To diagnose carpal tunnel syndrome (CTS), the physician will review the patient’s medical history and perform a physical examination. In learning about the medical history, the physician will ask about any conditions that may be associated with CTS, such as pregnancy, diabetes, hypothyroidism or rheumatoid arthritis.

The physician will also inquire about any recent accidents or injuries involving the wrist, hand or arm that may be causing CTS. In addition, the physician will ask about any activities the patient engages in that might contribute to CTS, such as typing, playing a musical instrument or using power tools.

During the physical exam, the physician will test the feeling in the fingers and the strength of the muscles in the hand because these can be affected by CTS. The physician will also examine the neck, shoulder and elbow also to determine the possible level of nerve entrapment. In many patients, applied pressure on the median nerve in the wrist – by either bending the wrist (Phalen's sign), tapping on the nerve (Tinel's sign) or just pressing on it – can bring about the symptoms.

To confirm a diagnosis of CTS, a physician may order further tests, which may include:

• Blood tests. Laboratory analysis of blood samples to determine if any underlying condition is contributing to the symptoms. In some cases, treatment of the underlying disorder alleviates CTS symptoms. In the case of pregnancy, CTS usually disappears after childbirth.
  
  
• Ultrasound. A noninvasive imaging test that uses sound waves to produce images of the shape and outline of various tissues and organs in the body. Ultrasound can show impaired movement of the median nerve.
  
  
• X-rays. Type of radiography using low doses of radiation to produce images of body parts on film or fluorescent screens. However, x-rays are useful only when injuries such as a fracture in the hand or wrist are present.
  
  

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• MRI (magnetic resonance imaging). A noninvasive or minimally invasive imaging test that uses powerful magnets to produce images of organs and vessels in the body on a computer screen and film. An MRI can allow the physician to view the anatomy of the wrist but by itself is not very useful in diagnosing CTS.

• Electrodiagnostic tests. These tests may be useful in localizing impingement of the median nerve:
  
• • Nerve conduction study. Two electrodes are taped to the hand and wrists. A small shock is passed through the median nerve to see if electrical impulses are slowed in the carpal tunnel. However, this type of test is not always definitive because a false-negative result can occur in up to 10 percent of patients.
    
    
  • Electromyography. A physician inserts a thin-needle electrode into the muscle being studied. An instrument records the electrical activity in the muscle at rest and as the patient contracts or moves it. The electrical activity is viewed on a screen and allows the physician to determine the severity of damage to the median nerve.

Electromyography can be painful and is usually recommended in certain instances (e.g. conservative therapy was unsuccessful, unclear diagnosis, evidence of motor dysfunction). However, this test is one of the best diagnostic tests and is positive in more than 85 percent of the patients with the disease. In cases where surgery is needed, many surgeons may for legal reasons require this type of electrodiagnostic proof of nerve compression before performing surgery.

Researchers in 2007 reported finding biomarkers (chemicals in the body) that may be an early signal of CTS. The discovery could one day lead to a test that allows improved diagnosis and prevention of the condition.