Heavy Periods: Labs and Next Steps

What Counts as Heavy Menstrual Bleeding

Clinically, heavy menstrual bleeding (HMB) means losing more than 80 mL of blood per cycle or bleeding for more than seven consecutive days. The American College of Obstetricians and Gynecologists (ACOG) also recognizes any bleeding that interferes with daily physical, social, or emotional quality of life as meeting the threshold for evaluation [1].

Most women do not measure their blood loss in milliliters. That is expected. Practical screening tools like the Pictorial Blood Assessment Chart (PBAC) translate pad and tampon saturation into estimated volumes. A PBAC score above 100 correlates with blood loss exceeding the 80 mL cutoff [2]. Passing clots larger than a quarter, needing to change protection overnight, or doubling up on pads and tampons all suggest volumes in this range.

The old term "menorrhagia" still appears in medical literature, but the FIGO (International Federation of Gynecology and Obstetrics) classification system now categorizes the causes of abnormal uterine bleeding under the PALM-COEIN acronym: Polyp, Adenomyosis, Leiomyoma, Malignancy (structural causes), and Coagulopathy, Ovulatory dysfunction, Endometrial, Iatrogenic, Not yet classified (non-structural causes) [3]. This framework matters because it directly determines which labs and imaging you need.

Why Lab Work Is the First Step

The goal of testing is not simply to confirm that bleeding is heavy. Your clinician already believes you. Lab work answers a different question: what is the bleeding doing to your body, and what is causing it?

A 2019 cross-sectional study of 825 women presenting with HMB at gynecology clinics found that 63% had iron deficiency (ferritin <30 ng/mL) and 33% met criteria for iron-deficiency anemia (hemoglobin <12 g/dL), yet only 36% had been previously tested for either [4]. Dr. Malcolm Munro, Professor of Obstetrics and Gynecology at UCLA and lead author of the FIGO classification system, has stated: "Iron deficiency without anemia is the most common undiagnosed consequence of heavy menstrual bleeding, and it causes fatigue, cognitive changes, and exercise intolerance that women often attribute to other things" [5].

Skipping labs and proceeding directly to treatment means you may miss a coagulation disorder, a thyroid condition, or a ferritin level so low that hormonal management alone will not resolve your symptoms. Testing first also establishes a baseline that makes it possible to measure whether treatment is working at follow-up.

The Core Lab Panel for Heavy Periods

Four categories of blood tests form the standard initial workup recommended by ACOG, the UK's National Institute for Health and Care Excellence (NICE), and the Endocrine Society [1][6][7].

Complete blood count (CBC) with differential. This is the starting point. Hemoglobin below 12 g/dL in a non-pregnant woman indicates anemia. Mean corpuscular volume (MCV) below 80 fL suggests the anemia is microcytic, which points toward iron deficiency as the cause rather than B12 or folate deficiency. Platelet count screens for thrombocytopenia, which can independently cause heavy bleeding.

Iron studies. Serum ferritin is the single most sensitive marker. A ferritin below 30 ng/mL confirms depleted iron stores even when hemoglobin is still normal [8]. Transferrin saturation below 20% adds confirmatory value. The World Health Organization defines iron deficiency as ferritin <15 ng/mL, but many hematologists now treat at the <30 ng/mL threshold because symptoms of depletion begin well before stores are fully exhausted [9].

Thyroid-stimulating hormone (TSH). Both hypothyroidism and hyperthyroidism disrupt the hypothalamic-pituitary-ovarian axis. A TSH outside the 0.4 to 4.0 mIU/L reference range warrants reflex testing of free T4 and, when TSH is suppressed, free T3.

Coagulation screening. ACOG recommends screening for bleeding disorders in any woman with HMB since menarche, HMB unresponsive to standard treatment, or a family history of bleeding disorders [1]. Initial tests include prothrombin time (PT), activated partial thromboplastin time (aPTT), and von Willebrand factor (vWF) antigen and activity (ristocetin cofactor). Von Willebrand disease is the most common inherited bleeding disorder, affecting approximately 1% of the general population, but prevalence among women evaluated for menorrhagia ranges from 5% to 24% across published screening studies [10].

