18 Signs You Might Need a Blood Test

At Forth, we make it easy to take control of your health with quick, accurate blood tests you can do from home. By measuring key biomarkers, we help you spot early signs of hormone imbalances, nutrient deficiencies, and other hidden issues – before they become bigger problems.

Whether you’re feeling off, chasing a goal, or just want to stay on top of your health, our tests give you clear, personalised insights so you can take action sooner. It’s preventative health, made simple.

Here are 19 signs you could benefit from a blood test.

1. You're constantly ill or unwell

If you’re frequently coming down with colds, feeling run-down, or taking longer than usual to recover from illness, it could be a sign your immune system isn’t functioning at its best. A blood test can help identify underlying issues that may be weakening your immune response. Key markers such as white blood cell count, hs-CRP (C-reactive protein), and vitamin levels (like vitamin D or B12) provide insight into both inflammation and nutritional status – both of which play a crucial role in immunity.

Some deficiencies or imbalances might not be obvious at first. For example, low vitamin D levels can increase susceptibility to infection, while chronic inflammation can leave you feeling constantly fatigued. A blood test helps to take the guesswork out and allows you to take targeted steps to support your immune system through diet, supplementation, or lifestyle changes.

In short, if you’re always the one catching what’s “going around”, it might be time to test what’s going on beneath the surface.

Check Your Immune System

2. You want to check if your diet provides enough nutrients

Whether you’re vegan, vegetarian, gluten-free, or simply trying to eat healthily, it’s not always clear if your diet is covering all your nutritional needs. Blood tests can give you real insight into how well your body is absorbing and using key nutrients.

Markers like vitamin B12, vitamin D, folate, ferritin (iron stores), and magnesium are especially important for people following restricted diets or those who experience symptoms like tiredness, brain fog, hair thinning, or brittle nails. Even small deficiencies can have a big impact on your energy levels, mood, and long-term health.

Testing regularly allows you to spot any gaps and adjust your food choices or take supplements with precision. It also gives peace of mind – rather than relying on guesswork, you can be confident you’re fuelling your body in the best way possible.

If you’re making the effort to eat well, a nutrition blood test can help you understand if it’s actually working for your body.

Check Your Nutrition Health

3. You think you’re going through perimenopause

The lead-up to menopause – known as perimenopause – can bring a rollercoaster of symptoms, from hot flushes and mood swings to poor sleep, brain fog, and irregular periods. But these symptoms are often mistaken for stress or ageing, making it difficult to know if hormones are really the cause.

That’s where Forth’s MyFORM® Perimenopause Test stands out. It’s the only home blood test that uses clinically validated hormone modelling to map how your hormones behave across your menstrual cycle. Instead of relying on a single-day snapshot, MyFORM® uses two blood samples – one taken around day 14 and one around day 21 – to analyse the dynamic changes in your key hormones, including oestradiol, progesterone, FSH, and LH.

This creates a personalised Hormone Health Report showing whether your hormone patterns suggest you’re in perimenopause. It gives you a much clearer, more accurate understanding than traditional one-off tests.

If you’re unsure whether your symptoms are hormonal, MyFORM® offers the certainty and insight you need to take control – whether that’s seeking treatment, adjusting your lifestyle, or simply understanding your body better.

Check Your Hormone Health

4. You're struggling to conceive

Trying for a baby can be an emotional journey, especially when things aren’t happening as quickly as expected. If you’ve been trying to conceive for a while without success, a fertility blood test can provide crucial insights into your reproductive health.

Key markers like FSH, LH, oestradiol, and progesterone help assess whether you’re ovulating regularly and if your cycle is hormonally balanced. In some cases, conditions like polycystic ovary syndrome (PCOS) or thyroid dysfunction can impact ovulation and fertility – both of which can be detected through bloodwork.

Testing at the right point in your cycle is essential for accurate results. Some tests, like progesterone, are most meaningful when measured in the second half of your cycle. Understanding your hormone levels helps guide your next steps – whether that’s making dietary and lifestyle changes, exploring fertility treatments, or simply reducing the anxiety of not knowing what’s going on.

Check Your Hormone Health

5. You're experiencing symptoms of low testosterone

Low testosterone can affect much more than sex drive. If you’re noticing persistent fatigue, reduced muscle mass, low mood, difficulty losing fat, or thinning hair, it might be time to test your testosterone levels.

Testosterone plays a vital role in male health – influencing everything from body composition and energy to mood and motivation. Levels naturally decline with age, but other factors such as stress, poor sleep, and nutritional deficiencies can also contribute to imbalances.

