Blood tests for athletes in the UK

Why standard reference ranges are built to detect disease, not performance

Standard laboratory reference ranges are statistical, not physiological. They are typically built by measuring a reference population and taking the middle 95 per cent of results, which means the boundaries describe where most people sit rather than where any individual functions well. That design is appropriate for its purpose. NHS testing exists to find and rule out disease, and it does that job well. It was never designed to answer whether an endurance athlete has enough iron to build haemoglobin during a heavy block.

The gap between those two questions is measurable. Work by Galetti and colleagues, published in eClinicalMedicine in 2021, pooled stable iron isotope studies in more than a thousand healthy women and identified the ferritin concentration at which the body starts increasing how much iron it absorbs from food. That inflection point sat at 51.1 micrograms per litre. Below it, absorption is progressively upregulated, which is the body signalling that stores are running down. Most UK laboratory reference ranges place their lower limit for ferritin far below that figure.

Illustrative single value read two ways. Interpretation always depends on symptoms, training load, sex, inflammatory markers and trend over time, not one number in isolation.

Which blood markers matter most for athletes

The markers worth testing in athletes are the ones with a documented link to training capacity, recovery or injury risk, and which can be acted on. Below is what each one tells you and where the evidence is strong or mixed.

Why an athlete's blood results can look abnormal when nothing is wrong

Several markers move predictably in response to training, and each one produces a recognisable false alarm. Knowing which is which is most of the skill in reading athlete bloods.

Creatine kinase rises after loading. Eccentric work, contact sport and unaccustomed sessions all raise it. A high reading days after a hard session usually reflects muscle turnover, not pathology, and Mougios showed athlete reference intervals sit far above non-athlete ones.

Haemoglobin can look low in trained endurance athletes. Plasma volume expands faster than red cell volume, so concentration falls while total oxygen carrying capacity is unchanged or better.

Ferritin can look reassuring after hard training. Ferritin behaves as an acute phase protein, so inflammation pushes it up and can mask depleted stores. This is why the World Health Organization guidance is to measure inflammatory markers alongside it.

Kidney markers can shift with muscle mass and hydration. Creatinine reflects muscle mass as well as kidney function, so estimated filtration rates derived from it can read low in heavily muscled athletes without indicating kidney disease.

None of this means an abnormal result should be waved away. It means the result needs context. Anything that could indicate disease is routed back to a GP, always, and IMULAB reports say so explicitly. Blood test results explained for athletes covers this marker by marker.

How to prepare for a blood test as an athlete

Preparation matters more for athletes than for the general population, because training itself moves several of the markers being measured. The aim is a sample that reflects your baseline rather than your last session.

• Leave a gap after hard trainingAllow at least 24 to 48 hours after a heavy or unaccustomed session before testing, particularly if muscle damage, inflammatory or iron markers are on the panel. Light movement in that window is fine.
• Test in the morning where you canSeveral hormones follow a daily rhythm and are conventionally measured in the morning. Keeping the time of day consistent between tests matters as much as the specific hour, because it makes results comparable.
• Be normally hydratedDehydration concentrates the sample and can shift haematocrit and several other markers. Drink as you normally would. Do not load up immediately beforehand either.
• Follow the fasting instruction you are givenWhether fasting is required depends on which markers are included. Where it is needed, water is allowed. Your booking confirmation will state it.
• Hold new supplements brieflyHigh dose supplements can affect certain readings. If you have recently started something new and want a clean baseline, discuss timing before you book rather than after.
• Note where you are in your cycleFor athletes who menstruate, cycle phase affects several markers. Recording the day makes the result interpretable and future comparisons meaningful.
• Repeat under the same conditionsSame time of day, similar training week, similar hydration. Trend is the most useful output of testing, and trend requires consistency.

How often should an athlete test

Most athletes get the useful information from testing two to three times a year, positioned around the training year rather than at random. A common structure is one test in pre-season to establish a baseline, one mid-season to check whether load is being tolerated, and one after the main competitive block or after a period of heavy volume.

