SPORTS PERFORMANCE
Athlete Blood Test UK: What to Test, Results Explained & Sports Performance Guide
You can track every training session, optimise your sleep, eat to fuel performance, and still plateau. Often the missing piece is what you cannot feel: ferritin quietly depleting, vitamin D falling below the threshold where muscle function suffers, or cortisol outpacing testosterone in a ratio that signals your body is no longer adapting to training — it is simply surviving it.
The problem is that standard NHS blood tests are designed to rule out disease, not to optimise performance. A ferritin of 18 µg/L is technically “normal” on an NHS report — but every sports medicine physician worth their salt knows that below 50 µg/L, aerobic capacity and fatigue resistance are measurably impaired. The gap between “not ill” and “ performing at your potential” is where athletes live.
This guide explains which biomarkers matter for athletic performance, why the standard NHS reference ranges are often insufficient for athletes, how to identify overtraining syndrome through blood markers, and what to do when your results come back.
1. Why Athletes Need Blood Testing
Training is a controlled stress. You apply load, the body adapts, and performance improves. But that adaptation depends entirely on the raw materials available — the micronutrients, hormones, and metabolic substrates that power recovery. When those materials fall short, adaptation stalls. You train harder, feel worse, and cannot work out why.
The insidious problem is that subclinical deficiencies often produce no obvious symptoms until they are well established. Ferritin can fall to 20 µg/L — deep into performance-impairing territory — before fatigue becomes obvious, because haemoglobin (the number GP blood tests focus on) remains normal for weeks or months after iron stores are depleted. By the time you feel it, you have been training suboptimally for months.
The British Journal of Sports Medicine has documented the prevalence of relative energy deficiency in sport (RED-S) across both male and female athletes — a syndrome driven by insufficient caloric intake relative to training load that cascades into hormonal disruption, bone stress, immune suppression, and impaired adaptation. Many of the markers for RED-S are only detectable through blood testing.
Three specific blind spots blood testing addresses that no wearable can:
The overtraining blind spot
Elevated resting cortisol, suppressed testosterone, and rising inflammatory markers can precede performance decline by 4-6 weeks. Blood testing lets you catch the physiological signal before the performance consequence becomes apparent.
Subclinical nutrient deficiencies
Vitamin D below 50 nmol/L impairs muscle calcium signalling and immune function. Ferritin below 50 µg/L reduces oxygen-carrying capacity. Neither will show up in how you feel day-to-day until the deficit is severe — but both are easily correctable once identified.
Adaptation monitoring
Retesting after a training block tells you whether your interventions — whether that is dietary, supplementation, or training structure — are actually shifting your physiology. It turns subjective perception into objective data.
2. The 12 Key Biomarkers Every Athlete Should Track
Not all biomarkers are equal in their relevance to athletic performance. These twelve represent the core panel most sports medicine physicians and exercise physiologists recommend, based on evidence for impact on training adaptation, recovery, and injury risk.
Ferritin is the storage form of iron — the reserve that haemoglobin draws on to maintain oxygen-carrying capacity. Athletes, particularly endurance athletes, deplete ferritin faster than sedentary individuals through foot-strike haemolysis, sweat losses, and increased red cell turnover. The critical insight is that ferritin falls long before haemoglobin drops — you can have impaired aerobic capacity and tissue oxygenation with a completely normal haemoglobin. Testing ferritin rather than just haemoglobin is the difference between catching iron depletion early and catching anaemia late.
Vitamin D receptors are expressed in muscle tissue, bone, and immune cells — making it directly relevant to athletic function at multiple levels. Low vitamin D is associated with reduced muscle strength and power output, increased bone stress fracture risk, slower recovery from muscle damage, and higher upper respiratory infection incidence. The NHS defines deficiency as below 25 nmol/L, but exercise physiologists and the evidence behind athletic performance suggest the functional optimal is 75–125 nmol/L. UK latitude means deficiency or insufficiency is common in athletes training through autumn and winter.
Testosterone is the primary anabolic hormone driving muscle protein synthesis, red blood cell production, bone density maintenance, and recovery from training stress. In both men and women, chronically low testosterone relative to personal baseline is a significant marker for inadequate recovery. The Endocrine Society notes that testosterone suppression below physiological thresholds impairs lean mass accrual and increases fatigue. In female athletes, low testosterone (even within the broad 'normal' range) can signal RED-S or HPA axis dysregulation.
