Blood values and what they measure
Blood values are measurable substances in your blood. Together they sketch a picture of your energy, recovery and capacity. Look up a value and check its reference range. Each one explains what a high or low result says about your condition.
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Intrinsic Factor Antibodies
Intrinsic Factor Antibodies tests for autoimmune B12 malabsorption. For active individuals with persistently low B12 despite adequate nutrition, this test may help determine if an underlying autoimmune condition is affecting B12 absorption and recovery.
Iodine
Iodine is essential for thyroid function, which regulates metabolic rate and energy availability during exercise. Adequate levels support consistent training performance.
Iron (Serum)
Serum iron indicates current iron availability for oxygen transport during exercise. Low levels can directly impact aerobic performance and recovery time.
Irregular Antibody Screening
An irregular antibody screening test detects unexpected antibodies in your blood that may react against foreign red blood cells. These antibodies can develop after transfusions, pregnancies, or immune stimulation and are important to identify for transfusion and pregnancy safety.
LDH (Lactate Dehydrogenase)
LDH is an enzyme found in nearly every tissue of your body. That includes heart and skeletal muscle. Its full name is lactate dehydrogenase (LDH). This test measures the amount of LDH in the blood. As soon as cells break down, LDH is released into the bloodstream. For anyone training hard, that matters directly. A heavy session damages muscle fibres, so your LDH value rises temporarily. That rise belongs to the recovery process. It says nothing about your liver, even though LDH often sits in a liver panel. So always read the result alongside your CK and AST.
LDL Cholesterol
LDL cholesterol is the blood value that confuses athletes most. You train hard, you eat to plan, and your LDL goes up anyway. That is rarely a measurement error. A high-fat, low-carbohydrate way of eating raises LDL substantially in a proportion of people, and the rise tends to be largest in exactly the lean, well-trained ones. At the same time, your report usually carries no measured LDL at all, but one calculated from your total cholesterol, your HDL and your triglycerides. This page explains when that calculation goes wrong, why the 3.0 mmol/l line is not a goal, and what to track alongside that single number.
LDL/HDL Ratio
The LDL/HDL ratio is your LDL cholesterol divided by your HDL. For anyone who measures their health seriously, this is probably the weakest number on the entire lipid report. No guideline sets a target for it, the number is calculated from an LDL that is itself already calculated, and VLDL and remnant particles do not count towards it. On top of that, endurance training flatters the ratio: HDL rises slightly, the ratio falls, and the amount of harmful cholesterol stays exactly the same. There is one situation in which the number does add something, namely androgen use, because both halves then move the wrong way at once. If you want to steer by something that counts, look at non-HDL cholesterol and ApoB.
LH (Luteinizing Hormone)
LH is a critical pituitary hormone for active individuals, as it regulates sex hormone production that influences recovery, body composition, and training adaptation. Monitoring LH can help detect overtraining-related hormonal disruption.
Lactate
Lactate testing is essential for active individuals to determine training zones, assess aerobic capacity, and monitor the lactate threshold for performance optimisation.
Leptin
Leptin is a hormone produced by adipose tissue that plays a central role in appetite regulation and energy balance. Elevated levels may suggest leptin resistance, where the brain does not respond adequately despite high levels, potentially contributing to weight gain.
Leukocyte Differential
A leukocyte differential test measures the relative proportions of different types of white blood cells in your blood. It provides a detailed breakdown of your immune cell populations, offering valuable insight into your immune system's function.
Leukocytes (WBC)
For an athlete the leukocyte count is above all a trend number. White blood cells respond to exertion within minutes and then fall back. A single isolated measurement therefore says almost nothing about your immune defence. What does say something is the same measurement at comparable moments across a block. At the laboratory that runs the test the usual adult range runs from 4.3 to 10.0 x10^9/L, with the caveat that laboratories differ. Draw rested, not within 24 hours of a hard session, and always read the value alongside the differential.
Lipase
Lipase is essential for fat digestion and energy metabolism, making it relevant for active individuals who rely on efficient nutrient absorption. Monitoring lipase helps ensure the pancreas is functioning optimally to support high-fat recovery meals and performance nutrition.
Lipoprotein(a)
Lp(a) is the one number on your panel that you cannot improve through training. It is an LDL-like particle with an extra protein attached, and its level is more than 90 percent written into your DNA. A training block, a cut or a clean diet will not shift this value to any meaningful degree. That is precisely why you measure Lp(a) once and then know it. A raised value is not a failure and not a project. It is the reason your other targets tighten: your ApoB, your non-HDL, your blood pressure and your insulin sensitivity get less room than they would in someone without this predisposition.
Liver Function Test (LFT)
A liver function test is essential for active individuals who place high demands on their body. Intense training, high-protein diets, and performance supplements are all processed by the liver, making regular comprehensive screening important for sustainable physical performance.
Lymphocytes
Lymphocytes are white blood cells central to your defence against viruses. This is relevant for active people, as intensive training and insufficient recovery can temporarily affect immune defence. A high count often fits a viral infection, while a low count can occur with stress or overload.
MCH (Mean Corpuscular Hemoglobin)
MCH is the average amount of haemoglobin in one red blood cell. Because haemoglobin carries oxygen to working muscle, a low value can show up as fatigue and reduced endurance well before you feel unwell. Learn what your MCH can mean.
MCHC (Mean Corpuscular Hemoglobin Concentration)
MCHC is the average concentration of haemoglobin inside your red blood cells. It is the steadiest of the three red cell indices, so a shift is worth reading carefully alongside your MCV and MCH. Learn what your value can mean.
MCV (Mean Corpuscular Volume)
The MCV blood value is the average volume of a single red blood cell, expressed in femtolitres (fl). The reference range shown on this page is 80 to 100 fl for adults. Below 80 fl the cells are small, above 100 fl they are large, and that direction decides where a low haemoglobin gets investigated. If you train, the movement across seasons is the interesting part: an MCV drifting slowly downwards while still inside the reference range can show something earlier than haemoglobin itself. One isolated result says little about that, two or three side by side say a great deal more.
Magnesium
Magnesium is critical for muscle contraction, energy metabolism, and recovery. Active individuals may have increased needs due to sweat losses and higher metabolic demands.
Magnesium (Intracellular)
Intracellular magnesium provides a true picture of magnesium availability for muscle contraction, energy production, and recovery — essential data for optimising performance.
Melatonin
Melatonin governs your sleep-wake cycle, and sleep is one of the most critical factors in physical recovery and performance. Monitoring melatonin can help identify whether your circadian rhythm supports optimal training adaptation.
Methylmalonic Acid (MMA) (Blood)
MMA Blood measures functional B12 activity at the cellular level. For active individuals, this test may detect subtle B12 insufficiency that could impair red blood cell production, oxygen transport, and muscle recovery before it shows on standard tests.
Methylmalonic Acid (MMA) (Urine)
MMA Urine is a non-invasive functional B12 assessment. For active individuals, this convenient test may help detect cellular B12 insufficiency that could impair oxygen transport, recovery, and endurance without needing a blood draw.