Test more often when there is a reason: a deficiency being corrected and needing rechecking, a symptom that has not resolved, an altitude or heat block, a change in training environment, or a persistent drop in performance that has no obvious explanation. Test less often when nothing has changed. Repeat testing without a question to answer produces numbers, not information.

How blood testing works with IMULAB

IMULAB is a UK performance blood testing company for athletes and high performers. Samples are drawn by trained phlebotomists at Superdrug health clinics across the UK, with at home testing kits availble for some tests including finger prick and a nurse network allowing for at home visits UK wide. You book online, attend your chosen clinic or arrange your sample with a nurse at home or finger prick options. Then receive a report that reads each marker through a performance lens with the underlying evidence stated.

The reports say what a result means for training, what to do about it, and where the evidence is uncertain. Anything clinically concerning is flagged for your GP. Find a clinic near you, or read the specifics for cyclists and mountain bikers.

Frequently asked questions

• What blood tests should an athlete get in the UK?

  The highest value markers for most UK athletes are iron status including ferritin with inflammatory markers alongside, vitamin D, a full blood count, thyroid function, and hormonal markers relevant to energy availability. Markers of muscle, liver and kidney load are useful for interpreting training tolerance. Which of these apply depends on the sport, the training phase and the symptoms, so the panel should follow the question you are trying to answer rather than the other way round.

• Can a blood test tell me if I am overtraining?

  No. There is no blood marker or combination of markers that reliably diagnoses overtraining syndrome. The 2023 International Olympic Committee consensus statement on Relative Energy Deficiency in Sport notes the overlap between low energy availability and overtraining, which makes the two difficult to separate on bloods alone. Blood testing can identify contributors such as iron deficiency or suppressed hormonal markers, but the diagnosis needs training load data, performance history and clinical assessment.

• How long after training should I wait before a blood test?

  Allow at least 24 to 48 hours after a hard or unaccustomed session. Exercise transiently raises creatine kinase and inflammatory markers, and inflammation raises ferritin, which can make depleted iron stores look adequate. Testing in a rested state, at a consistent time of day, gives a result that reflects your baseline rather than your last session.

• Do I need to fast before an athlete blood test?

  It depends which markers are included. Some markers require fasting and some do not, so follow the instruction given at booking rather than a general rule. Where fasting is required, water is allowed and encouraged, because dehydration concentrates the sample and shifts several readings.

• Is a blood test for athletes different from an NHS blood test?

  The laboratory analysis is the same. The difference is the question being asked and the thresholds used to answer it. NHS testing is designed to detect and rule out disease, and it does that job well. Performance testing asks whether a marker sits at a level that supports training, recovery and adaptation, which is a different threshold and often a higher one. A result can be reported as normal by disease criteria while still sitting where research shows an effect on training capacity.

• Can I get an athlete blood test through the NHS?

  Your GP will test when there is a clinical reason, such as symptoms suggesting anaemia, thyroid dysfunction or another condition. NHS testing is not set up to provide routine performance monitoring for healthy athletes, because that is not what it exists to do. If your results suggest a clinical problem, that belongs with your GP, and any private test result that raises concern should be taken to them.

• How often should athletes have blood tests?

  Two to three times a year suits most athletes, positioned around the training year rather than at random intervals. A typical structure is a pre-season baseline, a mid-season check and a post-competition test. Test more frequently when there is a specific reason, such as correcting a known deficiency, investigating unresolved symptoms, or preparing for an altitude or heat block.

• What ferritin level should an athlete have?

  There is no single agreed figure, and anyone quoting one with confidence is overstating the evidence. Research in athlete populations commonly uses a ferritin below 35 micrograms per litre to define the first stage of iron depletion, and a 2021 analysis of iron absorption studies found that absorption begins to increase below approximately 50 micrograms per litre in healthy young women, which suggests stores are being drawn down at that point. Ferritin must be interpreted alongside inflammatory markers, because it rises with inflammation and can therefore mask genuine depletion.

Related reading

• Ferritin levels for athletes: what the evidence supports
• Vitamin D and UK athletes: latitude, testing and supplementation
• Blood testing for cyclists and mountain bikers
• Blood test results explained for athletes