Iron Deficiency: The Problem Behind the Problem

Heavy periods cause iron deficiency. Iron deficiency then causes symptoms that compound the misery of heavy periods. Fatigue, brain fog, restless legs, hair thinning, cold intolerance, and reduced exercise capacity are all documented consequences of low ferritin, even when hemoglobin has not yet dropped below the anemia threshold [8].

A Cochrane review of 10 randomized trials involving 3,273 participants found that intravenous iron replacement produced significantly faster hemoglobin recovery (mean difference 0.9 g/dL at 4 weeks) compared to oral iron in women with HMB-associated anemia [11]. Oral iron remains the first-line option for non-anemic iron deficiency, but absorption is maximized by dosing every other day rather than daily. A landmark crossover study by Stoffel et al. (N=54) published in The Lancet Haematology showed that alternate-day dosing increased fractional iron absorption by 34% compared to consecutive-day dosing due to hepcidin cycling [12].

The practical takeaway: if your ferritin is below 30, you need iron replacement regardless of what other treatments you start for the bleeding itself. If your ferritin is below 15 and your hemoglobin is below 10 g/dL, intravenous iron (ferric carboxymaltose 750 mg x 2 doses or iron sucrose 200 mg x 5 infusions) often becomes the faster, better-tolerated option.

Thyroid Function and Menstrual Flow

Thyroid disorders are present in roughly 10-15% of women with otherwise unexplained heavy menstrual bleeding [7]. Hypothyroidism increases menstrual flow through several mechanisms: reduced hepatic production of sex hormone-binding globulin (SHBG) leads to relatively higher free estrogen levels, which drives endometrial proliferation. Hypothyroidism also impairs platelet function and can reduce levels of clotting factors VII, VIII, IX, and XI [13].

A study published in the Journal of Clinical Endocrinology & Metabolism evaluated 100 women with menorrhagia and found subclinical hypothyroidism (TSH 4.5 to 10 mIU/L with normal free T4) in 22% of participants [14]. After 12 weeks of levothyroxine therapy, menstrual blood loss decreased by a mean of 41% in the treated group.

This is why TSH belongs on the initial panel rather than as a second-tier test. Correcting thyroid function alone resolves heavy bleeding in a meaningful subset of patients, and missing the diagnosis leads to years of unnecessary hormonal or surgical treatment for a problem that required a daily thyroid pill.

Coagulation Disorders: The Diagnosis That Gets Missed

The American Society of Hematology (ASH) 2021 guidelines on von Willebrand disease (vWD) emphasize that heavy menstrual bleeding is the most common symptom leading to diagnosis in women [15]. Yet the average time from symptom onset to vWD diagnosis is 16 years.

Dr. Robert Montgomery, Professor of Pediatrics and Internal Medicine at the Medical College of Wisconsin, has noted: "If a woman has had heavy periods since her very first cycle, screening for von Willebrand disease should be considered standard of care, not a last resort" [15].

Screening involves three tests drawn simultaneously: vWF antigen level, vWF activity (ristocetin cofactor), and factor VIII activity. Results can be falsely normal during acute bleeding, pregnancy, estrogen use, or acute illness because vWF is an acute-phase reactant. Testing during a stable, non-bleeding state on a day when the patient is not taking exogenous estrogen gives the most reliable result.

Type 1 vWD (partial quantitative deficiency) accounts for about 70-80% of cases. Treatment options specific to vWD-related HMB include desmopressin (DDAVP) nasal spray before anticipated heavy flow days, tranexamic acid 1 to 300 mg three times daily during menses, and the levonorgestrel IUD. For women with type 2 or type 3 vWD, vWF-containing factor concentrates may be necessary [15].

Beyond vWD, platelet function disorders, factor XI deficiency, and carrier states for hemophilia A or B can all present as isolated heavy menstrual bleeding. If initial coagulation screening is normal but clinical suspicion remains high (lifelong HMB, easy bruising, prolonged bleeding after dental procedures or surgery), referral to a hematologist for platelet function testing and advanced factor assays is appropriate.

Imaging: When and What to Order

Lab work identifies systemic causes. Imaging identifies structural ones. ACOG and NICE both recommend transvaginal ultrasound (TVUS) as the first-line imaging study for women with HMB who do not respond to initial medical therapy or who have risk factors for structural pathology (age over 45, irregular bleeding pattern, pelvic mass on exam) [1][6].