Total testosterone is bound predominantly to sex hormone-binding globulin (SHBG) and albumin. Only the free fraction — typically 1–3% — is biologically active. High SHBG (common in athletes with high training volumes, low body fat, or thyroid abnormalities) can suppress free testosterone even when total testosterone looks normal. Measuring free testosterone — or calculating it from total testosterone and SHBG — gives a more accurate picture of anabolic hormone availability.
The cortisol:testosterone ratio is one of the most useful composite markers in sports physiology. Cortisol is catabolic — it breaks down muscle tissue for fuel — and its chronic elevation, driven by training load exceeding recovery capacity, directly antagonises the anabolic effects of testosterone. A resting morning cortisol that is disproportionately high relative to testosterone is a hallmark of overreaching. It also reflects the physiological cost of psychological stress, caloric restriction, and sleep disruption — all common in competitive athletes.
CRP / hs-CRP (high-sensitivity C-reactive protein)
CRP is a liver-produced protein that rises in response to inflammation. In athletes, acute post-exercise CRP elevation is normal and expected — it reflects tissue repair in progress. The concern is chronically elevated CRP at rest, which signals a system that is not fully recovering between sessions. A resting hs-CRP above 3 mg/L in an athlete suggests either overreaching, an underlying infection or immune challenge, or dietary patterns driving systemic inflammation.
TSH and Free T4 (thyroid function)
The thyroid is the metabolic engine. TSH (thyroid-stimulating hormone) and Free T4 together assess whether thyroid output is adequate. In athletes, subclinical hypothyroidism — where TSH is elevated but still within the broad NHS reference range — can manifest as fatigue, impaired thermoregulation, weight gain, and slower recovery without any obvious clinical signs. Female athletes are at higher risk of thyroid dysfunction, and RED-S can suppress thyroid hormone conversion from T4 to T3, the more metabolically active form.
HbA1c reflects average blood glucose over the preceding 2–3 months. For athletes, it is a marker of metabolic efficiency and carbohydrate management rather than disease screening. Athletes who have optimised fuelling strategy will typically have HbA1c in the lower-normal range (32–38 mmol/mol), reflecting efficient glucose disposal. Values trending upward despite high training volume can indicate insufficient carbohydrate intake during training (common in athletes trying to stay lean), inadequate recovery, or early metabolic dysfunction.
Alanine aminotransferase (ALT) and aspartate aminotransferase (AST) are markers of liver cell damage in standard clinical practice. In athletes, however, both enzymes are also released from muscle cells following intense exercise — creating a well-documented artifact where athletes show elevated ALT and AST that looks like liver disease but is simply exercise-induced muscle breakdown. Understanding this context is critical: if you test within 48 hours of heavy training, expect elevated values. Testing in a rest week gives a cleaner baseline.
Serum creatinine is filtered by the kidneys and used clinically to estimate glomerular filtration rate (eGFR). In muscular athletes — particularly strength athletes and bodybuilders — creatinine is naturally elevated due to greater muscle mass, meaning eGFR is often falsely low when standard equations are applied. This routinely generates 'borderline' kidney function results in athletes who have completely normal renal function. Knowing your sport and body composition context is essential for interpreting these results correctly.
The full blood count includes haemoglobin, haematocrit, red blood cell count, MCV (mean corpuscular volume), and white cell count. For athletes, the most relevant values are haemoglobin (oxygen-carrying capacity) and MCV (red cell size — low MCV with low ferritin confirms iron-deficiency anaemia; high MCV with low B12 or folate confirms megaloblastic anaemia). White cell count can flag infection or immune suppression from overtraining. The FBC should always be read alongside ferritin and B12 for a complete picture.
B12 and folate are essential for red blood cell production, DNA synthesis, and neurological function. Both support the methylation cycle, which underpins cellular repair and energy metabolism. Athletes following plant-based diets are at particular risk of B12 deficiency, which does not always produce obvious symptoms until the deficiency is advanced. Folate is critical in female athletes of reproductive age, and insufficiency can impair red cell production, contributing to the fatigue and reduced performance that is often attributed to overtraining.
