Cortisone (U4 Bedtime) Test

Your body has a built-in rhythm for the stress hormone cortisol. It should surge in the morning to wake you up and fall to its lowest point at bedtime, when your body shifts into rest and repair. A bedtime urine sample captures whether that nighttime low is actually happening, or whether your stress system is still running when it should be quiet.

This test measures cortisone, the inactive partner of cortisol, in a dried urine sample collected before sleep. A high reading at bedtime can be an early signal of subtle cortisol excess, disrupted circadian rhythm, or shift-work biology that standard daytime blood tests often miss.

What This Test Actually Measures

Cortisone is a steroid molecule produced when the kidney and other tissues deactivate cortisol, the active stress hormone. The two forms are constantly interconverted by enzymes called 11-beta-hydroxysteroid dehydrogenases (11-beta-HSD): one enzyme switches cortisol off into cortisone, and another switches cortisone back on into cortisol. Urinary cortisone reflects how much active cortisol your body has been producing and processing, particularly through the kidneys.

The U4 bedtime sample is the fourth and final collection in a dried urine panel, taken just before sleep. Because cortisol normally bottoms out at night, this is the most sensitive window to detect a stress system that is not properly winding down. A bedtime cortisone level that is too high suggests your hypothalamic-pituitary-adrenal axis (the brain-to-adrenal-gland signaling chain that controls cortisol) is failing to quiet down for sleep.

Why the Bedtime Reading Matters Most

In healthy biology, cortisol and cortisone show a strong day-night swing. Loss of that swing, a flattened slope, or an elevated evening value is the signature finding in subclinical hypercortisolism and in disrupted circadian biology from shift work, chronic stress, and sleep disruption. The bedtime sample isolates the part of the curve where abnormalities show up first.

Salivary cortisone, a closely related bedtime measure, has been validated as an accurate stand-in for free cortisol and tracks the biologically active fraction of the hormone. It is unaffected by changes in cortisol-binding proteins, which can make blood cortisol misleading in women on oral estrogens, in pregnancy, or in liver disease. Urinary cortisone in a bedtime sample reflects the same underlying biology: cumulative free cortisol exposure at the time your body should be at rest.

Subclinical Cortisol Excess

The most actionable use of a bedtime cortisone measurement is catching mild, subclinical cortisol excess, often called mild autonomous cortisol secretion. People with this condition do not look like classic Cushing's syndrome on the outside, but they have abnormal steroid patterns including higher nocturnal steroid production and elevated evening free cortisol.

In a study of 94 people with adrenal incidentalomas (small adrenal tumors found by chance on imaging), those with mild autonomous cortisol secretion showed an abnormal urine steroid metabolome with a high glucocorticoid-to-androgen ratio and elevated nighttime steroid output compared to people without the condition. In another cohort, 9 out of 10 patients with autonomous cortisol secretion had elevated late-night salivary cortisone, compared with only 9% of people with non-functioning adrenal lesions. This is exactly the population where a normal daytime cortisol blood draw can look reassuring while the nighttime number tells a different story.

Heart, Blood Pressure, and Blood Sugar Risk

Higher nighttime glucocorticoid exposure is linked to the conditions most people are trying hardest to prevent. In a cross-sectional study of 6,931 older adults, the ratio of urinary cortisol to cortisone modified the link between type 2 diabetes and high blood pressure, suggesting the balance between the two forms helps determine cardiometabolic risk. Subclinical hypercortisolism itself, the condition this kind of testing helps detect, has been associated in pooled analyses with a higher prevalence of cardiometabolic disease and mortality, though the causal arrow is still being worked out.

Studies of the broader cortisol rhythm reinforce the point. In the Whitehall II cohort of 4,047 adults, flatter day-to-night cortisol slopes were associated with higher all-cause mortality, particularly from cardiovascular causes. In the KORA-F3 study of 1,090 people, disrupted day-night cortisol patterns also tracked with cardiovascular death. A bedtime cortisone reading that fails to dip is one of the clearest signs that this protective rhythm has been lost.

Bone Loss

Nighttime glucocorticoid exposure has a specific effect on bone. In a study of patients receiving hydrocortisone therapy, higher total and night-time cortisone and glucocorticoid metabolites were associated with lower markers of bone formation, suggesting nocturnal exposure may have a greater impact on bone turnover than daytime exposure. In a meta-analysis of adrenal adenomas with mild autonomous cortisol secretion, people with this pattern had roughly 1.5 to 2 times the odds of fractures and osteoporosis compared to those with non-functioning adenomas. A bedtime cortisone reading is one of the earliest signals that bone may be quietly losing ground.

