\n Therefore, an elevated screening test result usually requires confirmation by another method rather than immediate diagnosis.<\/p>\n There is another feature that can cause Cushing's syndrome to go unnoticed.<\/p>\n In a small proportion of patients, excess cortisol production is cyclical. Periods of elevation may alternate with intervals when hormone levels return to normal.<\/p>\n If the analysis is performed during such a period, the result may not reflect a violation.<\/p>\n In 2021, the international consensus on the diagnosis and treatment of Cushing's disease emphasized the special role of repeated measurements of late evening salivary cortisol in suspected cyclic hypercorticism.<\/p>\n This does not mean that everyone with normal cortisol levels needs to be retested. Repeat testing is only appropriate when clinical signs are consistent, progressing, or when results from different tests are conflicting.<\/p>\n One of the features of correct diagnosis is consistency.<\/p>\n First, you need to establish that the body is indeed producing excess cortisol. And only then can you determine the cause.<\/p>\nWhy check the reaction to dexamethasone?<\/h3>\n
Why three different methods look for the same disease<\/h2>\n
When cortisol is elevated but Cushing's syndrome is not present<\/h2>\n
Why do we sometimes have to go back for an examination?<\/h2>\n
Only after confirmation do they start looking for the source of cortisol<\/h2>\n