A blood test that includes total testosterone, free testosterone, SHBG (sex hormone-binding globulin), and oestradiol can provide a clearer view of your hormonal health. In many cases, men experiencing symptoms of low testosterone are misdiagnosed or dismissed, especially if they’re still within the ‘normal range’. But a blood test that looks at the full picture can help you advocate for the right treatment or lifestyle changes. Our male hormones test checks the key markers you need to get the complete picture of your hormone balance.

If your energy and vitality aren’t what they used to be, checking your testosterone levels is a good place to start.

Check Male Hormone Health

6. You’re gaining weight easily or feeling fatigued

Weight gain, sluggishness, and brain fog can often be linked to your metabolism – and a blood test can help uncover what’s driving these changes. If you’re gaining weight despite eating well and staying active, or constantly battling fatigue, your blood sugar and insulin regulation may be off.

Markers such as HbA1c (which reflects average blood sugar levels over time) and lipid profile (including triglycerides and cholesterol) offer insight into your metabolic health. Raised levels could indicate insulin resistance – a warning sign that your body is struggling to manage glucose effectively, often preceding type 2 diabetes.

Testing these markers helps detect early changes, even before symptoms become severe. It also highlights whether lifestyle changes are working or need adjusting. Metabolic health is closely linked to long-term outcomes like heart disease, so it’s not just about weight – it’s about preventing future complications and feeling better in your day-to-day life.

Check Metabolic Health

"We’re all guilty of putting up and getting on with it. Work, family life, hobbies; life is busy, but if you’re constantly picking up viruses, feeling under the weather, struggling to perform in the office or at home, maybe taking a second to look at what’s going on the inside maybe a good idea. Getting a better understanding of how your body is coping with life’s stressors is often the first step in making positive changes to improve things. "

Dr Thom Philips

7. You regularly take medications or supplements

Your liver and kidneys work tirelessly to process everything you consume – from medication and alcohol to supplements and environmental toxins. Over time, this can place strain on these vital organs, especially if you’re taking multiple prescriptions, using supplements long-term, or drinking regularly.

A blood test can assess how well your liver and kidneys are functioning, even if you feel fine. Key markers such as ALT and ALP (for liver function), and creatinine and urea (for kidney function) give insight into how efficiently your body is clearing waste and processing compounds.

Sometimes, symptoms like fatigue, nausea, or bloating can be linked to subtle issues in liver or kidney health that go unnoticed without testing. Even if you’re symptom-free, regularly checking these markers is a smart move.

Keeping an eye on these markers ensures your detox systems are working optimally and can flag any issues early before they escalate. It’s about protecting your long-term health, especially when lifestyle or medication load may be placing extra pressure on your body.

Check Liver & Kidney Health

8. You’ve had repeated injuries or aches

If you’re dealing with recurring injuries, unexplained muscle soreness, or slow recovery from training, your blood may hold the answers. Certain markers can reveal whether your body has the right building blocks to support strong muscles and bones – or if something is out of balance.

For example, low vitamin D or calcium can weaken bones, while raised creatine kinase (CK) can indicate muscle stress or breakdown. Athletes are especially prone to overlooking these markers, even though they’re crucial for performance, resilience, and injury prevention.

Other useful indicators include magnesium, which supports muscle contraction and nerve function. Without enough of the right nutrients, your body may struggle to repair and rebuild, leaving you at greater risk of strain, stress fractures, or long-term damage.

A blood test gives you the data you need to take a targeted approach to recovery and training. Because when it comes to performance – prevention is better than treatment.

Check Muscle & Bone Health

9. You have a family history of heart disease

If heart disease runs in your family, it’s worth getting proactive – especially if you’re over 30. A blood test can reveal early signs of cardiovascular risk, long before symptoms appear.

Key markers include total cholesterol, LDL (‘bad’ cholesterol), HDL (‘good’ cholesterol), triglycerides, and hs-CRP (a marker of inflammation). These results can help build a clearer picture of your cardiovascular health and highlight whether changes to your diet, activity levels, or stress management could help protect your heart.

You might feel completely healthy – but inherited risk factors, such as raised cholesterol or lipoprotein(a), aren’t something you can detect without a test. The good news is that with the right insight, many heart disease risk factors can be managed or even reversed.

If heart issues are part of your family history, a simple blood test could give you the insight – and motivation – to make changes that have a long-term impact.

