Which Medicare‑eligible blood tests should I order for a reproductive‑age woman with significant pre‑menstrual symptoms and a prior low‑progesterone diagnosis to assess vitamin and hormone status in Australia?

Medicare-Eligible Blood Tests for PMS and Low Progesterone in Australia

For a reproductive-age woman with significant PMS symptoms and prior low progesterone, order the following Medicare-eligible tests: pregnancy test (β-hCG), day 3–6 FSH and LH, day 3–6 estradiol, TSH, prolactin, and mid-luteal progesterone (day 21 or 7 days post-ovulation). 1, 2

Core Hormonal Panel (Early Follicular Phase: Days 3–6)

• FSH and LH should be drawn between cycle days 3–6 to establish baseline pituitary function and assess ovarian reserve, with FSH >10 IU/L indicating diminished ovarian reserve 1, 2
• Estradiol measured on days 3–6 confirms follicular activity and ovarian steroidogenic capacity 1
• LH/FSH ratio >2 strongly suggests polycystic ovary syndrome (PCOS), which can present with PMS-like symptoms and anovulation 1, 2
• TSH is essential because both hypothyroidism and hyperthyroidism disrupt menstrual cycles and can mimic or exacerbate PMS symptoms 2
• Prolactin should be measured as a single morning resting sample, since hyperprolactinemia (>20 µg/L) causes anovulation and menstrual irregularity 2

Mid-Luteal Phase Testing (Day 21 or 7 Days Post-Ovulation)

• Progesterone measurement during mid-luteal phase is the most reliable hormonal indicator of ovulation, with levels <6 nmol/L indicating anovulation 1
• For women with regular 28-day cycles, draw progesterone on day 21; for irregular cycles, draw approximately 7 days after suspected ovulation 1
• Research suggests that days 25–26 may provide optimal diagnostic accuracy for luteal phase deficiency, with a discriminatory threshold of 21 nmol/L (sensitivity 81%, specificity 73%) 3
• Some studies use a threshold of 32 nmol/L to identify subtle ovulation disorders in regularly cycling women 4

Mandatory First Test

• Pregnancy test (β-hCG) must be performed first to exclude pregnancy before interpreting any other hormonal results 2

Additional Testing Based on Clinical Findings

• Total testosterone (drawn days 3–6) if hirsutism, acne, or other hyperandrogenic signs are present, with levels >2.5 nmol/L suggesting PCOS 2
• Androstenedione and DHEA-S if hyperandrogenic manifestations are prominent, to screen for adrenal or ovarian tumors 2
• Fasting glucose and insulin if PCOS is suspected based on clinical features or LH/FSH ratio, with glucose/insulin ratio >4 indicating reduced insulin sensitivity 2

Critical Timing Considerations

• All baseline hormones (FSH, LH, estradiol, testosterone) must be drawn on cycle days 3–6 specifically to ensure accurate interpretation 1, 2
• Progesterone timing is critical: mid-luteal measurement (day 21 for regular cycles, or 7 days post-ovulation) is essential to confirm ovulation 1
• Prolactin must be drawn as a morning resting sample; avoid collection after stress, breast examination, or sexual activity, which cause transient elevations 2

Common Pitfalls to Avoid

• Do not assume normal baseline hormones guarantee ovulation—mid-luteal progesterone is essential to confirm actual ovulation occurred 1
• Women with PCOS may show normal FSH and estradiol but have LH/FSH ratio >2, indicating anovulation despite seemingly normal individual values 1
• Hormonal contraceptives must be discontinued at least 2 months before testing to allow return of normal pituitary-ovarian axis function 1
• Low progesterone alone does not confirm luteal phase deficiency—endometrial biopsy showing >2 days out of phase was historically the gold standard, though serum progesterone is less invasive 5, 3

Evidence Regarding Progesterone and PMS

• Current evidence does not support progesterone supplementation for PMS treatment, as a Cochrane review found insufficient evidence that progesterone helps women with PMS 6
• Research shows progesterone levels were positively correlated with PMS symptoms, preceding symptoms by 5–7 days, suggesting progesterone presence at early luteal levels may be required for symptoms to occur rather than deficiency causing them 7
• Luteal phase deficiency is characterized by decreased integrated luteal phase levels of progesterone, estradiol, and inhibin, along with deficient midcycle LH surge 5

Clinical Context

• Despite the prior diagnosis of "low progesterone," treatment focus should be on confirming ovulatory status and excluding other endocrine causes of her symptoms rather than empiric progesterone supplementation 1, 2
• Vitamin testing (vitamin D, B12, folate, iron studies) can be added based on clinical suspicion but is not part of the standard hormonal workup for PMS 2
• BMI calculation is essential, as obesity is associated with PCOS and menstrual irregularities, while BMI <18.5 kg/m² suggests functional hypothalamic amenorrhea 2