3. NHS Reference Ranges vs Athletic Optimal Ranges
NHS reference ranges are population-derived statistics: they define the range within which 95% of healthy (sedentary) adults fall. That means 5% of healthy people are flagged as abnormal, and a range designed to catch disease will not identify the much narrower window associated with peak athletic function.
The table below compares standard NHS reference ranges with the evidence-informed athletic optimal ranges used by sports medicine practitioners. The differences are significant.
| Biomarker | NHS “Normal” | Athletic Optimal |
|---|---|---|
| Ferritin | 15–300 µg/L (women: 15–200) | 50–150 µg/L |
| Vitamin D (25-OH) | >25 nmol/L (sufficient) | 75–125 nmol/L |
| Testosterone (men) | 8.0–29.0 nmol/L | 15–25 nmol/L |
| Testosterone (women) | 0.3–2.5 nmol/L | 1.0–2.5 nmol/L |
| TSH | 0.4–4.0 mIU/L | 0.5–2.5 mIU/L |
| HbA1c | <42 mmol/mol (non-diabetic) | 28–38 mmol/mol |
| hs-CRP | <10 mg/L (no acute illness) | <1.0 mg/L (resting) |
| Vitamin B12 | 200–900 pg/mL | 400–700 pg/mL |
| Haemoglobin (men) | 130–170 g/L | 145–165 g/L |
| Haemoglobin (women) | 120–160 g/L | 130–155 g/L |
Important caveat: “Athletic optimal” ranges are informed by sports science literature and clinical experience with athletic populations — they are not established diagnostic thresholds. Individual variation is significant, and your personal baseline trend matters more than any single result. The ranges above are starting points for conversation, not absolute targets.
4. The Overtraining Syndrome Connection
Overtraining syndrome (OTS) is the clinical endpoint of accumulated training stress that exceeds the body's capacity to recover. It is distinct from the functional overreaching that is a normal part of progressive training — OTS represents a deeper physiological breakdown that can take weeks to months to resolve and significantly impairs performance.
The challenge is that OTS has no single diagnostic test. A BMJ review of overtraining syndrome notes that diagnosis is largely clinical, based on the exclusion of other causes (illness, iron deficiency, thyroid dysfunction) combined with a history of excessive training load and persistent performance decline. This is precisely why blood testing is valuable — it both rules out other causes and identifies the hormonal and inflammatory signature of overreaching.
The cortisol:testosterone ratio has the strongest evidence as a blood-based overtraining marker. Studies in endurance and strength athletes have found that a sustained decline of 30% or more from personal baseline in the testosterone:cortisol ratio correlates with impaired recovery and overreaching. Note that this is a ratio and a trend — the absolute numbers matter less than the direction of travel from your own established baseline.
Relative Energy Deficiency in Sport (RED-S) is a related but distinct syndrome that occurs when energy availability falls below the threshold needed to support both training and normal physiological function. The British Journal of Sports Medicine IOC consensus on RED-S identifies the following blood test findings as characteristic of the syndrome:
Heart rate variability (HRV) from wearables provides a useful real-time signal of autonomic stress, but blood testing provides the physiological explanation for why HRV is declining — is it iron, hormones, inflammation, or thyroid? Each has a different intervention. Without blood data, you are managing symptoms rather than causes.
5. Sport-Specific Considerations
Not all biomarkers are equally relevant to all sports. The profile of physiological stressors varies significantly between endurance athletes, strength-based athletes, and team sport players — and your testing priorities should reflect that.
Endurance athletes (running, cycling, triathlon, rowing)
Iron status is the highest priority. Ferritin, haemoglobin, and haematocrit collectively tell you whether oxygen delivery is optimised. Foot-strike haemolysis (red blood cell destruction with each running stride) is a real and measurable phenomenon in distance runners, particularly those logging high mileage on hard surfaces. Vitamin D and cortisol (for overtraining screening) are also highly relevant given the high training volumes typical in endurance sport.
Strength athletes (powerlifting, weightlifting, bodybuilding)
Testosterone and free testosterone are the primary markers of anabolic status and recovery capacity. Liver enzymes (ALT/AST) are regularly elevated due to muscle breakdown and should be interpreted with the exercise artifact in mind. Creatinine will be elevated in muscular athletes — this does not indicate kidney disease. Vitamin D matters for bone health and testosterone synthesis.
