Chronic Endometritis: Understanding Your Pathology Report

Section Editor: Kianoosh Keyhanian MD FRCPC
August 31, 2026

Chronic endometritis is long-lasting inflammation of the endometrium, the inner lining of the uterus. Inflammation is the immune system’s response to infection or injury. Acute inflammation starts suddenly and resolves quickly. Chronic inflammation builds gradually and can persist for months.

This diagnosis is distinctive because it is defined by a single cell type. Pathologists diagnose chronic endometritis when they find plasma cells, a kind of immune cell, in the lining of the uterus. Plasma cells are not normally found there, so their presence signals ongoing inflammation.

Chronic endometritis is not cancer, and it is not precancerous. Many people who have it feel entirely well. Its importance lies in its link with difficulty becoming pregnant and with repeated miscarriage, which is why it is most often looked for in a fertility setting. This article will help you understand what this diagnosis means on your pathology report, what each term means, and why it matters for your care.

What causes chronic endometritis?

Chronic endometritis is often related to a low-grade infection in the uterus, though a specific organism is identified in only a minority of cases. Recognized causes and associations include:

Ordinary bacteria — Organisms such as Escherichia coli, Enterococcus, Streptococcus, and Gardnerella are the ones most often found. These are common bacteria rather than sexually transmitted ones.
Sexually transmitted infections — Chlamydia and gonorrhea can both cause it, though they account for a minority of cases.
Tuberculosis — An uncommon cause in North America, but an important one in parts of the world where tuberculosis is widespread.
Procedures involving the uterus — A dilation and curettage, hysteroscopy, or other instrumentation can be followed by chronic endometritis.
An intrauterine device — An IUD is a recognized association. This does not mean the device must be removed, and that decision is made with your doctor.
Retained pregnancy tissue — Tissue remaining after a miscarriage or delivery is a well-recognized trigger.
Growths in the uterus — Endometrial polyps and fibroids that project into the cavity are both associated with plasma cells in the surrounding lining.

In many cases,s no cause is identified. This does not mean the finding is wrong or that treatment will not work.

What are the symptoms?

Many people with chronic endometritis have no symptoms at all, and the condition is found only when the lining of the uterus is examined for another reason. When symptoms do occur, they may include:

Abnormal bleeding — Heavy periods, bleeding between periods, or spotting.
Pelvic pain or discomfort — Often mild and ongoing rather than severe.
Unusual vaginal discharge — Sometimes present, sometimes not.
Pain during intercourse — Reported by some people with this diagnosis.
Difficulty becoming pregnant or repeated miscarriage — Often the reason the biopsy was done in the first place, rather than a symptom noticed on its own.

None of these symptoms are specific to chronic endometritis, and each can have other causes.

How is the diagnosis made?

Chronic endometritis is diagnosed on an endometrial biopsy, a small sample of the lining of the uterus taken in a clinic using a thin flexible tube. The procedure takes a few minutes and usually does not require anesthesia. A sample may also be obtained during a hysteroscopy, where a camera is passed into the uterus, or from tissue removed during another procedure.

The timing of the biopsy matters. Plasma cells are normally present in the lining around the time of a period, and while it is breaking down, so a sample taken then is difficult to interpret. Biopsies are usually taken in the first half of the cycle, after bleeding has stopped, so that any plasma cells found are meaningful.

A pathologist examines the tissue for plasma cells and for the other changes described below. Because plasma cells can be difficult to identify with certainty, a special stain is usually added, as described in the immunohistochemistry section. Bacterial cultures or molecular tests for specific organisms are sometimes done as well, though these often come back negative even when the microscopic findings are clear.

What does chronic endometritis look like under the microscope?

Chronic endometritis is inflammation of the uterine lining, identified by plasma cells within the supporting tissue. Under the microscope, the pathologist looks for the following features.

Plasma cells — The finding the diagnosis rests on. Plasma cells are immune cells that make antibodies. They have a distinctive appearance, with the nucleus pushed to one side of the cell, but they can be hard to pick out among the other cells of the endometrium.
Other immune cells — Lymphocytes and similar cells are often present. On their own, these do not establish the diagnosis, because small numbers of lymphocytes are normal in the endometrium.
Swollen, dense supporting tissue — The tissue between the glands may look edematous, meaning swollen with fluid, or unusually cellular.
Irregular glands — The glands of the endometrium may look distorted, or out of step with the phase of the cycle.
Surface changes — The lining may show reactive changes and small areas of breakdown.
Scarring — Long-standing inflammation can leave fibrosis, or scar tissue, in the lining.

