PCOS is a common endocrine disorder affecting women of reproductive age, characterized by hormonal imbalance. This condition is often recognized through symptoms such as irregular menstrual periods, excess hair growth, and acne. Because the clinical presentation of PCOS can overlap with other health issues, blood tests are essential for confirming the diagnosis and ruling out alternative causes. These laboratory assessments help identify the hormonal and metabolic signatures that define PCOS, guiding long-term management and care.
Primary Hormonal Markers
The presence of elevated male hormones, known as hyperandrogenism, is a defining feature of PCOS that is confirmed through blood analysis. The primary androgens tested are Total Testosterone and Free Testosterone, the biologically active portion. Elevated levels of either form strongly suggest that the ovaries or adrenal glands are producing excessive amounts of these hormones, leading to symptoms like hirsutism and acne.
Dehydroepiandrosterone sulfate (DHEA-S) is another androgen often measured, as it is produced primarily by the adrenal glands. An elevated DHEA-S level can help determine if the source of the androgen excess is the adrenal gland rather than solely the ovaries. Testing for these specific androgens provides the biochemical evidence needed to meet one of the major diagnostic criteria for PCOS.
Luteinizing Hormone (LH) and Follicle-Stimulating Hormone (FSH) are pituitary hormones that regulate the menstrual cycle. While historically, an elevated LH to FSH ratio was considered a hallmark of PCOS, current guidelines suggest this ratio is not a reliable diagnostic marker on its own. Although LH levels are often higher than FSH in many women with PCOS, this finding is inconsistent and insufficient to confirm a diagnosis.
Ruling Out Other Conditions
PCOS is a diagnosis of exclusion, meaning other conditions that mimic its symptoms must be eliminated before a definitive diagnosis. Blood tests serve the function of differentiating PCOS from these look-alike disorders. Thyroid-Stimulating Hormone (TSH) is routinely measured to screen for thyroid dysfunction, as both an underactive and overactive thyroid can cause menstrual irregularities and weight changes similar to PCOS.
Prolactin levels are checked, as elevated levels (hyperprolactinemia) can disrupt ovulation and lead to irregular periods. Non-classical congenital adrenal hyperplasia (NCCAH) is a genetic disorder that can cause androgen excess and is screened for by measuring 17-hydroxyprogesterone (17-OHP). This test helps exclude NCCAH, which is an adrenal condition that presents with symptoms nearly identical to PCOS.
Assessing Metabolic Health
Beyond the reproductive hormones, blood tests are essential for assessing the metabolic health risks associated with PCOS, particularly insulin resistance. Fasting glucose and Hemoglobin A1c (HbA1c) are standard tests used to screen for prediabetes and type 2 diabetes. HbA1c provides an average blood sugar level over the preceding two to three months, offering a long-term view of glucose control.
Fasting insulin levels are also checked, and often used in conjunction with fasting glucose to calculate the Homeostatic Model Assessment for Insulin Resistance (HOMA-IR). A high HOMA-IR indicates that the body is struggling to manage blood sugar efficiently, a factor that can drive the hormonal imbalances of PCOS. Because PCOS increases the risk for cardiovascular disease, a comprehensive lipid panel is also conducted.
This lipid panel measures cholesterol components, including high-density lipoprotein (HDL) and low-density lipoprotein (LDL), along with triglycerides. Women with PCOS often show an unhealthy lipid profile, which are markers of increased cardiovascular risk. Assessing these metabolic markers is central to managing PCOS, even if the results do not confirm the initial diagnosis.
Interpreting Blood Test Results for Diagnosis
No single blood test can confirm a diagnosis of PCOS; rather, the process involves combining laboratory findings with clinical symptoms and imaging results. The most widely accepted diagnostic framework, known as the Rotterdam criteria, requires a patient to meet at least two out of three features after other disorders have been ruled out. Blood tests are used to confirm one of these features: biochemical hyperandrogenism.
The interpretation process involves doctors synthesizing the evidence of elevated androgens (Total Testosterone and DHEA-S) with the patient’s clinical presentation, such as irregular or absent menstrual cycles. Metabolic tests confirming insulin resistance or dyslipidemia are not criteria for the diagnosis itself, but they strongly support the clinical picture and determine the appropriate long-term treatment plan. If blood tests show hyperandrogenism, and the patient also reports irregular periods or an ultrasound reveals polycystic ovarian morphology, the diagnosis of PCOS is confirmed.