to 10% of healthy individuals. however, around 85% of pa patients have parietal cell antibodies, which means they are a sensitive marker for the disease. intrinsic factor antibodies are much less sensitive than parietal cell antibodies, but they are much more specific. they are found in about half of pa patients and are very rarely found in other disorders. these antibody tests can distinguish between pa and food-b12 malabsorption. a buildup of certain metabolites occurs in b12 deficiency due to its role in metabolic processes and cellular functions. methylmalonic acid (mma) can be measured in both the blood and urine, whereas homocysteine is only measured in the blood. an increase in both mma and homocysteine distinguishes b12deficiency from folate deficiency because homocysteine alone increases in the latter. elevated gastrin levels can be found in around 80–90% of pa cases, but they may also be found in other forms of gastritis. decreased pepsinogen i levels or a decreased pepsinogen i to pepsinogen ii ratio may also be found, although these findings are less specific to pa and can be found in food-b12 malabsorption and other forms of gastritis. the diagnosis of atrophic gastritis type a should be confirmed by gastroscopy and stepwise biopsy. about 90% of individuals with pa have antibodies for parietal cells; however, only 50% of all individuals in the general population with these antibodies have pernicious anemia. forms of vitamin b12 deficiency other than pa must be considered in the differential diagnosis of megaloblastic anemia. for example, a b12-deficient state which causes megaloblastic anemia and which may be mistaken for classical pa may be caused by infection with the tapeworm diphyllobothrium latum, possibly due to the parasite's competition with host for vitamin b12. the classic test for pa, the schilling test, is no longer widely used, as more efficient methods are available. this historic test consisted, in its first step, of taking an oral dose of radiolabelled vitamin b12, followed by quantitation of the vitamin in the patient's urine over a 24-hour period via measurement of the radioactivity. a second step of the test repeats the regimen and procedure of the first step, with the addition of oral intrinsic factor. a patient with pa presents lower than normal amounts of intrinsic factor; hence, addition of intrinsic factor in the second step results in an increase in vitamin b12 absorption (over the baseline established in the first). the schilling test distinguished pa from other forms of b12 deficiency, specifically, from imerslund–gräsbeck syndrome, a b12-deficiency caused by mutations in cubn that codes for cubilin the cobalamin receptor. treatment hydroxocobalamin injection usp(1000 mcg/ml) is a clear red liquid solution of hydroxocobalamin which is available in a 30-ml brown glass multidose vial packaged in a paper box. shown is 500 mcg b-12 (as 1/2 cc) drawn up in a 0.5-cc u-100 27 gauge x 1/2" insulin syringe, as prepared for subcutaneous injection. pernicious anemia may not be diagnosed at first. more in-depth diagnosis may be required. pernicious anemia caused by a loss of intrinsic factor cannot be prevented. if there are other, reversible causes of low vitamin b12 levels, the cause must be treated. pernicious anemia is usually easily treated by providing the necessary level of vitamin b12 supplementation. severe cases can be treated with intramuscular injections of vitamin b12. less severe cases may be treated with high doses of oral supplemenation of vitamin b12. a nasal spray, gel, and sublingual preparation are also available for people who may have difficulty in swallowing. folate supplementation may affect the course and treatment of pernicious anemia, therefore vitamin b12 replacement is often recommended initially. in some severe cases of anemia, a blood transfusion may be needed to resolve haematological effects. often treatment will be needed for life. prognosis a person with well-treated pa can live a healthy life. failure to diagnose and treat in time, however, may result in permanent neurological damage, excessive fatigue, depression, memory loss, and other complications. in severe cases, the neurological complications of pernicious anemia can lead to death – hence the name, "pernicious", meaning deadly. there is an increased risk of gastric cancer in those with pernicious anemia linked to the common feature of atrophic gastritis. epidemiology pa is estimated to affect 0.1% of the general population and 1.9% of those over 60, accounting for 20–50% of b12 deficiency in adults. a review of literature shows that the prevalence of pa is higher in northern europe, especially in scandinavian countries, and among people of african descent, and that increased awareness of the disease and better diagnostic tools might play a role in apparently higher rates of incidence. history a case of anemia with a first recognition of associated atrophic gastritis a feature of pernicious anemia, was first described in 1824 by james combe. this was fully