Is there a lab test available to measure melatonin levels?

Laboratory Testing for Melatonin Levels

Yes, laboratory tests are available to measure melatonin levels through three validated methods: plasma (blood), saliva, and urine collection for the metabolite 6-sulphatoxymelatonin. 1, 2

Available Testing Methods

Saliva Testing (Recommended for Clinical Use)

Saliva testing is the most practical option for routine clinical assessment of melatonin levels. 1

• Salivary melatonin can be measured using radioimmunoassay (RIA) or ELISA techniques 3, 2
• The dim-light melatonin onset (DLMO) threshold for saliva is typically 3-4 pg/mL 1, 4, 5
• Saliva levels are approximately 30% of plasma levels (about 3 times lower) 1
• Saliva reflects the free (unbound) hormone concentration, which is the biologically active fraction 6
• Collection is non-invasive and can be performed at home without medical personnel 1

Common pitfall: Viscous saliva samples may be difficult to process through extraction columns, but dithiothreitol treatment can resolve this issue without altering melatonin values 7

Plasma Testing (Research Standard)

Plasma melatonin provides the highest resolution and sensitivity but is not recommended for routine clinical use. 1

• Plasma DLMO threshold is approximately 10 pg/mL 1, 5
• Requires intravenous catheter placement at least 2 hours before sampling to avoid adrenergic effects on melatonin levels 1
• Optimal sampling involves frequent intervals (every 20-30 minutes) throughout the night 1
• Provides the most informative data on circadian phase, duration, and amplitude when collected over 24 hours 1

Major limitations: Invasive procedure, requires trained medical personnel, risk of catheter complications, and potential sleep disruption 1

Urine Testing

Urine collection measures the primary melatonin metabolite 6-sulphatoxymelatonin (aMT6s). 1, 2

• Samples are typically collected in 2-hour bins under dim light conditions 1
• Peak levels occur between 04:00 and 08:00 hours 1
• Less sensitive than plasma or saliva for determining precise circadian phase timing 1

Critical Testing Conditions

Lighting Requirements

All melatonin testing must be performed under dim light conditions (<10 lux) to avoid suppression of melatonin secretion. 4

• Even room-level illumination can suppress melatonin and invalidate results 4
• This is why the test is called "dim-light melatonin onset" (DLMO) 1, 4

Timing Considerations

Sample collection timing is crucial because melatonin has a clear circadian rhythm with low daytime levels (<1 pg/mL in plasma) and nighttime peaks. 3, 2

• In individuals with normal circadian phase, DLMO occurs approximately 2-3 hours before habitual sleep onset 1, 4
• Melatonin begins rising 1-3 hours before habitual bedtime 4

Medication Interference

Several medications can suppress melatonin levels and must be considered when interpreting results: 4, 8

• NSAIDs should be avoided for 72 hours before testing 4, 8
• Beta-blockers suppress endogenous melatonin production 8
• Alcohol can suppress melatonin levels 4

Other Confounding Factors

• Postural changes and exercise can increase melatonin levels 4
• Absence of detectable melatonin may indicate either low synthesis or abnormal circadian phase (melatonin production at an unexpected time) 1, 4

Assay Quality Considerations

Modern commercial assays using RIA or ELISA are available, but not all achieve the accuracy standards set by mass spectrometry assays (daytime plasma levels <1 pg/mL). 3

• Validation of the specific assay being used is essential 3
• Early radioimmunoassays provided accurate nocturnal levels but often produced inaccurate basal (daytime) measurements 3
• Mass spectrometry assays provide the gold standard target values 3