There are no blood tests or imaging studies specifically for fibromyalgia diagnosis. Fibromyalgia is diagnosed after a thorough history, a complete physical exam, and labs to rule out other diseases.
There are 2 classification criteria developed by the American College of Rheumatology (ACR), that rheumatologist often use to help the diagnosis.
The 1990 ACR criteria established fibromyalgia as “widespread musculoskeletal pain” plus tenderness at 11 or more of the 18 fibromyalgia tender points (see figure). The tender points are mostly either bursae or sites of tendon insertion. Tenderness at 11 or more of the tender points, specially when there is involvement of all 4 quadrants (ie. upper and lower body, right and left sides), is fairly sensitive for fibromyalgia.
The 2010 ACR criteria are significantly more complicated (see table below). According to these criteria, tenderness in specific areas PLUS some of the symptoms are required to be classified as fibromyalgia.
2010 ACR Fibromyalgia diagnostic criteria
Stated more simply, according to this criteria, fibromyalgia diagnosis is made when there is widespread pain (shoulder, upper arm, lower arm, hip, etc) AND there is significant fatigue, waking unrefreshed, cognitive symptoms, and somatic symptoms. Cognitive symtp0ms refer to difficulty with thinking and concentration. Somatic symptoms are what is experienced by the body, including headaches, irritable bowel syndrome, numbness/tingling, dry mouth, painful urination, bladder spasm, to name a few.
It is important to note that other medical conditions may have similar symptoms as fibromyalgia. For example, low thyroid levels can cause fatigue, body aches, and sleep disturbances. Some autoimmune diseases may present with joint and muscle pain, fatigue, and a variety of somatic symptoms. Therefore, before fibromyalgia is diagnosed, it is important that other medical conditions are rule out.
The essentials of fibromyalgia treatment
American College of Rheumatology http://www.rheumatology.org/practice/clinical/patients/diseases_and_conditions/fibromyalgia.asp
Uptodate http://www.uptodate.com/contents/fibromyalgia-beyond-the-basics?source=search_result&search=fibromyalgia+patient&selectedTitle=1%7E150
F Wolfe, DJ Clauw, MA Fitzcharles, DL Goldenberg, RS Katz, P Mease, AS Russell, J Russell, JB Winfield, MB Yunus. The American College of Rheumatology Preliminary Diagnostic Criteria for Fibromyalgia and Measurement of Symptom Severity. Arthritis Care & Research,Vol. 62, No. 5, May 2010, pp 600–610