Always tired? These blood tests are worth checking

You sleep seven or eight hours and still wake up exhausted. The afternoon is a black hole, exercise feels like climbing a mountain, and your doctor tells you: “Your blood tests are fine.” Tiredness is one of the most common reasons people see their GP.^[1] Even so, it is often dealt with by checking just five values.

To me, ongoing tiredness isn’t a symptom to be explained away. It’s a signal: somewhere in the system, energy is missing. Where that is can often be narrowed down if the right markers are tested and read properly. That’s what this article is about.

Why so many systems affect your energy

Energy is made in your mitochondria, the power stations of your cells. For them to work, several things have to be right at the same time:

System	Role in your energy	Values that show it
Oxygen transport	Iron and haemoglobin carry oxygen to your cells	Ferritin, transferrin saturation, haemoglobin, MCV
Thyroid	The active hormone T3 sets the pace of your metabolism	TSH, fT4, fT3, TPO and Tg antibodies
Blood formation and nerves	Vitamin B12 and folate are needed for red blood cells and nerve function	Holo-TC, folate, homocysteine, MCV
Fuel	Blood sugar and insulin decide whether energy reaches your cells evenly	Fasting glucose, HbA1c, fasting insulin, HOMA-IR
Inflammation	Inflammatory messengers tell the brain to “rest” and make you tired[2]	hsCRP, ferritin in context
Stress axis	Cortisol follows a daily rhythm and gets you going in the morning[3]	Daily cortisol profile in saliva
Hormones and sleep	Sleep problems become more common in the transition to menopause[4]	Cycle pattern, cycle hormones, symptoms

That’s why a single value rarely explains everything. What matters is the pattern.

Stage 1: The basic blood tests in the guideline

For ongoing tiredness with no obvious cause, the German S3 guideline on fatigue from the German College of General Practitioners and Family Physicians (DEGAM) recommends these tests:^[1]

• Blood glucose: checks for diabetes
• Full blood count: anaemia, signs of inflammation, and clues to vitamin deficiency from the size of the red blood cells (MCV)
• ESR or CRP: inflammation in the body
• Liver function tests (transaminases or γ-GT): strain on the liver
• TSH: a rough screening test for a thyroid disorder

This baseline is sensible for making sure serious illness isn’t missed. But it’s built to find diseases, not deficiencies that make themselves felt long before. One example from the same guideline: ferritin isn’t part of the baseline, even though the guideline itself says iron deficiency can only be largely ruled out from a ferritin of 100 µg/l.^[1]

Stage 2: What I also look at in women

Iron stores: ferritin, transferrin saturation and CRP

Iron deficiency is the most common deficiency I see in women. The blood count only changes late; before that, the stores run empty. In a randomised trial of 198 women who were tired, had normal haemoglobin and a ferritin below 50 µg/l, fatigue fell by 47.7 per cent with iron and by 28.8 per cent with placebo.^[5] And in a meta-analysis of 36 studies, women with hair loss had markedly lower ferritin levels.^[6]

Value	Lab reference (example)	How I read it
Ferritin	approx. 10–150 µg/l	below 30 µg/l, iron deficiency is confirmed;[7] from 100 µg/l, unlikely in otherwise healthy people (DEGAM, IMD Berlin)[1,24]
Transferrin saturation	15–45%	my functional guide value 25–35%
CRP	below 5 mg/l	with inflammation, the WHO already treats a ferritin below 70 µg/l as a sign of iron deficiency[8]

Lab reference values in this article are typical example values; your lab’s range applies.

Thyroid: fT3, fT4 and antibodies

TSH shows the control signal, not the effect. Much of the active T3 is only made in the tissues, through the enzymes DIO1 and DIO2.^[9] In women taking levothyroxine, a normal TSH with a low fT3 isn’t a rare finding: in an analysis of 1,811 treated patients, 15.2 per cent had an fT3 that was too low.^[10] And antibodies can show up long before hormone levels change: in a 20-year study, women with positive antibodies had a roughly eightfold higher risk of later developing an underactive thyroid.^[11] You’ll find everything about these values in “Understanding your thyroid blood tests”.

