Depression and other psychological conditions can produce fatigue, so people who report fatigue are routinely screened for these conditions, along with substance use disorders, poor diet, and lack of physical exercise, which paradoxically increases fatigue. Basic medical tests may be performed to rule out common causes of fatigue. These include blood tests to check for infection or anemia, a urinalysis to look for signs of liver disease or diabetes mellitus, and other tests to check for kidney and liver function, such as a comprehensive metabolic panel. Other tests may be chosen depending on the patients social history, such as an HIV test or pregnancy test. Comparison with sleepiness
Fatigue is generally considered a more long-term condition than sleepiness (somnolence). Although sleepiness can be a symptom of a medical condition, it usually results from lack of restful sleep, or a lack of stimulation. Chronic fatigue, on the other hand, is a symptom of a greater medical problem in most cases. It manifests in mental or physical weariness and inability to complete tasks at normal performance. Both are often used interchangeably and even categorized under the description of being tired. Fatigue is often described as an uncomfortable tiredness, whereas sleepiness is comfortable and inviting. Measurement
Fatigue can be quantitatively measured. Devices to measure medical fatigue have been developed by Japanese companies, among them Nintendo (cancelled). Nevertheless, such devices are not in common use outside Japan.
Chronic fatigue may refer to:

Fatigue (medical)#Chronic, a long-term state of physical or mental exhaustion, a symptom of many chronic illnesses
Chronic fatigue syndrome, a medical condition characterized by long-term fatigue and other long term symptoms that limit a persons ability to carry out ordinary daily activities.