Understanding Lab Tests for Cushing's Syndrome
Written by Private MD Labs Medical Writing Team • Last Updated: September 8, 2025
Cushing's Syndrome is a hormonal disorder caused by prolonged exposure to high levels of cortisol, often called the 'stress hormone.' This condition can lead to various symptoms including high blood pressure, abdominal obesity, fatigue, muscle weakness, and elevated blood sugar levels.
Top Recommended Test
Cortisol, Total
This is a key diagnostic test that measures total cortisol levels in the blood. Cushing's syndrome is directly caused by prolonged exposure to high cortisol levels, making this test essential for confirming the diagnosis and monitoring cortisol overproduction by the adrenal glands.
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How Blood Tests Diagnose Cushing's Syndrome
Blood tests are the primary diagnostic tools for Cushing's Syndrome, as they can directly measure cortisol levels and assess related hormonal imbalances. These tests evaluate the body's cortisol production patterns and identify metabolic complications associated with excess cortisol exposure.
Other Primary Diagnostic Tests
Cortisol, AM
This test measures morning cortisol levels when they should naturally be at their highest. Elevated AM cortisol values are a strong indicator of Cushing's syndrome, as the condition disrupts the normal cortisol rhythm and maintains persistently high levels.
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Supporting Hormonal Tests
Dehydroepiandrosterone (DHEA-s) Sulfate
This test measures DHEA-S levels, which can be elevated in Cushing's syndrome. Since both cortisol and DHEA-S are produced in the adrenal glands, abnormal DHEA-S levels may indicate adrenal dysfunction associated with the condition.
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DHEA (Dehydroepiandrosterone), Unconjugated, LC/MS/MS
Elevated DHEA levels can indicate Cushing's syndrome and may suggest the presence of an adrenal tumor causing overproduction of various adrenal hormones, including both DHEA and cortisol.
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Pregnenolone, LC/MS
As a precursor hormone to cortisol, abnormal pregnenolone levels can reflect the disrupted hormone production pathway seen in Cushing's syndrome, where high cortisol levels may be accompanied by elevated pregnenolone.
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Testosterone, Free, LC/MS/MS
Cushing's syndrome often results in decreased testosterone levels because high cortisol can inhibit testosterone production. This test helps assess the hormonal imbalances caused by excess cortisol.
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Testosterone, Free and Total, LC/MS/MS
Low levels of both free and total testosterone are commonly associated with Cushing's syndrome due to cortisol's suppressive effect on testosterone production, making this comprehensive test valuable for diagnosis.
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Metabolic Complication Tests
Insulin, Fasting
High cortisol levels in Cushing's syndrome can cause insulin resistance and elevated insulin levels. This test helps identify diabetes-related complications that commonly develop with prolonged cortisol exposure.
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Insulin, Free (Bioactive)
This test measures bioactive insulin levels, which can be elevated due to insulin resistance caused by excess cortisol. It provides insight into the metabolic dysfunction associated with Cushing's syndrome.
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C-Peptide, Serum
C-peptide levels can be increased in Cushing's syndrome as a result of insulin resistance and compensatory insulin production triggered by high cortisol levels.
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Potassium, Serum
Cushing's syndrome often causes low potassium levels due to excessive production of mineralocorticoids, which lead to potassium loss from the body. Monitoring potassium is important for managing complications.
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Potassium, RBC
This test measures potassium levels within red blood cells and can help identify the cellular effects of potassium depletion commonly seen in Cushing's syndrome.
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Carbon Dioxide
Cushing's syndrome can result in metabolic alkalosis, leading to increased blood CO2 levels. This test helps identify acid-base imbalances caused by the hormonal disorder.
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Important Considerations
Diagnosing Cushing's Syndrome typically requires multiple tests over time, as cortisol levels can fluctuate. Your healthcare provider may recommend additional specialized tests or repeat testing to confirm the diagnosis. The information provided here is for educational purposes only and should not replace professional medical advice.
