Causes
The slowing of the bodys basal metabolic rate associated with hypothyroidism
Pernicious anemia where there is antibody production against parietal cells which normally produce gastric acid. The use of antacids or drugs that decrease gastric acid production (such as H2-receptor antagonists) or transport (such as proton pump inhibitors). A symptom of rare diseases such as mucolipidosis (type IV). A symptom of Helicobacter pylori infection which neutralizes and decreases secretion of gastric acid to aid its survival in the stomach. A symptom of atrophic gastritis or of stomach cancer. Radiation therapy involving the stomach. Gastric bypass procedures such as a duodenal switch and RNY, where the largest acid producing parts of the stomach are either removed, or blinded. VIPomas (vasoactive intestinal peptides) and somatostatinomas are both islet cell tumors of the pancreas. Pellagra, caused by niacin deficiency. Chloride, sodium, potassium, zinc and/or iodine deficiency, as these elements are needed to produce adequate levels of stomach acid (HCl). Sjögrens syndrome, an autoimmune disorder that destroys many of the bodys moisture-producing enzymes
Ménétriers disease, characterized by hyperplasia of mucous cells in the stomach also causing excess protein loss, leading to hypoalbuminemia. Presents with abdominal pain and edema

Risk Factors
Age
It was found that the incidence of achlorhydria in patients under the age of 60 was around 2.3%, whereas it was 5% in patients over the age of 60. In a persons 30s, the prevalence is about 2.5%, and increases to 12% in a persons 80s. An absence of hydrochloric acid increases with advancing age.
Diagnosis
For practical purposes, gastric pH and endoscopy should be done in someone with suspected achlorhydria. Older testing methods using fluid aspiration through a nasogastric tube can be done, but these procedures can cause significant discomfort and are less efficient ways to obtain a diagnosis. A complete 24-hour profile of gastric acid secretion is best obtained during an esophageal pH monitoring study. Achlorhydria may also be documented by measurements of extremely low levels of pepsinogen A (PgA) (< 17 µg/L) in blood serum. The diagnosis may be supported by high serum gastrin levels (> 500–1000 pg/mL).The "Heidelberg test" is an alternative way to measure stomach acid and diagnose hypochlorhydria/achlorhydria. A check can exclude deficiencies in iron, calcium, prothrombin time, vitamin B-12, vitamin D, and thiamine. Complete blood count with indices and peripheral smears can be examined to exclude anemia. Elevation of serum folate is suggestive of small bowel bacterial overgrowth. Bacterial folate can be absorbed into the circulation. Once achlorhydria is confirmed, a hydrogen breath test can check for bacterial overgrowth. Treatment
Treatment focuses on addressing the underlying cause of symptoms. Treatment of gastritis that leads to pernicious anemia consists of parenteral vitamin B-12 injection. Associated immune-mediated conditions (e.g., insulin-dependent diabetes mellitus, autoimmune thyroiditis) should also be treated. However, treatment of these disorders has no known effect in the treatment of achlorhydria.