investigated in 1849, by british physician thomas addison, from which it acquired the common name of addison's anemia. in 1871, the first accurate description of the disease in continental europe was made by michael anton biermer, a german physician who noted the insidious course of the condition. because it was untreatable and fatal at the time, he first referred to it as "pernicious" anemia., russell coined the term subacute combined degeneration of spinal cord. in 1907, richard clarke cabot reported on a series of 1,200 patients with pa; their average survival was between one and three years. pernicious anemia was a fatal disease before about the year 1920; until the importance of the liver in hematopoiesis was recognized, the treatment of pernicious anemia was unsuccessful and arbitrary. it may have motivated george whipple, who had a keen interest in liver diseases, to investigate the liver's role in hematopoiesis. whipple began evaluating the effects of treatments for anemia caused by chronic blood loss. whipple, huber, and robchett studied the effects on hemoglobin and blood regeneration of a variety of treatments, among which only raw liver showed real promise. serendipity is said to have played a role in this discovery. whipple observed that blood regeneration was poor in dogs fed cooked liver after chronic blood loss. had it not been that a lazy laboratory technician gave the dogs raw liver, the much more dramatic response might not have been discovered then. 1930 advert for liver extract to treat pernicious anemia around 1926, george minot and william p. murphy, who learned of whipple's discovery, sought raw liver as a treatment for pernicious anemia. they later suggested a high-protein diet with high amounts of raw liver. this caused a rapid improvement in symptoms and a simultaneous rise in red blood cell counts. fruit and iron were also part of the diet, and it appears that at this point, minot and murphy were not quite sure that the liver was a very important factor. it was thought that iron in liver tissue, not liver juice-soluble factor, cured hemorrhagic anemia in dogs. thus, the discovery of liver juice as a treatment for pernicious anemia had been by coincidence. however, minot, murphy, and whipple received the joint nobel prize for discovering a cure for a previously fatal disease of unknown cause in 1934, becoming the first americans to be awarded the nobel prize in physiology and medicine. it is not easy to eat uncooked liver, and extracts were developed as a concentrate of liver juice for intramuscular injection. in 1928, chemist edwin cohn prepared an extract that was 50 to 100 times stronger than obtained from raw liver. this became part of the standard management of pernicious anemia until the 1950s. the active ingredient in the liver remained unknown until 1948. the anti-pernicious anemia factor was only isolated from the liver by smith, rex, and others. the substance was cobalamin, which the discoverers called "vitamin b12". they showed that giving a few micrograms could prevent relapse in the disease. dorothy hodgkin and co-workers went on to use x-ray crystallography to elucidate the structure of cobalamin for which she, too, was awarded a nobel prize. understanding of the pathogenesis of pernicious anaemia increased over subsequent decades. it had long been known that the disease was associated with defects in the gastrointestinal tract: patients had chronic gastritis and lack of acid secretion (achlorhydria). it is known that transport of physiological amounts of vitamin b12 depends on the combined actions of gastric, ileal and pancreatic components. the gastric moiety was discovered and named 'intrinsic factor' by william castle in 1930. a further important advance was made in the early 1960s by doniach with the recognition that pernicious anemia is an autoimmune disease. pernicious anemia is eventually treated with either injections or large oral doses of b12, typically between 1 and 4 mg daily. a medical author takes the view that mary todd lincoln, the wife of american president abraham lincoln, had pernicious anemia for decades and died from it in 1882. research permeation enhancers treatment using oral drugs is an easier option in management but the bioavailabity of b12 is low. this is due to low absorption in the intestine, and breakdown by enzyme activity. research continues to focus on the use of permeation enhancers or permeation absorbers in combination with the treatment. one of the better performing enhancers studied is salcoprozate sodium (snac). snac is able to form a noncovalent complex with cobalamin while preserving its chemical integrity and protect b12 from gastric acidity. this complex is much more lipophilic than the water-soluble vitamin b12, so is able to pass through cellular membranes with greater ease. molecular dynamics are used in experiments to gain an understanding of the molecular interactions involved in the different molecules used and the degree of ease achieved in absorption across the gastric epithelium.