ASP with CAR
The ASP with CAR panel measures salivary free cortisol at awakening, 30 minutes post-awakening, afternoon, and evening to characterise the cortisol awakening response and diurnal slope. It is used to assess HPA axis dysregulation, chronic stress, burnout, mood disorders, and circadian rhythm disturbances through non-invasive home collection.
5
Biomarkers
Saliva
Sample
7–10 business days
Turnaround
Partial (see notes)
Fasting
What is the ASP/CAR test?
The ASP with CAR panel measures salivary free cortisol at four strategic time points across the day — awakening, 30 minutes post-awakening, afternoon, and evening — to characterise both the cortisol awakening response and the diurnal slope. Salivary cortisol reflects the biologically active, unbound hormone and is collected non-invasively at home, making it particularly suited to capturing the dynamic, context-sensitive behaviour of the HPA axis under real-world conditions. Practitioners order this panel to investigate suspected HPA axis dysregulation, chronic stress, burnout, atypical depression, post-traumatic stress disorder, and disorders of the circadian rhythm. Unlike single-point serum cortisol, the multi-point salivary profile reveals whether the morning surge is preserved, whether the diurnal decline is intact, and whether evening cortisol is inappropriately elevated. The CAR component adds specificity for stress-related and mood disorders, where blunted or exaggerated awakening responses have been documented, and the full-day slope helps differentiate primary adrenal pathology from central HPA dysfunction or functional dysregulation.
What does the ASP/CAR test measure?
Cortisol secretion follows a robust circadian rhythm driven by the suprachiasmatic nucleus and the hypothalamic-pituitary-adrenal axis. Upon awakening, cortisol begins to rise sharply within minutes, peaking 30–45 minutes later in the cortisol awakening response. The awakening sample captures the nadir just before this surge and anchors interpretation of the subsequent CAR slope.
The awakening cortisol level establishes baseline HPA tone at the start of the day. A very low awakening value may signal adrenal insufficiency or HPA axis hypofunction, whilst an unusually high level can reflect chronic stress, anxiety, or anticipatory arousal. It is not interpreted in isolation but rather as the reference point for the cortisol awakening response.
This sample captures cortisol near the anticipated peak of the cortisol awakening response, reflecting both basal HPA axis activity and the acute stress-preparedness surge that occurs in the first half-hour of wakefulness.
The 30-minute post-awakening cortisol is used to calculate the absolute CAR increment and to assess whether the normal morning surge is preserved, blunted, or exaggerated. An absent or flat response may indicate HPA axis exhaustion or dysregulation, whilst an excessive rise can accompany chronic stress or anxiety disorders.
The CAR is a derived parameter calculated as the absolute or percentage change in cortisol from the awakening sample to the 30-minute sample. It represents the HPA axis's acute reactive capacity and is modulated by sleep quality, anticipatory stress, light exposure, and psychosocial factors.
A preserved CAR indicates intact HPA axis reactivity and is associated with better stress resilience and cognitive readiness. A blunted CAR has been linked to chronic stress, burnout, atypical depression, and post-traumatic stress disorder, whilst an exaggerated response may accompany anxiety, major depression, and perceived chronic stress. The pattern must be interpreted in the context of the patient's sleep, mental health, and circadian habits.
Cortisol declines progressively across the day, reaching intermediate levels by mid-to-late afternoon. This sample captures the descending limb of the diurnal curve and reflects the transition from daytime alertness toward evening quiescence.
An abnormally elevated afternoon cortisol may indicate chronic HPA axis activation, loss of normal circadian rhythm, or Cushing syndrome (when very high and persistent). A very low afternoon value can reflect adrenal insufficiency or HPA axis hypofunction, though single time points are less sensitive than dynamic or serial profiles.
By late evening, cortisol reaches its nadir under normal circadian control, permitting melatonin secretion and the onset of restorative sleep. The evening sample is the most sensitive single time point for detecting loss of diurnal rhythm and mild hypercortisolism.
An elevated evening cortisol disrupts sleep onset and maintenance and is the hallmark of circadian dysregulation in Cushing syndrome, though milder elevations are common in chronic psychological stress, shift work, and sleep disorders. A normal evening nadir reassures that the circadian axis is intact.
Why is the ASP/CAR test ordered?
- Evaluation of suspected HPA axis dysregulation in patients with chronic fatigue, burnout, or stress-related symptoms not explained by other pathology
- Assessment of the cortisol awakening response in patients with atypical depression, post-traumatic stress disorder, or chronic anxiety where blunted or exaggerated CAR patterns have been described
- Investigation of suspected adrenal insufficiency or subclinical hypoadrenalism, where a flattened diurnal curve or low awakening cortisol may prompt further dynamic testing
- Screening for loss of circadian rhythm and mild hypercortisolism in patients with insomnia, weight gain, or features suggestive of Cushing syndrome, where an elevated evening cortisol is the most sensitive single marker
- Monitoring of patients undergoing stress-reduction, lifestyle, or chronotherapeutic interventions, where serial profiles track restoration of diurnal rhythm and CAR
- Functional-medicine assessment of stress resilience, HPA axis reserve, and circadian health in the context of integrative or preventive care programmes
- Work-up of shift workers, frequent travellers, or patients with circadian rhythm sleep disorders, where the diurnal pattern is expected to be disrupted
- Paediatric and adolescent evaluation of stress-related disorders, where non-invasive salivary collection is preferred over venepuncture for serial time points
Sample collection and turnaround
Sample type
Saliva
Fasting required
Partial (see notes)
Collection method
At-home collection kit
Turnaround
7–10 business days
Collection notes
Patients collect saliva at four time points using passive drool or absorbent swabs supplied in the home collection kit: immediately upon awakening (before rising), exactly 30 minutes after awakening, mid-to-late afternoon (typically 16:00–17:00), and late evening before bed (typically 22:00–23:00). The awakening and 30-minute samples must be collected before eating, drinking (except water), brushing teeth, or smoking. Patients record the exact time of each collection and note any deviations. Samples are stable at room temperature for mailing and should be returned promptly in the prepaid envelope.
