Cortisol (U3 Dinner) Test

Your stress hormone is supposed to be high in the morning and low by evening. When that evening drop fails, it is one of the earliest signs that the system controlling stress, metabolism, and sleep is running off-rhythm. A dinnertime urine sample captures the active, unbound fraction of cortisol your body is putting into circulation when most people are winding down.

This is a research-style measurement, not a single number with a textbook cutpoint. Used alongside the morning and bedtime samples in a four-point urine collection, it helps build a picture of your cortisol curve across the day. That curve, more than any one value, is what links cortisol to long-term health risks.

What This Test Actually Measures

Cortisol is a steroid hormone (glucocorticoid) made in the outer layer of the adrenal glands, two small glands that sit on top of your kidneys. Its release is controlled by a feedback loop between the brain and the adrenals (the HPA axis, short for hypothalamic-pituitary-adrenal axis). Levels normally peak shortly after waking and decline through the day to a low point around midnight.

Most blood tests measure total cortisol, which is mostly bound to carrier proteins and not biologically active. Dried urine captures the free, active fraction your tissues actually see, and it does so cumulatively over the hours leading up to the collection. The dinnertime sample (typically the third of four daily collections in a DUTCH-style protocol) reflects the descending part of your daily curve.

Why the Evening Number Matters

A flat or elevated evening cortisol is a marker of a disrupted day-night rhythm, which research has linked to a wide range of health outcomes. A flatter slope across the day is associated with poorer mental and physical health, with the largest effects seen for immune and inflammation outcomes. In the Whitehall II study of 4,047 civil servants, people with flatter cortisol declines across the day had higher all-cause mortality, particularly from cardiovascular deaths.

Chronic kidney disease, ovarian cancer survival, and cardiovascular disease incidence have all been linked to disrupted diurnal cortisol patterns in observational research. Evening elevation is also a recognized feature of interferon-alpha therapy and chronic stress states.

Cushing's Syndrome and Mild Autonomous Cortisol Secretion

The strongest clinical use case for late-day cortisol is detecting cortisol excess. Late-night salivary cortisol (the closest standardized analogue to an evening urine measure) has roughly 90% sensitivity and 96% specificity for Cushing's syndrome at a 23:00 cutoff of 3.6 nmol/L. Late-night salivary cortisone in the same study reached 100% sensitivity and 95% specificity.

Mild autonomous cortisol secretion, or MACS (a milder, often symptomless form of cortisol excess found in some adrenal nodules), is associated with higher rates of diabetes, hypertension, dyslipidemia, and all-cause mortality compared with non-functioning adrenal tumors. In a study of 1,305 people with benign adrenal tumors, those with MACS had a higher prevalence of high blood pressure and type 2 diabetes.

Cardiometabolic Risk

Long-term elevated cortisol exposure tracks with metabolic syndrome features (larger waistline, higher triglycerides, higher blood pressure) and with cardiovascular disease incidence and prognosis. A study of 1,405 adults found that long-term hair cortisone levels were associated with metabolic syndrome, particularly in younger people. Hair measurements reflect months of exposure rather than the single-day window urine captures, but the underlying biology, persistent HPA activation, is the same process a flat evening urine cortisol can flag.

Brain Health and Cognition

Elevated cortisol has been linked to poorer cognition, faster cognitive decline, and increased risk of dementia and Alzheimer's disease, with hippocampal damage proposed as one mechanism. Higher cerebrospinal fluid cortisol is associated with faster cognitive decline in Alzheimer's disease. These findings come mostly from blood, saliva, and CSF cortisol measurements rather than urine specifically, so they describe the same hormone but a different matrix than this test.

Mental Health

Depression, bipolar disorder, psychosis, and PTSD often show elevated cortisol, and normalization tends to parallel clinical improvement. Hair cortisol concentration tracks psychiatric symptom severity and response to treatment in some studies. As with cognition, most of this evidence comes from blood, saliva, or hair rather than dinnertime urine, so it supports the broader biology but does not pin a specific number on this assay.

Reference Ranges

There is no universal clinical cutpoint for dinnertime dried urine cortisol. Most published reference data for evening cortisol comes from salivary studies (the CIRCORT meta-dataset of 104,623 samples provided age- and sex-specific percentiles for diurnal saliva), and from urine collected over 24 hours rather than in timed dried-urine spots. Treat the numbers below as analytical orientation, not diagnostic thresholds.

For context, 24-hour urinary free cortisol upper reference limits (measured by mass spectrometry in 4,950 adults) were 238 nmol/day in men and 147 nmol/day in women. Late-night salivary cortisol cutoffs for Cushing's screening sit around 3.6 nmol/L at 23:00. Your lab will use its own assay-specific ranges, and these will not match the salivary or 24-hour values directly.

Compare your results within the same lab over time. Different labs use different assays, different collection windows, and different normalization methods, and the numbers are not interchangeable.

Why One Reading Is Not Enough

Cortisol fluctuates more than almost any other hormone in your body. Acute stress, sleep loss, recent exercise, and even a difficult morning can shift a single value. Repeated acute stress over several days can blunt the cortisol awakening response while leaving baseline waking values intact, which means one day's collection can look unrepresentative of your usual pattern.

Get a baseline four-point curve, retest in 3 to 6 months if you are making targeted changes (sleep, stress practices, exercise dose), and at least annually thereafter. The shape of the curve over time, especially whether your evening value drops as it should, is more informative than any single dinnertime number.

When Results Can Be Misleading

Four factors can distort a single dinnertime reading enough to lead you to the wrong conclusion:

• Recent acute stress or poor sleep: a stressful afternoon, an argument, or a bad night before the collection can elevate the evening sample without indicating a chronic problem.
• Oral estrogens and combined oral contraceptives: ethinylestradiol-based contraceptives raise total cortisol substantially (around 668 nmol/L higher) by increasing cortisol-binding globulin, with users showing roughly 0.9 log2 units higher circulating cortisol. Free cortisol (what dried urine reflects) is less affected, but the effect is not zero.
• Recent intense exercise: prolonged endurance exercise raises cortisol; pre- and mid-exercise carbohydrate intake of 30 g per hour or more attenuates the rise.
• Collection timing errors: a sample collected an hour too early or too late shifts which part of the curve you have captured.

What to Do With an Abnormal Result

A high or non-suppressed dinnertime cortisol is not a diagnosis. It is a signal to investigate further. Pair it with the rest of the four-point curve (morning, mid-morning, dinner, bedtime) to see whether the entire rhythm is shifted or only the evening point. Add an ACTH level and a 1 mg overnight dexamethasone suppression test if you want to rule out cortisol excess seriously; failure to suppress below 1.8 micrograms per deciliter on the dexamethasone test is the classic screening threshold for cortisol excess. If your morning cortisol is low and evening is also blunted, the question shifts toward adrenal insufficiency, and a cosyntropin stimulation test becomes the relevant next step.

An endocrinologist is the right specialist to involve if any of these patterns appear consistently across repeat testing, if you have an adrenal nodule on imaging, or if you have unexplained weight gain, easy bruising, muscle weakness, new-onset diabetes, or hypertension that is hard to control.