Immunohistochemistry

Immunohistochemistry is a laboratory test that uses antibodies to detect specific proteins inside cells. For chronic endometritis, one stain does nearly all the work.

CD138. Positive in plasma cells. CD138, also called syndecan-1, is a protein on the surface of plasma cells. The stain colors them so they stand out clearly from the surrounding tissue.

This stain matters more here than in most diagnoses. Plasma cells are difficult to identify on a routine slide. Studies comparing the two approaches have found that adding CD138 improves diagnostic accuracy. It also improves agreement among pathologists reviewing the same slide. If your report mentions a CD138 stain, it was performed to find or confirm plasma cells.

The stain is not perfectly specific. CD138 also marks the surface lining cells of the endometrium, so the pathologist counts only stained cells within the supporting tissue between the glands. This is one reason the interpretation requires care.

Why do laboratories sometimes disagree about this diagnosis?

This matters if you have had biopsies reported differently, or if a second opinion reached a different conclusion. Chronic endometritis has no agreed international definition, and the disagreement is about numbers.

Everyone accepts that plasma cells in the endometrium define the condition. What remains unsettled is how many are required. Published criteria range from a single plasma cell in ten high-power fields at one end to five or more in a single high-power field at the other. That is roughly a fiftyfold difference. A biopsy called positive using one threshold may be called negative using another, without either pathologist making an error.

Two other factors add variation. Plasma cells are not evenly spread through the lining so that a small biopsy may miss them. And a sample taken at the wrong point in the cycle can show plasma cells that are a normal part of menstruation rather than a sign of disease.

None of this means the diagnosis is unreliable, but it does mean the finding is best interpreted alongside your clinical situation rather than on its own. If you have conflicting results, ask whether the same threshold and stain were used.

Why does chronic endometritis matter?

Chronic endometritis is looked for mainly because of its association with reproductive problems. Ongoing inflammation appears to interfere with an embryo settling into the lining of the uterus. The condition is found more often in people with repeated failure of embryo transfer during IVF, and in people with recurrent pregnancy loss, than in the general population.

The honest position on the evidence is that the association is well documented, but the benefit of treatment remains unsettled. Several studies report better pregnancy outcomes after antibiotic treatment, while others find no clear difference, and varying diagnostic thresholds make the studies difficult to compare. Fertility specialists differ in how much weight they place on this diagnosis, and that is a reasonable difference of opinion rather than a sign that someone is wrong.

Outside a fertility context, chronic endometritis found incidentally in a biopsy taken for bleeding is usually a minor finding, treated if symptoms warrant it and otherwise not pursued.

How is chronic endometritis treated?

Treatment is a course of antibiotics. Doxycycline is the usual first choice, typically taken for two weeks. If plasma cells persist afterward, clinicians generally try a different antibiotic combination next. Most cases clear after one or two courses.

In a fertility setting, a repeat biopsy is often done after treatment to confirm the plasma cells have gone before proceeding with embryo transfer. Outside that setting, a repeat biopsy is not usually needed. If a polyp, fibroid, retained pregnancy tissue, or another underlying cause is identified, treating it is generally more effective than antibiotics alone.

What other findings may be described in the report?

Chronic endometritis is often reported alongside other findings in the same biopsy. Findings commonly described include:

The phase of the cycle — The report usually states whether the lining is proliferative or secretory, which reflects where you were in your cycle when the sample was taken.
Endometrial polyp — A benign growth of the lining, and a common accompaniment to chronic endometritis.
Breakdown and bleeding — Changes reflecting a lining that is shedding, which may be the reason for abnormal bleeding.
Retained pregnancy tissue — If products of conception are present, this may be both the cause of the inflammation and the reason for the procedure.
Hyperplasia or atypical changes — If the lining shows crowded glands, the report will say so and name the finding, such as endometrial hyperplasia. These are reported and managed separately from the inflammation.

Questions to ask your doctor

Was a CD138 stain used to make this diagnosis?
How many plasma cells were found, and what threshold did the laboratory use?
When in my cycle was the biopsy taken?
Was a specific infection identified?
Was anything else found in the biopsy, such as a polyp or retained tissue?
Which antibiotic do you recommend, and for how long?
Will I need a repeat biopsy after treatment?
Should my partner be tested or treated?
Could this explain my difficulty becoming pregnant, or my miscarriages?
How much weight do you place on this diagnosis in my situation?
Do I need to have my IUD removed?
What symptoms should prompt me to contact you?