Check Heart Health

"Heart disease is one of the biggest causes of death and disability in the UK today. It’s estimated that 1 in 4 deaths is related to heart disease. The frustrating thing for me as a doctor is that these events are avoidable through early detection and management. Cardiovascular disease doesn’t appear overnight, it takes years for the atherosclerotic plaques to build up to a dangerous level. By testing your lipid markers you are able to assess this long-term risk and make the necessary changes to keep you happy and healthy for longer. "

Dr Thom Philips

10. You’re experiencing weight changes, fatigue, or skin issues

Your thyroid gland plays a key role in regulating your metabolism, energy, and even your skin and hair. If it’s under- or overactive, you might experience a range of vague but frustrating symptoms – like unexplained weight gain or loss, fatigue, thinning hair, dry skin, anxiety, or irregular periods.

A thyroid blood test can bring clarity by measuring levels of TSH (thyroid-stimulating hormone), free T4, and free T3. These markers help determine whether your thyroid is functioning normally, or if it’s contributing to how you feel. In some cases, autoimmune thyroid conditions like Hashimoto’s or Graves’ disease can also be detected by testing thyroid antibodies.

Women are disproportionately affected by thyroid disorders, especially around life stages such as pregnancy or perimenopause, where symptoms often overlap. Without testing, thyroid issues can be missed or misdiagnosed – and left untreated, they can significantly affect quality of life.

If your body feels “off” and you can’t quite put your finger on why, a thyroid test is a smart starting point to rule out a common but often overlooked cause.

Check Thyroid Health

"Thyroid dysfunction (either hyperthyroidism or hypothyroidism) is a surprisingly common problem. The frequency with which this issue occurs rises significantly as people age, and is profoundly impacted by the menopause in women. The symptoms of a misfiring thyroid are often vague and difficult to describe, many people report just feeling slightly more tired, or having disrupted sleep, which once identified and addressed can have massive impacts on people’s wellbeing. "

Dr Thom Philips

11. You’re dealing with anxiety, low mood or brain fog

Not all mental health symptoms originate in the brain – sometimes, they’re driven by what’s happening in the rest of your body. Nutrient deficiencies, hormonal imbalances, and thyroid issues can all contribute to low mood, anxiety, irritability, or poor concentration.

Blood tests can uncover physical factors that might be influencing how you feel mentally. Low levels of vitamin B12, folate, or vitamin D have been linked to symptoms such as fatigue, brain fog, and depression. Similarly, thyroid dysfunction can mimic or worsen mental health symptoms, particularly in women.

It’s not about dismissing the psychological side – but adding a biological lens can offer clarity, direction, and reassurance. For example, if your low energy is actually caused by iron deficiency, addressing that root cause can make a big difference in how you feel emotionally and cognitively.

Mental health is complex, but testing for potential biological contributors helps you take a whole-body approach to wellbeing.

Check Mental Health

12. You’re training hard but not improving

You’re committed to training. You’re eating well, recovering properly, and putting in the work. But the results just aren’t showing. If that sounds familiar, it might be time to take a look at what’s happening internally.

Sports blood tests can reveal whether nutritional deficiencies or hormonal imbalances are holding you back. Key markers like ferritin (iron stores), vitamin D, testosterone, cortisol, and creatine kinase give insight into your recovery, performance capacity, and fatigue levels. Even slightly low iron can impact endurance, while low vitamin D can increase injury risk.

Testing helps personalise your approach. Rather than guessing at supplements or overtraining to see results, you can train smarter – not harder – based on what your body actually needs.

Whether you’re a weekend runner, strength athlete, or training for competition, blood testing provides that extra edge – translating effort into tangible performance gains.

Find Your Edge

"Regular blood testing has been a feature of professional sport for decades. Athletes who are required to perform week in week out at the highest levels want to know exactly how they’re coping with training, and searching for the edge in terms of performance. Our blood testing allows you to access these kinds of insights at home. Understanding how your training is impacting your internal load is a key piece of information in the hunt for more PBs. "

Dr Thom Philips

13. You're constantly tired or burned out

We all feel tired sometimes – but if you’re constantly drained, struggling to get through the day, or waking up exhausted, it’s worth investigating further. Chronic fatigue can stem from a range of biological factors that a blood test can uncover.

Low iron (ferritin), vitamin B12, vitamin D, underactive thyroid function, and even elevated inflammation markers like hs-CRP can all contribute to feeling physically and mentally depleted. Additionally, blood sugar imbalances and cortisol disruption may play a role, especially if you’re under chronic stress or not sleeping well.

Understanding the root cause of fatigue is the first step to resolving it. Rather than guessing whether it’s stress, burnout, or something else, a blood test can show you exactly where your body might need support. The result? A more targeted, effective path back to feeling energised and in control.

