Narcolepsy can usually be diagnosed by observing how you sleep and ruling out other conditions.
See a GP if you think you have narcolepsy. Before your appointment, you may find it useful to record your symptoms in a diary or complete an Epworth sleepiness questionnaire.
The GP will look closely at your medical and family history. They'll ask about your sleeping habits and any other symptoms you have.
Narcolepsy can be difficult to diagnose because the symptoms can be similar to those of other conditions, such as:
Excessive daytime sleepiness can also sometimes be caused by the side effects of certain medicines.
Your GP may carry out several tests to help rule out other conditions that could be causing your symptoms.
For example, you may have a physical examination, blood pressure tests and blood tests.
If your GP thinks you may have narcolepsy, they'll refer you to a specialist in sleep disorders, who will analyse your sleep patterns.
There are many different ways your sleep can be analysed.
The Epworth sleepiness scale (PDF, 64kb) is a questionnaire used to assess how likely it is you'll fall asleep while doing different activities.
Your GP will use the results to decide whether to refer you to a sleep specialist.
When filling out the questionnaire, you'll be asked to rank the likelihood that you'll fall asleep in situations such as sitting and reading, watching television and travelling as a passenger in a car.
A score of 10 or below means you have the same level of daytime sleepiness as the general population. If you score 11 or above, you have an increased level of daytime sleepiness.
If this is the case, your GP will probably refer you to a sleep specialist for further investigation.
Polysomnography is an investigation of your sleep carried out at a specialist sleep centre.
It usually involves staying overnight at the sleep centre so your sleeping patterns can be analysed.
During the night, several different parts of your body will be monitored using electrodes and bands that are placed on your body while you sleep.
Sensors will also be placed on your legs and an oxygen sensor will be attached to your finger.
A number of different tests will be carried out during polysomnography, including:
Sound recording and video equipment may also be used to record sound and images.
After you have slept, a specialist will analyse your test results to determine whether you have normal brain wave activity, breathing patterns, and muscle and eye movement.
A multiple sleep latency test measures how long it takes for you to fall asleep during the day. You may have this test after polysomnography.
You'll be asked to take several naps throughout the day, and a specialist will analyse how quickly and easily you fall asleep.
If you have narcolepsy, you'll usually fall asleep easily and enter rapid eye movement (REM) sleep very quickly.
You may also have a blood test to find out whether you have a genetic marker known as HLA DQB * 0602, which is associated with narcolepsy.
A positive result supports a diagnosis, but does not make it 100% certain – 30% of people without narcolepsy also have the genetic marker.
Narcolepsy is often linked to a deficiency in the sleep-regulating brain chemical hypocretin, also known as orexin.
Research has shown that measuring the level of hypocretin in your cerebrospinal fluid, which surrounds the brain and spinal cord, can be useful in diagnosing narcolepsy.
To measure your level of hypocretin, a sample of cerebrospinal fluid is removed using a needle during a procedure called a lumbar puncture.
This test is increasingly being used by sleep disorder specialists to help make a diagnosis.