Specimen requirements
Minimum 1–2 mL total saliva per time point, free of blood contamination. Patients should avoid vigorous mouth rinsing and wait at least 10 minutes after drinking water before collecting. Note any medications, especially corticosteroids, and sleep quality on the collection day.
What can affect ASP/CAR results?
The cortisol awakening response is tightly time-locked to the moment of awakening; even a 10–15 minute delay in the first sample or deviation from the 30-minute interval can distort the CAR calculation and misclassify the pattern.
Poor sleep, sleep deprivation, and night-time awakenings suppress the CAR and flatten the diurnal slope; the night before collection should be typical and reasonably restful for representative results.
Eating, drinking caffeinated beverages, or smoking shortly before or between samples can acutely raise salivary cortisol and distort the profile; patients are instructed to avoid these until after the morning samples.
Moderate to vigorous exercise acutely stimulates cortisol secretion; patients should avoid strenuous activity on the morning of collection.
Oral, inhaled, or topical corticosteroid use suppresses endogenous ACTH and alters both the diurnal pattern and the CAR; a washout period or interpretation in the context of replacement therapy is required.
Acute stressors activate the HPA axis and can elevate cortisol at all time points; the panel should be deferred during acute illness or performed serially to separate transient from chronic dysregulation.
What do ASP/CAR results mean?
Elevated
Elevated awakening and/or 30-minute cortisol, an exaggerated CAR (>160–200%), or a persistently elevated afternoon and evening cortisol with loss of the normal nadir suggest chronic HPA axis activation, chronic stress, anxiety disorders, or mild hypercortisolism. Very high evening cortisol should prompt consideration of Cushing syndrome and confirmatory testing. An isolated elevated CAR may reflect anticipatory stress or major depression.
Normal
A preserved CAR (50–160% rise), a clear descending diurnal slope with afternoon cortisol lower than awakening, and a low evening nadir (<3–5 nmol/L) indicate intact HPA axis function and circadian rhythm. This pattern reassures that the stress response and circadian biology are functioning appropriately.
Reduced
A low awakening cortisol with a blunted or absent CAR (<50% rise) and low afternoon and evening values raise concern for adrenal insufficiency or severe HPA axis hypofunction and warrant confirmatory dynamic testing (ACTH stimulation or insulin tolerance test). A blunted CAR with normal or low-normal absolute values is commonly seen in burnout, chronic stress, PTSD, and atypical depression, though the clinical significance remains debated.
Note: The ASP with CAR is a functional assessment of HPA axis dynamics, not a diagnostic test for primary adrenal or pituitary disease. Single abnormal profiles should be confirmed with repeat testing, and suspected pathology (Cushing syndrome, Addison disease) requires additional workup including serum cortisol, ACTH, dynamic suppression or stimulation tests, and imaging. Salivary cortisol assays are method-dependent, and reference ranges are laboratory-specific; results should be interpreted using the performing lab's intervals. The cortisol awakening response is a research-validated biomarker but lacks universal clinical thresholds, and 'optimal' functional ranges are exploratory.
Frequently asked questions
The cortisol awakening response (CAR) is the sharp rise in cortisol that occurs within 30 minutes of waking. It reflects the HPA axis's acute reactive capacity and stress resilience. A blunted CAR has been linked to chronic stress, burnout, and PTSD, whilst an exaggerated response may accompany anxiety and depression.
How to access the ASP/CAR test
The ASP/CAR reference page is free and open to all practitioners. Create a free practitioner account to see pricing, save tests to your list, and generate requisition forms. Verification takes 1–2 business days.
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Published: October 7, 2026
Last reviewed: October 7, 2026
- Clow A, et al. The cortisol awakening response: more than a measure of HPA axis function. Neurosci Biobehav Rev. (2010)
- Pruessner JC, et al. Two formulas for computation of the area under the curve represent measures of total hormone concentration versus time-dependent change. Psychoneuroendocrinology. (2003)
- Chida Y, Steptoe A. Cortisol awakening response and psychosocial factors: a systematic review and meta-analysis. Biol Psychol. (2009)
- Endocrine Society clinical practice guideline: diagnosis of Cushing's syndrome. (2008)
- Nieman LK, et al. The diagnosis of Cushing's syndrome: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. (2008)
This content is for licensed healthcare practitioners only and does not constitute medical advice. Clinical decisions should be based on the full clinical picture and not on any single test result.