Mood and Cognition

The same nighttime cortisol signal that affects metabolism and bone also reaches the brain. In a study of major depressive disorder, dysregulation of the cortisol axis with elevated morning cortisol and a blunted cortisol awakening response was a consistent feature. In a study of more than 4,000 adults, genetic variants that raised the cortisol nadir were associated with higher risk of incident depression. A meta-analysis of cortisol in Alzheimer's disease found that morning cortisol levels were moderately elevated in people with Alzheimer's, supporting a potential diagnostic and prognostic role. The bedtime cortisone reading is the most direct window onto whether the brain's stress brake is engaging at night.

Research-Reported Ranges

This is an emerging marker. There are no universally standardized clinical cutpoints for bedtime urinary cortisone specifically, and the values reported by your lab depend on the assay (most modern panels use mass spectrometry, abbreviated LC-MS/MS, which separates molecules by mass) and how the result is normalized to urinary creatinine. The most useful published reference data come from a study of 1,128 adults that established population-based reference intervals for urinary steroid metabolites and confirmed that values vary by sex, age, and time of day. Values from this study are illustrative orientation only, not universal targets, because your lab will likely report slightly different numbers, possibly in different units.

Compare your results within the same lab over time for the most meaningful trend. A single isolated bedtime reading should not drive a clinical decision in isolation.

Why One Reading Is Not Enough

Cortisol biology is unusually noisy from day to day. A review of cortisol in chronic kidney disease described the volatility of morning cortisol levels and the high measurement variability that comes with such a narrow timing window. In a study of post-dexamethasone cortisol in 1,129 people with adrenal incidentalomas, roughly 15% of the variability was attributed to measurement noise, with most variability unexplained by any known factor. A single bedtime cortisone reading is a snapshot of a system that fluctuates with sleep quality, stress, illness, and timing.

The right approach is to treat one reading as a starting point, not a verdict. Get a baseline now, repeat in 3 to 6 months if you are making targeted changes (better sleep, shift schedule adjustments, stress work), and then at least annually after that. Trends across multiple bedtime samples are far more meaningful than a single value, especially because a flattened day-night slope, not just an absolute number, is what predicts long-term cardiometabolic risk.

When Results Can Be Misleading

Several factors can shift a single bedtime cortisone reading without reflecting true changes in your stress biology:

• Kidney function: reduced kidney filtration changes how cortisol and cortisone are cleared and excreted. In studies of chronic kidney disease, lower filtration rate was associated with altered cortisol dynamics including blunted day-night slopes and reduced urinary cortisol excretion despite higher circulating levels.
• Age and body weight: in a study of 1,129 adults, cortisol after dexamethasone suppression rose about 11% per decade of age and was higher in people with a body mass index under 30. The same patterns likely apply to nighttime cortisone.
• Acute illness, surgery, or major stress in the days before testing: these can transiently raise the entire cortisol axis and distort a bedtime reading, even if your baseline biology is normal.
• Collection timing and contamination: a urine sample taken hours before actual bedtime, or contaminated with food, drink, or recent topical steroid use on the skin, can produce misleading values.

What to Do With an Abnormal Result

An elevated bedtime cortisone reading is not a diagnosis. The next step is to confirm the pattern with a repeat dried urine collection, ideally a full four-point series so you can see the whole curve. If the bedtime elevation persists, it is worth pairing with a late-night salivary cortisol or cortisone measurement and an overnight dexamethasone suppression test. In one study of suspected Cushing's syndrome, combining late-night salivary cortisone with late-night salivary cortisol gave an AUC (a statistical measure of test accuracy, where 1.0 is perfect) of 0.95 for Cushing's disease, outperforming the overnight dexamethasone suppression test alone (AUC 0.74).

If the pattern points to mild autonomous cortisol secretion or circadian disruption, an endocrinologist is the right specialist to involve. If your bedtime values are persistently low across multiple readings and your waking value is also low, evaluation for adrenal insufficiency is appropriate, again under endocrinology guidance. A single high or low reading in isolation rarely warrants treatment, but a consistent pattern, especially alongside high blood pressure, weight gain, or bone loss, deserves a structured workup.