Team sport athletes (football, rugby, hockey, basketball)
The combination of high-intensity repeated sprint efforts, contact exposure, and congested fixture schedules creates a specific stress profile. CRP and iron are both important given the inflammation from contact and the travel/congested schedule. Testosterone and cortisol are useful for monitoring recovery across competitive seasons. Vitamin D matters for injury prevention and immune resilience during the winter fixture run.
6. Female Athlete-Specific Concerns
Female athletes face a distinct set of physiological challenges that male-focused sports science has historically underserved. Several of these have direct blood test implications.
Iron loss through menstruation
Menstrual blood loss is the most common driver of iron deficiency in premenopausal women. A heavy period can represent losses of 30–80 ml of blood — equivalent to 15–40 mg of iron — which must be replaced through diet. Female athletes who combine high training volumes with heavy menstrual losses are at high risk of progressive ferritin depletion. NICE guidelines on iron deficiency note that menstrual blood loss is the most common cause in women, yet GP testing often only occurs once symptoms of frank anaemia develop.
Low energy availability and RED-S
Low energy availability — where total caloric intake minus exercise energy expenditure falls below approximately 30 kcal/kg lean mass/day — is common in female athletes, particularly in aesthetic sports (gymnastics, dance, figure skating) and endurance sport. The BJSM IOC consensus identifies the female athlete triad as a subset of RED-S: the interplay of low energy availability, menstrual dysfunction (ranging from luteal phase defects to full amenorrhoea), and reduced bone mineral density. Blood testing can quantify the hormonal impact: oestrogen, LH, FSH, and cortisol are the key markers.
Thyroid sensitivity
The thyroid gland appears more sensitive to the effects of energy restriction and training stress in women than in men. Subclinical hypothyroidism — a TSH between 2.5 and 4.0 mIU/L with normal Free T4 — is more prevalent in female athletes and may contribute to fatigue, weight management difficulties, and impaired recovery even when all other markers are normal. The conversion of T4 to the active T3 form can also be impaired by caloric restriction, meaning TSH and Free T4 can look normal while tissue-level thyroid activity is reduced.
Testosterone in female athletes
Testosterone is often framed as exclusively male, but it plays an important role in female athletic function — supporting libido, energy, muscle protein synthesis, and bone maintenance. The lower end of the female testosterone reference range is very broad: values of 0.3 nmol/L are technically 'normal' but associated with fatigue, reduced muscle development, and poor recovery in active women. In female athletes, testosterone in the upper half of the reference range (1.0–2.5 nmol/L) is more consistent with optimal recovery and adaptation.
Female athletes experiencing menstrual irregularity — cycle lengthening, skipped periods, or amenorrhoea — should treat this as a physiological warning signal requiring investigation, not a normal consequence of hard training. The British Journal of Sports Medicine is unambiguous on this point: menstrual dysfunction in athletes signals a level of energy deficit that is harming bone health, hormonal function, and long-term health outcomes.
7. Common Athlete Blood Test Patterns
Blood results rarely tell a story in isolation. Four patterns appear frequently in athlete testing, each with a distinct physiological narrative and response strategy.
Pattern A
High cortisol + low testosterone + elevated CRP → Overreaching
This is the hormonal and inflammatory signature of an athlete whose training load has consistently exceeded recovery capacity. Cortisol is chronically elevated because the HPA axis has been activated repeatedly without full resolution. Testosterone has been suppressed — partly because cortisol and testosterone compete for the same precursor (pregnenolone), and partly because the HPG axis downregulates under systemic stress. CRP elevation confirms that recovery inflammation is not resolving between sessions. The intervention is mandatory: reduce training volume by 40–60% for 2–4 weeks, prioritise sleep, and increase caloric intake. Retesting after a structured deload will usually show measurable improvement within 4–6 weeks.
Pattern B
Low ferritin + normal haemoglobin → Iron depletion without anaemia (the hidden epidemic)
This is perhaps the most common performance-limiting pattern in athletes — and the most commonly missed by standard GP testing, which focuses on haemoglobin. Ferritin below 50 µg/L in athletes is associated with measurably reduced VO2 max, increased perceived exertion at given workloads, and impaired exercise economy. The NICE guidance on iron deficiency anaemia notes that the threshold for treatment in symptomatic individuals is lower than the reference range implies. In practice, many sports medicine physicians treat ferritin below 30–50 µg/L in athletes regardless of haemoglobin status, particularly when symptoms support it.
