PCOS and endometriosis are diagnosed through very different processes. PCOS is typically confirmed with blood tests and an ultrasound, while endometriosis often requires surgery for a definitive answer. If you suspect you have one or both conditions, understanding what each diagnostic path looks like can help you prepare for appointments and advocate for the right tests.
These two conditions can also coexist. In a study of women undergoing gynecologic surgery, about 1 in 20 had both PCOS and endometriosis. In the general population, the overlap was closer to 1 in 50. Because symptoms can blur together, getting clarity on which condition you’re dealing with matters for choosing the right treatment.
How PCOS Is Diagnosed
PCOS is a clinical diagnosis based on the Rotterdam criteria. You need to meet at least two of three criteria: irregular or absent ovulation, signs of excess androgens (male-pattern hormones), and polycystic-appearing ovaries on ultrasound. There’s no single test that confirms PCOS on its own. Instead, your provider pieces together blood work, imaging, and your menstrual history to build the picture.
Importantly, PCOS is also a diagnosis of exclusion. Before confirming it, your provider needs to rule out other conditions that cause similar symptoms, including thyroid disorders, high prolactin levels, adrenal gland problems, and in rare cases, androgen-secreting tumors. This is why the testing panel for PCOS often feels broader than you’d expect.
Blood Tests for PCOS
The core blood test measures testosterone. Total testosterone is generally more reliable than free testosterone because the lab methods for measuring free testosterone can be inconsistent. Most women with PCOS have testosterone levels at or below 150 ng/dL. If levels reach 200 ng/dL or higher, that raises concern for a tumor rather than PCOS, and your provider will investigate further.
Your provider will also likely check your ratio of luteinizing hormone (LH) to follicle-stimulating hormone (FSH). A ratio of 2:1 or higher is suggestive of PCOS, though it’s not definitive on its own. Thyroid hormones and prolactin levels are typically checked at the same time to rule out conditions that mimic PCOS symptoms.
Timing matters for these blood draws. If you’re still having periods, the sample should be taken on days 1 through 5 of your cycle (during or just after your period starts). Testosterone production roughly doubles later in the cycle, which can push results above normal ranges and lead to a misleading result. If you’re not getting periods at all, the blood draw can happen any time.
If you’ve been on hormonal birth control, be aware that it lowers testosterone and affects LH and FSH levels. Ideally, you’d be off oral contraceptives for about three months before testing to get accurate baseline values.
Ultrasound for Polycystic Ovaries
A transvaginal ultrasound looks for polycystic ovarian morphology, defined as 20 or more follicles or an ovarian volume of 10 mL or greater in at least one ovary. If a transvaginal scan isn’t possible, a transabdominal ultrasound uses a lower threshold of 10 or more follicles or the same 10 mL volume cutoff.
Keep in mind that having polycystic-appearing ovaries alone doesn’t mean you have PCOS. Many women have this ultrasound finding without the condition. It only becomes part of the diagnosis when combined with at least one of the other two criteria.
How Endometriosis Is Diagnosed
Endometriosis is harder to pin down. Unlike PCOS, there’s no blood test or simple imaging study that reliably confirms it. The preliminary diagnosis usually starts with your clinical history, because most women with endometriosis have completely normal results on physical examination.
Symptom Patterns That Point to Endometriosis
Certain pain patterns strongly suggest endometriosis and help your provider decide whether to pursue more advanced testing. The hallmark symptoms include painful periods that don’t respond well to standard pain relievers or birth control pills, pain during intercourse, pain with bowel movements, pain during urination, and bleeding between periods. Many women also present with unexplained infertility as their primary concern, sometimes without significant pain.
Tracking your symptoms in detail before your appointment is one of the most useful things you can do. Note when pain occurs in relation to your cycle, where exactly you feel it, and how severe it is. This information helps your provider determine whether imaging or surgical evaluation is warranted.
Imaging Options
Ultrasound can sometimes detect endometriomas (cysts on the ovaries caused by endometriosis), but it misses most other forms of the disease. MRI is better at identifying deep infiltrating endometriosis, the type that grows into the walls of organs like the bowel or bladder. In studies, MRI detected deep infiltrating endometriosis with about 67% sensitivity and 85% specificity. That means it catches roughly two-thirds of cases and correctly rules it out in most women who don’t have it.
Those numbers are useful but imperfect. A normal MRI does not rule out endometriosis, especially superficial lesions scattered across the pelvic lining. Imaging works best for identifying larger, deeper deposits and is most helpful when your provider is planning surgery and needs to know what they’re likely to find.
Laparoscopy: The Definitive Test
The gold standard for confirming endometriosis is laparoscopy with biopsy. This is a minimally invasive surgery where a small camera is inserted through a tiny incision near your navel. The surgeon visually inspects the pelvic cavity under magnification, looking for characteristic lesions: dark blue or black spots on the pelvic lining, red flame-like patches, white scarred areas, or adhesions where organs have become stuck together.
Visual identification alone isn’t enough for a certain diagnosis. Endometriosis has a wide range of appearances, and some lesions look like endometriosis but aren’t, while others don’t look suspicious but are. Surgeons take tissue samples using punch biopsy forceps, and a pathologist examines them under a microscope for specific markers: endometrial glands, surrounding tissue called stroma, fibrosis, and iron-laden immune cells that indicate old bleeding. This histological confirmation is considered the true first step in a reliable diagnosis.
Without tissue confirmation, there’s a real risk of misdiagnosis in either direction. A visual-only diagnosis can lead to unnecessary or prolonged treatment, or it can miss disease entirely. If you’re told you have endometriosis based on surgery, it’s reasonable to ask whether biopsies were taken and confirmed by pathology.
Testing for Both Conditions at Once
If you have symptoms that overlap, such as irregular periods, pelvic pain, and difficulty conceiving, your provider can begin evaluating for both conditions simultaneously. The PCOS workup (blood tests and ultrasound) is noninvasive and can be done early. Endometriosis evaluation typically starts with a detailed symptom history and imaging, with laparoscopy reserved for cases where the clinical picture is strong enough to justify surgery.
One practical consideration: if you’re being evaluated for PCOS and your testosterone comes back normal, your periods are somewhat regular, and your ultrasound doesn’t show polycystic morphology, but you’re still experiencing significant pelvic pain, that’s a signal to shift focus toward endometriosis. The reverse is also true. Persistent irregular cycles and signs of excess androgens in someone being worked up for pelvic pain should prompt PCOS screening alongside the endometriosis evaluation.
Non-Invasive Endometriosis Tests
You may have seen headlines about blood or saliva tests for endometriosis. Researchers have investigated protein markers like BCL6 and SIRT1 in blood, urine, and cervical samples, but the results so far have been disappointing. One study found no significant differences in these markers across bodily fluids that would make them useful as a standalone diagnostic tool. The markers show more promise when measured directly in endometrial tissue biopsies, but that still requires a procedure.
For now, there is no validated blood test or at-home kit that can reliably diagnose endometriosis. If a company markets one, treat the claim with skepticism. The diagnostic path still runs through clinical evaluation, imaging, and in many cases, surgery.