Value	Lab reference (example)	My functional guide value
TSH	0.22–4.46 mIU/l	below 1.5 mIU/l; over 95% of people with a healthy thyroid are below 2.5[12]
fT4	0.9–1.7 ng/dl (approx. 12–22 pmol/l)	1.1–1.4 ng/dl (approx. 14–18 pmol/l)
fT3	2.3–4.2 pg/ml (approx. 3.5–6.5 pmol/l)	above 3.0 pg/ml (approx. 4.6 pmol/l)
TPO antibodies	below 35 IU/ml	below 9 IU/ml

Vitamin B12 and folate

Vitamin B12 is needed for making blood and for your nerves. A deficiency can leave you tired and forgetful and cause pins and needles long before your blood count looks unusual. The standard serum B12 test isn’t very sensitive to this: only 10 to 20 per cent of the B12 in your blood is in the active form your cells can use, holotranscobalamin (holo-TC). The rest is bound in an inactive form, so total B12 can look normal even though your cells are already getting too little. Holo-TC shows a deficiency earlier.^[22] Women most at risk are those eating a mostly plant-based diet, those with digestive problems and those taking acid-suppressing medication: in a large study, people who had taken them for two years or longer had a 65 per cent higher risk of B12 deficiency.^[13] A clue in the blood count: large red blood cells (MCV above 100 fl).

Value	Lab reference (example)	My functional guide value
Holo-TC (active B12)	below 35 pmol/l deficiency; 35–50 pmol/l grey zone, then test methylmalonic acid; above 50 pmol/l unlikely[22]	above 70 pmol/l
Red cell folate	depends on the lab	more meaningful than serum folate
Homocysteine	below 12 µmol/l	below 7 µmol/l; rises with B12 and folate deficiency

Vitamin D

Vitamin D acts like a hormone in the body and is involved in your muscles and immune system. In Germany, according to the Robert Koch Institute, only 38.4 per cent of adults have adequate levels; 30.2 per cent are deficient.^[23] And a deficiency makes you tired: in a double-blind, placebo-controlled trial of 120 people with fatigue with vitamin D below 20 ng/ml (50 nmol/l), fatigue improved considerably more after a single dose of vitamin D than with placebo; 72 per cent versus 50 per cent reported an improvement.^[21] In people with chronic inflammatory conditions, correcting a deficiency also eased fatigue.^[14] In Hashimoto’s, vitamin D lowered TPO antibodies in a meta-analysis of randomised trials.^[15] That’s why, for me, I always include it in women with fatigue.

Value	Lab reference	My functional guide value
Vitamin D (25-OH-D)	deficiency below 12 ng/ml (30 nmol/l); adequate from 20 ng/ml (50 nmol/l)[23]	50–70 ng/ml (125–175 nmol/l)

Blood sugar and insulin

An energy slump after eating, cravings in the afternoon, tiredness despite enough sleep: in my coaching I often see this in women whose insulin is already raised while their blood sugar still looks normal. Fasting glucose alone doesn’t show it. Fasting insulin is more telling, especially when combined with fasting glucose to calculate HOMA-IR. In a Spanish population study, the cut-off above which HOMA-IR was linked to a higher metabolic risk was about 2.^[16]

Value	Lab reference (example)	My functional guide value
HbA1c	below 5.7% (39 mmol/mol)	below 5.3% (34 mmol/mol)
Fasting insulin	approx. 3–25 mU/l (about 21–174 pmol/l)	below 6 mU/l (about 42 pmol/l)
HOMA-IR	often below 2.5	below 1.5; formula: fasting insulin (mU/l) × fasting glucose (mg/dl) ÷ 405, or with glucose in mmol/l ÷ 22.5

Silent inflammation: hsCRP

When your immune system is switched on all the time, inflammatory messengers send signals to the brain that make you tired, listless and low. Specialists call this sickness behaviour.^[2] Standard CRP mainly picks up acute inflammation. For silent inflammation, high-sensitivity CRP is more precise. My functional guide value is below 0.5 mg/l. A raised hsCRP is also a reason to read a seemingly normal ferritin with caution.^[8]

Stage 3: When there are specific signs

Daily cortisol profile

Cortisol rises sharply in the first 30 to 45 minutes after waking and then falls over the day.^[3] A daily saliva profile shows how well your stress axis keeps to this rhythm. In my work it serves as a guide, not a diagnosis. The term “adrenal fatigue” is not a recognised medical diagnosis in its own right; if genuine adrenal insufficiency is suspected, a doctor always rules it out first. You can read more on my page about exhaustion and the stress axis.

Cycle and hormones from 40

In a large US study of more than 3,000 women, problems falling asleep and staying asleep increased over the transition to menopause.^[4] Poor sleep is then often the direct route to exhaustion. Over 45, according to the UK NICE guideline, perimenopause is recognised from symptoms, not from a blood test.^[17] A cycle diary helps you and your doctor more than a single hormone value.