Pattern C
Low vitamin D + elevated PTH → Bone stress risk
When vitamin D is insufficient, the parathyroid glands compensate by increasing parathyroid hormone (PTH) output to maintain serum calcium — doing so by increasing calcium resorption from bone. This is particularly relevant for athletes logging high impact volumes (running, gymnastics) where cumulative bone stress is already high. The combination of low vitamin D (below 50 nmol/L) with elevated PTH is a meaningful signal for bone stress fracture risk. Addressing it — through vitamin D3 supplementation to bring levels to 75–125 nmol/L — typically normalises PTH within 8–12 weeks.
Pattern D
Elevated ALT/AST + normal CK → Exercise artifact, not liver disease
Both ALT and AST are released from skeletal muscle following intense exercise — a fact that is not always reflected in GP consultation notes, because liver disease is the primary clinical context in which these markers are elevated. Creatine kinase (CK) is a more specific muscle marker, but it is not always included in standard panels. If you test within 24–72 hours of heavy training and see elevated ALT/AST, the correct interpretation in an otherwise healthy athlete is exercise-induced muscle enzyme release, not hepatitis. Retesting in a rest week will confirm this — values should return to normal within 5–7 days of training cessation.
8. GP vs Helvy: Athlete Blood Testing Comparison
NHS GP testing is excellent for disease detection. For performance optimisation in healthy, active individuals, it has structural limitations that are worth understanding before you decide where to test.
| NHS GP | Helvy | |
|---|---|---|
| Markers tested | FBC, ferritin, and TSH if symptoms warrant. Testosterone or cortisol only if pathology suspected. | 16 markers including cortisol, testosterone, free testosterone, TSH, Free T4, ferritin, FBC, HbA1c, liver function, kidney function, lipids, and vitamin D. |
| Reference ranges | Population-normal ranges designed to catch disease, not optimise performance. | Results contextualised against athletic optimal ranges with sport-aware interpretation. |
| Turnaround | Appointment wait of days to weeks. Results may take a further 3–5 working days. | Home finger-prick kit. Results within 5 working days of sample receipt. |
| Sports context | No awareness of exercise-induced artifacts (elevated ALT, elevated creatinine in muscular athletes). | Interpretation notes exercise context, flags when elevated enzymes are likely exercise artifacts. |
| Cost | Free to the patient (funded by NHS) — but requires GP to agree the test is clinically indicated. | £149 for the Performance panel. No GP referral needed. |
| Retest frequency | Retesting for non-pathological findings is generally not supported on the NHS. | Retest at any point — every 3 months recommended for tracking training periodisation. |
| Digital tracking | Results may be accessible via NHS app but not presented as longitudinal trends. | All results stored in your dashboard with trend lines, so you can see direction of travel across multiple tests. |
The two approaches are complementary, not mutually exclusive. If your Helvy results identify a genuine clinical concern — very low testosterone, elevated TSH, markedly low haemoglobin — your GP should be your next call. The two should work together, not as alternatives.
PERFORMANCE PANEL
16 Biomarkers, Sport-Aware Interpretation
The Helvy Performance panel covers every marker in this guide: ferritin, vitamin D, testosterone (total + free), cortisol, hs-CRP, TSH, Free T4, HbA1c, full blood count, liver function, kidney function, and lipids. Home finger-prick kit, results in 5 working days.
See the Performance panel — £1499. When to Test During Your Training Cycle
The timing of your blood test relative to your training cycle materially affects what you can learn from the results. Testing mid-block when training stress is at its peak will produce different results from testing during a deload — both are useful, but for different questions.
Pre-season or pre-block baseline
Test 1–2 weeks before beginning a new training cycle
Establish your personal baseline values across all markers. This is the reference point against which all future results are compared. Pre-season testing also identifies any deficiencies (iron, vitamin D) that would limit your response to training if not addressed before the block begins.
Mid-block monitoring
Test 4–6 weeks into a structured training block
Captures the physiological response to accumulated training load. Elevated cortisol, falling ferritin, and rising CRP at this point are normal responses to training stress — the question is whether they are within acceptable bounds or signalling overreaching. This test asks: is the body adapting or breaking down?
