What is the reference range for Diurnal cortisol decline?

The standard reference range for Diurnal cortisol decline is Morning cortisol typically ≥1.5–2× afternoon value; loss of this gradient is abnormal.. Reference ranges vary by laboratory and assay platform — interpret in context of the issuing laboratory's stated range.

Which tests measure Diurnal cortisol decline?

Diurnal cortisol decline is measured in 1 test on BiomarkersLabs.com, including Cortisol, 2 Specimens.

Biomarker Reference · AM:PM ratio

What does the Diurnal cortisol decline test measure?

Diurnal cortisol decline (AM:PM ratio) is a clinical biomarker used in adrenal-stress assessment. The ratio or absolute difference between morning and afternoon cortisol quantifies preservation of the circadian rhythm. It is measured in 1 laboratory test on BiomarkersLabs.com.

Reference Range: Morning cortisol typically ≥1.5–2× afternoon value; loss of this gradient is abnormal.
Units: ratio
Measured In: 1 test
Category: Adrenal

Functional medicine optimalNo fixed optimal ratio; interpretation is qualitative. A clear gradient (morning > afternoon by ≥30–50%) reflects healthy circadian control.

What is Diurnal cortisol decline?

The ratio or absolute difference between morning and afternoon cortisol quantifies preservation of the circadian rhythm. In intact hypothalamic-pituitary-adrenal regulation the morning level is substantially higher than the afternoon level; flattening of this gradient occurs when cortisol secretion becomes autonomous or when the negative-feedback loop is disrupted.

Why is Diurnal cortisol decline measured?

A preserved diurnal decline argues against Cushing syndrome and confirms that a low morning cortisol is not simply a timing artefact. Loss of decline — particularly if the afternoon value equals or exceeds the morning — is one of the earliest biochemical features of autonomous hypersecretion and warrants further dynamic testing.

Reference ranges

Standard reference: Morning cortisol typically ≥1.5–2× afternoon value; loss of this gradient is abnormal.
Functional medicine optimal: No fixed optimal ratio; interpretation is qualitative. A clear gradient (morning > afternoon by ≥30–50%) reflects healthy circadian control.
Units: ratio

Reference ranges vary by laboratory and assay platform. Interpret in context of the issuing laboratory's stated range.

Tests that measure Diurnal cortisol decline

1 test on BiomarkersLabs.com include this biomarker.

BML-ADR-029Comprehensive

Cortisol, 2 Specimens

Diurnal cortisol decline reference range in this test: Morning cortisol typically ≥1.5–2× afternoon value; loss of this gradient is abnormal.

Related clinical conditions

Related Biomarkers

Frequently measured alongside

Cortisol (morning, ~30 minutes post-waking)Cortisol-AM5 tests Cortisol (afternoon specimen)Cortisol PM4 tests

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