Minerals in whole blood

Magnesium, zinc and potassium are mostly stored inside the cells. Serum shows only a small part of them. In functional medicine I therefore measure them in whole blood. My functional guide value for magnesium is 34 to 40 mg/l (approx. 1.40 to 1.65 mmol/l).

Sleep apnoea

Pauses in breathing during sleep are often overlooked in women. Menopause is a risk factor in its own right: in a population study, postmenopausal women not taking hormone therapy had sleep apnoea considerably more often than premenopausal women (2.7 per cent versus 0.6 per cent).^[18] Signs are loud snoring, pauses in breathing that someone else notices, a dry mouth and headaches in the morning. If you notice these, see your doctor; assessment often involves a sleep study.

Patterns I often see in my coaching

Pattern	Typical values	What may be behind it
Exhaustion, thinning hair	Ferritin 15–50 µg/l, haemoglobin normal	Iron deficiency without anaemia[5,6]
Tired, always cold, “results normal”	TSH 2.5 up to the lab limit, fT3 in the lower third, TPO antibodies raised	Early Hashimoto’s thyroiditis[11,12]
Still tired on levothyroxine	TSH normal, fT4 on the high side, fT3 on the low side	Reduced conversion of T4 to T3[10]
Tired, forgetful, tingling	Holo-TC below 50 pmol/l, MCV high-normal, acid-suppressing medication	Early B12 deficiency[13]
Slump after eating, cravings	Fasting insulin above 10 mU/l (about 69 pmol/l), HOMA-IR above 2	Early insulin resistance[16]
Exhausted, ferritin “good”	hsCRP raised, ferritin high-normal	Inflammation masking iron deficiency[8]

Patterns are pointers from my coaching experience, not diagnoses. Interpreting your results belongs in a conversation with your doctor.

What blood tests don’t show

According to the German guideline on fatigue, in about 18 per cent of people who see their doctor because of tiredness, depression or an anxiety disorder is behind it.^[1] That isn’t dismissive. It’s a reason to take your mental health seriously too. Medication can also make you tired; ask your pharmacist if you’re unsure. And if your symptoms get markedly worse for days after physical or mental effort, tell your doctor about this specifically.

How to prepare for your appointment

1. For two to four weeks, write down when the tiredness comes, how you sleep, how your cycle goes and what makes the tiredness better or worse.
2. Bring old results with you. Trends say more than a single value.
3. Book your blood test for the morning, because TSH varies considerably over the day.^[19]
4. Tell your doctor’s surgery if you take biotin. It can distort thyroid tests.^[20]
5. Check beforehand which tests your health insurance or health service covers and which you pay for yourself.
6. Don’t change any medication without talking to your doctor first.

Where to start

• My free self-check shows you whether your signs point more towards your thyroid, perimenopause or the stress axis. You’ll then receive the starter guide that matches your result.
• Your free clarity call: 20 to 30 minutes on Zoom. Together we look at where you stand and which next step suits you.

Frequently asked questions

Read on

• Ferritin in women
• Understanding your thyroid blood tests
• Perimenopause, thyroid or iron deficiency?

This article does not replace medical advice. Diagnoses are made by your doctor; changes to medication belong in medical hands.