Recovery phase / deload week
Test during or immediately after a planned deload
The cleanest results, closest to your true resting physiology. Exercise artifacts in liver enzymes and creatinine are minimised. This test is most useful for annual health monitoring, catching deficiencies, and assessing whether the previous block was recovered from adequately.
Post-supplementation check
8–12 weeks after starting vitamin D, iron, or other interventions
Confirms that supplementation has achieved the target range. Vitamin D typically takes 8–10 weeks to reach steady state. Iron repletion (with ferrous sulfate under GP guidance) typically takes 8–12 weeks to restore ferritin. Testing confirms efficacy before you reduce or discontinue.
If you train year-round without structured periodisation, a minimum of two tests per year — one in winter (when vitamin D is lowest) and one in summer — captures the seasonal variation in the markers most sensitive to sunlight exposure and immune stress.
10. What to Do With Your Results
Not all out-of-range results require the same response. A rough framework for categorising what action is needed:
Lifestyle and nutrition intervention first
Relevant markers: Vitamin D (mildly low: 30–50 nmol/L), ferritin (borderline: 30–50 µg/L in a well-nourished athlete), elevated cortisol with normal testosterone, mildly elevated hs-CRP
Address through supplementation (vitamin D3 1,000–4,000 IU/day, dietary iron optimisation), training load management, sleep, and stress reduction. Retest in 8–12 weeks to confirm improvement. No medical referral required in the first instance.
Supplement under GP guidance
Relevant markers: Confirmed iron deficiency (ferritin <20 µg/L, or low ferritin with low haemoglobin), severe vitamin D deficiency (<25 nmol/L)
Your GP may recommend prescribed iron supplementation (ferrous sulfate) at doses not appropriate for self-supplementation, or loading doses of vitamin D. A brief GP conversation or private GP appointment is appropriate. Helvy results are accepted as a basis for this conversation.
Medical investigation required
Relevant markers: TSH outside 0.4–4.0 mIU/L, testosterone well below the reference range, haemoglobin below 120 g/L (women) or 130 g/L (men), markedly elevated CRP (>10 mg/L) with no obvious cause
Book a GP appointment and bring your Helvy results. These findings warrant clinical evaluation to rule out thyroid disease, hypogonadism, anaemia, or an unidentified inflammatory source.
11. Supplements That Actually Matter for Athletes
The supplement industry generates billions annually by marketing products with marginal evidence to athletes with genuine performance ambitions. Blood testing cuts through this: if a supplement addresses a deficiency your test has identified, it is worth taking. If it does not, it is background noise. Here is how the evidence stacks up, broadly aligned with the ACSM position stand on nutrition and athletic performance.
STRONG EVIDENCE
Creatine monohydrate
The most robustly evidenced performance supplement in sports science. 3–5g per day increases muscle phosphocreatine stores, supporting high-intensity effort capacity and improving recovery between sets and sprints. Relevant to strength and team sport athletes. Does not require blood testing to validate use — the evidence is strong enough to justify supplementation regardless.
Vitamin D3 (if deficient or insufficient)
Only worth supplementing if your blood test shows levels below 75 nmol/L. Target 75–125 nmol/L. 1,000–4,000 IU/day is the typical effective range for maintenance; higher loading doses may be appropriate under GP guidance if severely deficient. Take with vitamin K2 to support calcium directionality.
Iron (if ferritin is confirmed low)
Iron supplementation is effective and important when ferritin is confirmed below 30–50 µg/L with supporting symptoms. But iron is pro-oxidant at sufficient doses — do not supplement without a blood test confirming the need. Dietary iron from red meat, dark leafy greens, and legumes is preferable to supplementation where intake can be optimised. If supplementation is required, ferrous sulfate or ferrous bisglycinate are the most evidence-based forms.
MODERATE EVIDENCE
Omega-3 fatty acids (EPA + DHA)
2–3g per day of combined EPA+DHA has shown benefit for reducing exercise-induced inflammation, supporting muscle protein synthesis in older athletes, and potentially improving HRV. Most relevant if you eat little oily fish. Not detectable on standard blood panels but a reasonable baseline supplementation choice.
