A 40-year-old woman in China arrived for a routine upper gastrointestinal examination carrying a medical file that already listed three serious autoimmune conditions. Her immune system had attacked her liver, her bile ducts, and her large intestine. But her blood tests pointed to something that didn’t fit the known picture: severe iron deficiency, without any apparent source of bleeding. Doctors ran repeated stool tests and ordered a gynecological examination. No blood loss could be found. That meant the iron wasn’t disappearing – it was never being absorbed in the first place.
The explanation was a fourth autoimmune disease, quietly destroying the stomach’s ability to process iron from food. The case, published in August 2026 in Frontiers in Immunology, a peer-reviewed journal, raises a question that clinicians increasingly have to reckon with: when one autoimmune disease is confirmed, how hard should doctors look for the next one?
Autoimmune polyglandular syndromes are characterized by associations of two or more autoimmune diseases in the same individual. This patient had four simultaneously confirmed, each targeting a different part of her digestive system. The treating physicians debated whether the combination met the criteria for a known syndrome and ultimately concluded it came close, but not quite.
The four diseases, explained
The confirmed conditions in this patient included ulcerative colitis, autoimmune hepatitis, primary sclerosing cholangitis, and autoimmune gastritis – the fourth disease identified through endoscopic, histological, and serological testing.
Multiple autoimmune syndrome, or MAS, is defined as three or more autoimmune disorders occurring in the same individual.
Ulcerative colitis had been the first confirmed diagnosis. Ulcerative colitis is a chronic inflammatory bowel disease in which immune reactions inflame the lining of the large intestine, causing pain, diarrhea, and bleeding. At the time of her gastric examination, the condition was in remission – a clinically significant detail that made intestinal bleeding an unlikely cause of her iron deficiency and pushed doctors to look elsewhere.
Autoimmune hepatitis was her second confirmed condition. Autoimmune hepatitis occurs when the immune system mistakenly attacks and inflames the liver, causing chronic inflammation and damage.
Primary sclerosing cholangitis (PSC) was the third. PSC is a chronic, progressive disease of the bile duct system that scars and narrows the ducts carrying bile from the liver to the small intestine – bile being the fluid that helps the body digest fats. A well-documented association exists between PSC and inflammatory bowel disease: 60–80% of people with PSC have IBD, particularly ulcerative colitis.
Autoimmune gastritis was the fourth and final confirmed disease – the one doctors hadn’t initially suspected. When they examined the stomach lining, they found it severely thinned. Under a microscope, immune cells were actively inflaming the tissue. Many of the cells that normally produce stomach acid – called parietal cells – were damaged or absent. Blood tests also detected antibodies directed specifically against these acid-producing cells, confirming the diagnosis.
Why the stomach matters for iron absorption
Stomach acid does more than break down food. It also prepares dietary iron for absorption in the small intestine. When autoimmune gastritis destroys the parietal cells that produce that acid, iron from food becomes harder to absorb – even when a person’s diet contains adequate amounts of iron. This is why the woman’s iron levels were critically low despite no identifiable blood loss.
Her hemoglobin, the protein in red blood cells that carries oxygen, had fallen to 89 g/L. Mayo Clinic lists the normal range for women as 11.6 to 15.0 g/dL, or 116 to 150 g/L. Her level was therefore well below the normal range.
The treating physicians prescribed iron supplementation and scheduled a repeat stomach examination with biopsies within one to two years, given that autoimmune gastritis is associated with long-term risks that require endoscopic surveillance.
The patient’s vitamin B12 level was still normal at the time of the examination. Iron deficiency is commonly found in patients with autoimmune gastritis and typically precedes vitamin B12 deficiency, which tends to emerge later as stomach damage progresses. The physicians planned to monitor her B12 and folate levels going forward.
The diagnostic puzzle: was this a named syndrome?
The cluster of diseases in this patient closely resembled a recognized condition called autoimmune polyglandular syndrome type 3B, or APS-3B. APS-3B specifically involves gastrointestinal autoimmune diseases occurring alongside autoimmune thyroid disease.
The woman did have hypothyroidism – insufficient thyroid hormone – but her thyroid had been surgically removed because of thyroid cancer. Hypothyroidism following a total thyroidectomy is an expected medical consequence, not evidence of an immune attack on the gland. Because doctors lacked the serological or tissue evidence to confirm that her immune system had also targeted her thyroid, the case resembled APS-3B but could not be formally classified as it.
In prior published cases, recognizing APS-3B has helped physicians diagnose autoimmune gastritis, a condition that is challenging to identify based on endoscopic findings alone. The 2026 Frontiers in Immunology case reinforces that clinical logic: when gastrointestinal autoimmune diseases cluster in a single patient, the stomach deserves explicit investigation, even when it isn’t the presenting complaint.
If a patient’s unexplained anemia prompts stomach testing only after other causes are ruled out – rather than as part of a proactive screen for additional autoimmune conditions – there can be a significant diagnostic delay.
Who is most vulnerable to multiple autoimmune diseases?
The gender disparity in autoimmune disease is well-documented. Data from the NIH Office of Research on Women’s Health shows that about 80% of people with autoimmune diseases are women.
Genetics play a central role in who develops multiple autoimmune diseases. A study published in BMC Medicine found that affected individuals tend to cluster in families, with shared susceptibility genes contributing to the co-occurrence of multiple autoimmune diseases within a single person or across family members.
Read more: 8 autoimmune symptoms you could be overlooking
Overlapping symptoms can delay diagnosis and complicate treatment when people have multiple autoimmune diseases affecting different organs. A symptom like fatigue, for instance, could plausibly stem from anemia, liver disease, or hypothyroidism – all at once, in a patient like this one.
What this means for you
The 40-year-old woman’s case is a single report, and the authors in Frontiers in Immunology are explicit about its limits: it cannot establish how common this specific combination of diseases is, whether one condition caused another, or whether everyone with multiple autoimmune diagnoses should automatically undergo stomach testing.
What the case does establish is a concrete clinical signal. Unexplained iron deficiency in a patient with pre-existing autoimmune disease – particularly one involving the gastrointestinal tract – should trigger investigation of the stomach’s acid-producing function, not just a search for bleeding. The two mechanisms of iron depletion are different, and the standard workup for one does not rule out the other.
For patients managing one or more autoimmune conditions, a few actions follow directly from this report and the broader research on autoimmune clustering. If your iron levels are persistently low despite supplementation or adequate dietary intake, and your doctor has already ruled out blood loss, ask about anti-parietal cell antibody testing – the blood test that flags autoimmune gastritis before symptoms become obvious. Care coordinated across all active autoimmune conditions, rather than managed in isolation, is also likely to catch new developments earlier.
Autoimmune gastritis carries a risk of developing specific stomach changes that require long-term endoscopic surveillance in patients with confirmed disease. If you have been diagnosed with autoimmune gastritis, ask your gastroenterologist about a surveillance schedule. Early detection of precancerous changes in the stomach lining is far more treatable than late-stage disease.
The fourth disease in this patient was found not because she had dramatic new symptoms, but because doctors looked beyond the already-confirmed diagnoses. Persistent, unexplained lab abnormalities in a patient with known autoimmune disease deserve the same scrutiny as new symptoms.
Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.
AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.