Sources

1. DEGAM: S3-Leitlinie Müdigkeit [S3 guideline: Fatigue]. AWMF reg. no. 053-002, version 2023-01, long version (recommendation 5.3.1; sections 4.2.1, 4.2.5, 4.2.6). register.awmf.org · Guideline (Germany)
2. Dantzer R et al. From inflammation to sickness and depression: when the immune system subjugates the brain. Nat Rev Neurosci 2008;9:46–56. doi.org/10.1038/nrn2297 · Review
3. Stalder T et al. Assessment of the cortisol awakening response: expert consensus guidelines. Psychoneuroendocrinology 2016;63:414–432. doi.org/10.1016/j.psyneuen.2015.10.010 · Expert consensus
4. Kravitz HM et al. Sleep disturbance during the menopausal transition in a multi-ethnic community sample of women (SWAN). Sleep 2008;31:979–990. · Longitudinal study (n = 3,045)
5. Vaucher P et al. Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial. CMAJ 2012;184:1247–1254. doi.org/10.1503/cmaj.110950 · RCT (n = 198)
6. Treister-Goltzman Y, Yarza S, Peleg R. Iron deficiency and nonscarring alopecia in women: systematic review and meta-analysis. Skin Appendage Disord 2022;8:83–92. doi.org/10.1159/000519952 · Meta-analysis (36 studies, n = 10,029)
7. Naveed K et al. Defining ferritin clinical decision limits to improve diagnosis and treatment of iron deficiency: a modified Delphi study. Int J Lab Hematol 2023;45:377–386. doi.org/10.1111/ijlh.14016 · Delphi expert consensus
8. World Health Organization. WHO guideline on use of ferritin concentrations to assess iron status in individuals and populations. Geneva 2020 (recommendation 1.2). ncbi.nlm.nih.gov/books/NBK569877 · Guideline (WHO)
9. Sabatino L et al. Deiodinases and the three types of thyroid hormone deiodination reactions. Endocrinol Metab (Seoul) 2021;36:952–964. doi.org/10.3803/EnM.2021.1198 · Review
10. Gullo D et al. Levothyroxine monotherapy cannot guarantee euthyroidism in all athyreotic patients. PLoS One 2011;6:e22552. doi.org/10.1371/journal.pone.0022552 · Retrospective study (n = 1,811 vs. 3,875 controls)
11. Vanderpump MP et al. The incidence of thyroid disorders in the community: a twenty-year follow-up of the Whickham Survey. Clin Endocrinol 1995;43:55–68. doi.org/10.1111/j.1365-2265.1995.tb01894.x · Cohort study
12. Wartofsky L, Dickey RA. The evidence for a narrower thyrotropin reference range is compelling. J Clin Endocrinol Metab 2005;90:5483–5488. doi.org/10.1210/jc.2005-0455 · Review
13. Lam JR et al. Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency. JAMA 2013;310:2435–2442. doi.org/10.1001/jama.2013.280490 · Case-control study (25,956 cases)
14. Messina OD et al. Vitamin D in inflammatory rheumatic diseases: still a challenge. Osteoporos Int 2026;37:1221–1231. doi.org/10.1007/s00198-026-08066-7 · Narrative review
15. Jiang H et al. Effects of vitamin D treatment on thyroid function and autoimmunity markers in patients with Hashimoto’s thyroiditis: a meta-analysis of randomized controlled trials. J Clin Pharm Ther 2022;47:767–775. doi.org/10.1111/jcpt.13605 · Meta-analysis of RCTs (n = 258)
16. Gayoso-Diz P et al. Insulin resistance (HOMA-IR) cut-off values and the metabolic syndrome in a general adult population: EPIRCE cross-sectional study. BMC Endocr Disord 2013;13:47. doi.org/10.1186/1472-6823-13-47 · Cross-sectional study (n = 2,459)
17. National Institute for Health and Care Excellence (NICE). Menopause: identification and management. NICE Guideline NG23, sections 1.1 and 1.3. nice.org.uk/guidance/ng23 · Guideline (UK)
18. Bixler EO et al. Prevalence of sleep-disordered breathing in women: effects of gender. Am J Respir Crit Care Med 2001;163:608–613. doi.org/10.1164/ajrccm.163.3.9911064 · Population study
19. Delanghe JR et al. Interpretation of TSH results can be improved by reference values fluctuating in time. Horm Mol Biol Clin Investig 2024;46:21–26. doi.org/10.1515/hmbci-2024-0043 · Laboratory study
20. Bhimireddy N, Na S, Cho E. The implications of biotin supplementation on multiple sclerosis, hair loss conditions, and thyroid disorders. Mult Scler Relat Disord 2026;116:107974. doi.org/10.1016/j.msard.2026.107974 · Review
21. Nowak A et al. Effect of vitamin D3 on self-perceived fatigue: a double-blind randomized placebo-controlled trial. Medicine (Baltimore) 2016;95:e5353. doi.org/10.1097/MD.0000000000005353 · Double-blind RCT (n = 120)
22. LADR Laborverbund. Diagnostik des Vitamin-B12-Mangels: Bedeutung des Holo-Transcobalamins [Diagnosing vitamin B12 deficiency: the role of holotranscobalamin]. LADR informiert Nr. 232. ladr.de · Laboratory information
23. Rabenberg M, Mensink GBM. Vitamin-D-Status in Deutschland [Vitamin D status in Germany]. Journal of Health Monitoring 2016;1(2) (DEGS1). doi.org/10.17886/RKI-GBE-2016-036 · Population data (RKI)
24. IMD Institut für Medizinische Diagnostik Berlin-Potsdam. Ferritin bei Eisenmangel und Eisenmangelanämie: Neue Entscheidungsgrenzen ermöglichen eine differenziertere Beurteilung [Ferritin in iron deficiency and iron deficiency anaemia: new decision limits allow a more differentiated assessment]. Diagnostik-Information Nr. 400, Version 1. imd-berlin.de · Laboratory information