Magnesium glycinate or bisglycinate
Magnesium is involved in over 300 enzymatic processes, including ATP synthesis, muscle contraction, and cortisol regulation. Sweat losses in athletes are significant. Blood magnesium (serum) is a poor indicator of tissue magnesium status — red blood cell magnesium is more informative but not routinely available. 300–400 mg elemental magnesium before bed supports sleep quality and may blunt the cortisol response to training stress.
EMERGING EVIDENCE
Ashwagandha (KSM-66, 600mg/day)
A 2019 randomised controlled trial found KSM-66 ashwagandha significantly reduced serum cortisol vs placebo over 60 days. It also showed modest improvements in testosterone in men with stress-induced dysfunction. Most useful if your blood results show elevated cortisol — may help blunt the cortisol:testosterone ratio in an overreaching state. Takes 8–12 weeks to show meaningful change.
SKIP IF PROTEIN ADEQUATE
BCAAs (branched-chain amino acids)
BCAAs became popular in the 1990s on the basis of mechanistic research suggesting they stimulate muscle protein synthesis. More recent evidence — including the landmark Norton and Layman reviews — shows that BCAAs in isolation stimulate synthesis but cannot complete the process without the other essential amino acids. If you are consuming adequate total protein (1.6–2.2g/kg/day), BCAA supplementation adds nothing. Save the money.
12. When to Retest
The value of blood testing compounds across multiple tests. A single snapshot tells you where you are; a series of tests across time tells you which direction you are heading — and whether your interventions are actually working.
13. Red Flags — When to See Your GP
Most athlete blood test findings fall into the “optimise and monitor” category. But certain results warrant prompt medical review:
Helvy results are clearly formatted and include reference ranges that your GP can interpret. You do not need to have tested via the NHS for your GP to act on a Helvy result — a printed or digital copy of your results is a valid basis for a GP consultation.
14. Frequently Asked Questions
Should I fast before an athlete blood test?
For most markers in the performance panel, fasting is not mandatory — but it improves the quality and comparability of your results. Fasting is important for accurate HbA1c context, cholesterol fractions, and cortisol. A 10–12 hour overnight fast (water and no caffeine permitted) is the standard protocol. Test before 10am to capture the cortisol peak and keep the conditions consistent across all your retests.
Can I test while I am ill?
No — acute illness elevates CRP, suppresses testosterone, and temporarily alters almost every marker in ways that are not informative for performance monitoring. Wait until you have been symptom-free for at least 7 days before testing. If you have been on antibiotics, allow a further 7–10 days.
How soon after a hard training session should I test?
For the cleanest results, avoid intense training for 48–72 hours before testing. ALT, AST, and CRP are all elevated by recent hard exercise and will not reflect your resting physiology. Cortisol is also acutely elevated post-exercise. If testing mid-block for overtraining surveillance, test in the morning on a rest day, not immediately after a session.
My testosterone is 'normal' but I feel terrible — is that possible?
Yes. Two factors can explain this. First, the reference range is very broad — a man at 9 nmol/L and a man at 28 nmol/L are both 'normal', but they may have very different physiological experiences. Second, total testosterone does not tell you how much is biologically available. High SHBG (common in athletes) binds testosterone, reducing the free fraction. Testing free testosterone alongside total testosterone, and tracking your own trend over time, is more informative than a single result judged against the population range.
Is ferritin testing better than standard iron testing?
For athletes, ferritin is the most important iron marker. Serum iron is highly variable day to day and does not reflect stores. Haemoglobin is a lagging indicator — it stays normal until iron stores are substantially depleted. Transferrin saturation is useful when ferritin is ambiguous. Ferritin below 50 µg/L in an athlete with fatigue and declining performance is a clinically meaningful finding, regardless of what haemoglobin shows.
Do female athletes need a different blood test panel?
Female athletes benefit from the same core panel, with particular attention to ferritin (higher depletion risk from menstrual losses), thyroid function (higher baseline risk and RED-S sensitivity), oestradiol and LH/FSH if menstrual irregularity is present, and testosterone in the context of recovery and energy. The Performance panel covers the core markers; if menstrual dysfunction is present, adding oestradiol and LH/FSH via a separate panel is worthwhile.
KNOW YOUR BASELINE
Test Like a Professional Athlete
Helvy's Performance panel covers all 16 markers in this guide — including ferritin, vitamin D, testosterone, cortisol, and full thyroid, metabolic, and liver function. Home finger-prick kit. Results in 5 working days.
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