Check Energy Levels

14. You're losing hair or noticing skin and nail changes

Sudden hair loss, dry skin, brittle nails or breakouts can be distressing – and while they’re often seen as cosmetic concerns, they’re frequently linked to what’s going on internally.

Blood tests can uncover the real cause. Common culprits include low ferritin (iron stores), low vitamin B12, vitamin D deficiency, or imbalanced thyroid hormones. Hormonal changes (such as high androgens or oestrogen fluctuations) can also contribute to breakouts or scalp changes, particularly in women.

These issues are often dismissed, but they can be early signs of broader nutrient deficiencies or hormonal imbalances. Identifying them through blood testing allows you to address the issue at its root – not just mask the symptoms with topical treatments.

Check Nutrition and Hormones

"These are such simple fixes for quite distressing problems but are often overlooked by NHS GPs. Both the British Association of Dermatologists and the UK Primary Care Dermatology Society acknowledge a clear link between ferritin levels and hair thinning and hair loss. Furthermore there is emerging evidence that people with significant hair thinning and hair loss have much lower levels of vitamin D in their blood. "

Dr Thom Philips

15. You're managing a long-term condition

Living with a condition like PCOS, diabetes, thyroid disease, or high cholesterol means your body needs regular monitoring. Blood testing plays a vital role in managing these conditions and preventing complications.

For example, if you have PCOS, tracking testosterone, SHBG and LH can help manage symptoms. If you’re diabetic, HbA1c and fasting glucose give insight into blood sugar control. And if you have thyroid issues, testing TSH, T4 and T3 ensures your medication is working as intended.

Even if your condition feels stable, regular testing ensures your treatment is still appropriate and catches any early changes before they become issues. It also gives you – not just your doctor – greater insight and autonomy in managing your health.

Monitor a Condition

16. You’ve recently made a lifestyle change

Whether you’ve adopted a new diet, started intermittent fasting, added supplements or ramped up your training, it’s natural to want to know if those changes are making a difference. A blood test offers real, objective feedback.

It can reveal whether your iron stores are improving, if vitamin levels are where they should be, or if your cortisol levels are coping with the new training load. If you’ve gone plant-based, testing B12, iron and vitamin D is especially important.

Rather than guessing or waiting for symptoms to show, testing helps you course-correct early – or reinforces that you’re on the right track.

Keep Track of Changes

17. You're preparing for pregnancy

If you’re planning to get pregnant, checking your blood is one of the most important steps you can take to prepare your body. Nutrient levels and hormone balance play a big role in fertility and healthy conception.

Folate, iron, vitamin D, B12 and thyroid function are essential for both fertility and a healthy pregnancy. For women, testing reproductive hormones like oestradiol, LH, FSH and progesterone can help assess ovulatory function and menstrual health. For men, testing testosterone and sperm-supportive nutrients like vitamin D can offer valuable insight.

Pre-conception blood testing helps you spot – and correct – any imbalances early, giving you a head start on your fertility journey.

Get Ready for Pregnancy

"When you’re thinking about getting pregnant, everyone wants to make sure that their bodies are in the absolute best condition to grow and nurture new life. Getting tested in the lead up can help not only with identifying any issues that may interfere with conception (such as thyroid dysregulation) but also optimise your micronutrient profile ready for growing a whole new person!"

Dr Thom Philips

18. You’re on HRT or TRT

If you’re taking hormone replacement therapy (HRT) or testosterone replacement therapy (TRT), regular blood testing is crucial to ensure your treatment is working effectively and safely.

For those on HRT, monitoring key hormones like oestradiol and progesterone helps confirm that your therapy is achieving the right balance to manage symptoms and protect long-term health, such as bone and heart health. Our female hormone test is perfect for monitoring hormone levels.

For men on TRT, checking testosterone levels, as well as markers like oestradiol and SHBG, ensures you’re within the optimal range without unwanted side effects. Our male hormone test can help effectively track the effectiveness of your TRT.

Everyone’s response to hormone therapy is different. Testing gives you and your healthcare provider clear evidence to fine-tune your treatment, making adjustments where needed to maximise benefits and minimise risks.

"When you’re taking either of these hormonal products regular testing is absolutely key. There are so many factors that can influence the absorption and metabolism of these drugs that, without testing, you really are just stumbling about in the dark. We frequently see customers who have been prescribed hormones with no follow up testing and their levels are wildly outside the recommended ranges. A simple blood test can help guide you and your prescriber to a more effective dosing strategy. "

Dr Thom Philips