TVUS detects uterine fibroids with a sensitivity of 95-100% [16]. For intracavitary lesions like polyps and submucosal fibroids, saline infusion sonohysterography (SIS) increases sensitivity from approximately 60% with standard TVUS to over 90% [16].

MRI is not a first-line study. It is reserved for surgical planning when fibroids are large or numerous, when adenomyosis is suspected but TVUS findings are equivocal, or when malignancy cannot be excluded.

Endometrial biopsy is indicated in women over 45, women under 45 with risk factors for endometrial hyperplasia (obesity, chronic anovulation, unopposed estrogen exposure, tamoxifen use), and any woman with HMB that persists despite treatment [1]. The Pipelle biopsy is an office procedure with 99.6% sensitivity for detecting endometrial cancer and 91% sensitivity for hyperplasia in postmenopausal women, though sensitivity in premenopausal women is lower [17].

Treatment Pathways Based on Results

Treatment follows cause. Here is how the most common lab and imaging findings map to first-line interventions.

Normal labs, no structural pathology (ovulatory dysfunction or endometrial cause). The 52-mg levonorgestrel intrauterine system (LNG-IUS, brand name Mirena) reduces menstrual blood loss by 71-95% at 12 months and is recommended as first-line therapy by NICE, ACOG, and the WHO [6][18]. A Cochrane review of 21 trials found the LNG-IUS superior to oral medical therapies (combined oral contraceptives, oral progestins, tranexamic acid, and NSAIDs) for blood loss reduction and patient satisfaction [18].

Alternatives when the LNG-IUS is declined or contraindicated include tranexamic acid 1 to 300 mg three times daily for up to 5 days per cycle (reduces blood loss by 34-54%) [19], combined oral contraceptives (reduce loss by approximately 40-50%), and oral norethindrone acetate 5 mg daily for days 5-26 of the cycle.

Hypothyroidism confirmed. Levothyroxine titrated to normalize TSH, with reassessment of menstrual blood loss at 3 months.

Iron deficiency with or without anemia. Oral ferrous sulfate 325 mg every other day (65 mg elemental iron), or IV iron if ferritin is <15 ng/mL with hemoglobin <10 g/dL. Recheck ferritin at 8-12 weeks. Target ferritin above 50 ng/mL.

Von Willebrand disease or platelet disorder confirmed. Referral to hematology. The LNG-IUS remains effective and is often used in combination with hemostatic agents. Tranexamic acid is the most commonly co-prescribed medication.

Submucosal fibroid or endometrial polyp identified. Hysteroscopic resection is the standard of care for intracavitary lesions causing HMB. For large or numerous fibroids not amenable to hysteroscopy, options include uterine artery embolization, radiofrequency ablation (Acessa), or myomectomy.

Endometrial hyperplasia without atypia. The LNG-IUS achieves regression in 89-96% of cases within 6-24 months [20]. Follow-up endometrial biopsy at 6 months confirms response.

When to Seek Urgent or Same-Day Care

Heavy periods occasionally become dangerous. Go to an emergency department or call your clinician for same-day evaluation if you experience any of the following: soaking through one pad or tampon every hour for two or more consecutive hours, passing clots larger than a golf ball, lightheadedness or dizziness when standing, heart rate above 100 beats per minute at rest, or hemoglobin previously documented below 7 g/dL.

Acute management in the emergency setting typically involves high-dose oral conjugated estrogen (Premarin 2.5 mg every 6 hours) or IV conjugated estrogen (25 mg every 4-6 hours) to stabilize the endometrium, combined with IV iron and sometimes packed red blood cell transfusion if hemoglobin is critically low [1]. Tranexamic acid 1 g IV is an adjunct that reduces bleeding within hours.

Knowing your most recent hemoglobin and ferritin values speeds emergency triage. If you carry a diagnosis of vWD, wearing a medical alert bracelet and keeping a copy of your hematology treatment plan accessible gives the emergency team the information they need to act quickly.

Women who have required emergency intervention for acute HMB should receive definitive management planning (typically LNG-IUS placement or surgical referral) within 2-4 weeks of the acute episode rather than waiting for the next heavy cycle to confirm recurrence [1].