Dyspepsia is a symptom or a combination of symptoms that alerts a clinician to the presence of an upper GI (UGI) problem. Typical symptoms include epigastric pain or burning, early satiety and postprandial fullness, belching, bloating, nausea, or discomfort in the upper abdomen. Symptoms are the central focus of this assessment; it is therefore essential that they are described in a manner that is relevant to patients. 
The nomenclature for dyspepsia is confusing. This is largely because some medical organizations include all UGI symptoms in the term dyspepsia, then separate patients with symptoms suggesting gastroesophageal reflux disease (GERD) for appropriate management, whereas others recognize the overlap in symptoms between the various causes of UGI symptoms but choose to separate the symptoms suggesting GERD before applying the term dyspepsia. Both approaches recommend identifying patients whose symptoms suggest GERD and managing them as having reflux disease.
The Canadian Dyspepsia Working Group (CANDYS)  and the UK National Institute for Health and Clinical Excellence (NICE)  include GERD symptoms in the term dyspepsia. CANDYS does not require a specific duration for symptoms, whereas NICE requires 4 weeks and ROME III  requires 12 weeks in the last year to qualify as dyspepsia. The American Gastroenterological Association's (AGA) technical review for the evaluation of dyspepsia  excludes patients with symptoms that suggest GERD and includes only the typical symptoms listed above.
Patients with dyspepsia can be classified based on the type or outcomes of the investigations they have received. Research papers will often refer to different categories of dyspepsia patients, so it is important to understand the descriptions of the most common subgroups of dyspepsia patients that have been described.
Uninvestigated dyspepsia is classified as a condition with characteristic symptoms clinically assessed to be originating in the upper GI (UGI) tract, but which has not been recently investigated by UGI endoscopy.    Symptoms include epigastric pain or burning, early satiety and postprandial fullness, belching, bloating, nausea, or discomfort in the upper abdomen.
Functional dyspepsia (sometimes called nonulcer dyspepsia) refers to a situation where UGI endoscopy did not reveal a potential cause for the dyspepsia. It is generally reserved for patients with a normal endoscopy whose symptoms do not suggest GERD. (GERD patients with normal endoscopy are said to have nonerosive reflux disease or NERD.)    
GERD and dyspepsia are related. Patients with troublesome heartburn and/or acid regurgitation can be diagnosed clinically as having GERD.  It is known that many patients with GERD will have atypical presentations such as epigastric burning or pain, and therefore their symptoms will cause them to be placed into the group of uninvestigated dyspepsia patients. More than half of GERD patients have a normal esophagus at endoscopy. The difficulty separating GERD from other UGI disorders based on either symptoms or endoscopic findings has led some groups (CANDYS and NICE ) to include GERD in the broad group of patients with dyspepsia. This categorization would include patients with all UGI symptoms under the term uninvestigated dyspepsia. Other groups (AGA ) prefer to separate UGI symptoms into the two broad categories, GERD and dyspepsia, based on symptom classification. With either categorization there is now widespread agreement that patients with troublesome heartburn and/or acid regurgitation can generally be diagnosed clinically as having GERD, without the need for endoscopy. 
The extent or severity of the patient's dyspepsia is measured by the patient's report of the impact of symptoms on quality of life and function. The patient's assessment of the severity of dyspepsia usually relates to the degree to which it affects work, sleep, diet, or leisure.  
Although most people affected by dyspepsia do not seek medical care for their symptoms, roughly one quarter of the population of the developed world suffers from dyspepsia annually. Rates range from 13% to 40% in different countries.  The condition is one of the most common diagnoses in primary care practices.  Dyspepsia remains a common and important diagnosis even into the geriatric age group.  Follow-up of patients over 5 to 7 years shows a benign but recurrent nature of the disease in 50% of cases.  1[A] Evidence Evidence There is evidence of special issues relating to dyspepsia in women, particularly in relation to impact on quality of life and history of abuse.  Dyspepsia has been shown to have a significant negative impact on quality of life. The impact relates to changes in sleep, diet, and interference with work and leisure activities. Women who have experienced abuse appear to be particularly vulnerable to developing dyspepsia symptoms. Work is being done to improve our understanding of brain-to-gut connections that appear to be involved in this association. This work may help shed light on the association between dyspepsia and irritable bowel syndrome (IBS) that is a recurring theme in recent articles.