The blood tests I wish every woman asked for in her 30s

Why 'normal' isn't the same as optimal

Reference ranges are statistical: they describe the middle 95% of the population that walked into a lab. That population is not healthy by design — it includes people with subclinical thyroid disease, low-grade inflammation, insulin resistance and iron deficiency. Sitting inside that range only means you are not a statistical outlier; it does not mean your physiology is working well (Vincent et al., Clin Chem Lab Med 2019).

Functional medicine uses tighter ranges based on outcomes — the levels at which symptoms resolve and disease risk falls — rather than the levels at which a lab flags you. The two often diverge by a wide margin.

Iron, ferritin and the silent tax on energy

Ferritin is the storage form of iron. NHS labs typically flag deficiency below 15 µg/L, but symptoms of low iron — fatigue, hair shedding, restless legs, breathlessness, low mood — appear well before that. A 2022 BMJ review concluded that women of reproductive age frequently develop symptomatic iron deficiency at ferritin levels between 15 and 50 µg/L, especially in the presence of heavy menstrual bleeding (Pasricha et al., BMJ 2021).

I want to see ferritin closer to 50–80 µg/L in menstruating women, alongside a full iron panel (serum iron, transferrin saturation, total iron-binding capacity) and CRP to make sure ferritin isn't falsely elevated by inflammation.

Thyroid: TSH alone tells you almost nothing

A TSH inside the wide NHS range (roughly 0.3–5.5 mIU/L) misses the majority of early thyroid dysfunction. A proper panel includes TSH, free T4, free T3, reverse T3 and both thyroid antibodies (TPO and TG). Hashimoto's antibodies can be raised for years before TSH ever drifts, and around 1 in 10 women carries them (Hollowell et al., J Clin Endocrinol Metab 2002).

Optimal TSH for symptomatic women is generally 1.0–2.0 mIU/L with free T3 in the upper half of range. A woman with a TSH of 4.0, fatigue, hair loss and cold hands is not 'normal' just because the lab didn't flag her.

Sex hormones — timed properly

Oestradiol, progesterone, LH, FSH, SHBG, total and free testosterone, DHEA-S. In a cycling woman, progesterone must be drawn 7 days before the expected next period (mid-luteal); a Day 21 test is only correct if you have a 28-day cycle. Off-cycle, the result is meaningless.

Low progesterone in the luteal phase is one of the most common drivers of PMS, sleep disturbance, anxiety and heavy bleeding, and is almost always missed on standard panels because it isn't tested (Prior, Endocr Rev 2018).

Metabolic health — the under-50 silent epidemic

Fasting glucose is a poor early marker. Fasting insulin, HbA1c and HOMA-IR catch insulin resistance years before glucose ever drifts. Around 1 in 8 lean women in their 30s already has insulin resistance, and it is a major upstream driver of PCOS, acne, miscarriage, fatigue and stubborn weight gain (Reaven, Annu Rev Med 1993; Diamanti-Kandarakis & Dunaif, Endocr Rev 2012).

I want to see fasting insulin under 7 µIU/mL, HbA1c under 5.4%, triglyceride-to-HDL ratio under 1.5 — not just glucose under the diabetic threshold.

Inflammation and nutrient status

hs-CRP picks up low-grade systemic inflammation that ordinary CRP misses. Vitamin D should sit between 75 and 125 nmol/L for immune and bone function, not just above the deficiency cut-off of 50 (Holick, N Engl J Med 2007). B12 should be above 400 pg/mL, with active B12 (holotranscobalamin) and MMA if symptoms suggest functional deficiency despite a 'normal' serum level (Allen, Am J Clin Nutr 2009).

Magnesium RBC is a far better measure than serum magnesium, which is tightly regulated and rarely abnormal even when tissue stores are depleted.

The minimum panel I want every woman in her 30s to run once

• Full iron studies + ferritin + hs-CRP
• Full thyroid panel including free T3, reverse T3, TPO and TG antibodies
• Cycle-timed sex hormones: oestradiol, progesterone, LH, FSH, SHBG, total/free testosterone, DHEA-S
• Fasting insulin, HbA1c, fasting glucose, full lipid panel
• Vitamin D, active B12, folate, magnesium RBC, zinc, selenium
• hs-CRP and homocysteine for inflammation and methylation

If your GP can't or won't run these, private labs in the UK (Medichecks, Thriva, Randox) and South Africa (PathCare, Ampath) will. Bring the results to a clinician who reads them functionally — the numbers without the interpretation rarely change anything.

References

• Vincent MJ et al. Defining reference intervals: harmonisation, individuality and the limits of population-based ranges. Clin Chem Lab Med 2019;57(1):28–35.
• Pasricha SR et al. Iron deficiency. Lancet 2021;397(10270):233–248.
• Hollowell JG et al. Serum TSH, T(4), and thyroid antibodies in the United States population (1988 to 1994): NHANES III. J Clin Endocrinol Metab 2002;87(2):489–499.
• Prior JC. Progesterone within ovulatory menstrual cycles needed for cardiovascular protection: an evidence-based hypothesis. Endocr Rev 2018;15(1):8–22.
• Reaven GM. Role of insulin resistance in human disease (syndrome X). Annu Rev Med 1993;44:121–131.
• Diamanti-Kandarakis E, Dunaif A. Insulin resistance and the polycystic ovary syndrome revisited. Endocr Rev 2012;33(6):981–1030.
• Holick MF. Vitamin D deficiency. N Engl J Med 2007;357(3):266–281.
• Allen LH. How common is vitamin B-12 deficiency? Am J Clin Nutr 2009;89(2):693S–696S.