Advanced Tiredness and Fatigue Blood Test Kit

TSH is produced by your pituitary gland and controls how much thyroid hormone your thyroid makes. It works in a feedback loop—when thyroid hormones are low, TSH rises to stimulate more production; when thyroid hormones are high, TSH drops. This makes TSH the most sensitive single marker for thyroid dysfunction. Hypothyroidism (underactive thyroid) is one of the most common causes of fatigue—it slows your metabolism, leaving you tired, cold, constipated, and mentally foggy. High TSH indicates hypothyroidism; your pituitary is calling for more hormone because levels are low. Low TSH indicates hyperthyroidism, which causes different symptoms including anxiety, tremor, and weight loss, though fatigue can still occur. Thyroid problems are common and treatable, making TSH an essential part of any fatigue investigation. Results outside the normal range may need a follow-up with your GP.

Free T4 is the unbound, active portion of thyroxine—the main hormone your thyroid gland produces. T4 circulates in your blood and gets converted to the more active T3 in your tissues as needed. Measuring Free T4 alongside TSH helps confirm and characterise thyroid dysfunction. High TSH with low Free T4 confirms overt hypothyroidism. High TSH with normal Free T4 is subclinical hypothyroidism—your thyroid is struggling but still managing to produce enough hormone for now; this can still cause fatigue and often progresses over time. Low TSH with high Free T4 confirms hyperthyroidism. The combination of TSH and Free T4 together gives a clearer picture than either alone. Results outside the normal range may need a follow-up with your GP.

Serum iron measures the amount of iron circulating in your blood, bound to the transport protein transferrin. Iron is essential for making haemoglobin (which carries oxygen to your tissues), producing energy in mitochondria, and supporting immune function and brain chemistry. Low iron directly causes fatigue by reducing oxygen delivery and impairing cellular energy production. Serum iron fluctuates throughout the day (highest in the morning) and is affected by recent meals, so it's best interpreted alongside ferritin, TIBC, and transferrin saturation for the complete picture. Low iron with high TIBC and low ferritin confirms iron deficiency. Low iron can occur even when haemoglobin is still normal—you don't have to be anaemic to have symptomatic iron deficiency. Results outside the normal range may need a follow-up with your GP.

TIBC measures how much iron your blood could carry if all the transferrin protein were fully loaded—it indirectly reflects transferrin levels. When your iron stores are low, your body produces more transferrin to maximise iron capture from your diet, so TIBC rises. When iron stores are adequate or high, less transferrin is needed and TIBC is normal or low. High TIBC is a hallmark of iron deficiency—your body is ramping up transport capacity to compensate for low stores. Low TIBC can occur with iron overload, chronic disease, or malnutrition. TIBC helps distinguish between different causes of low serum iron: in iron deficiency, TIBC is high; in anaemia of chronic disease (inflammation), TIBC is low or normal. Results outside the normal range may need a follow-up with your GP.

Transferrin saturation indicates what percentage of your iron-carrying capacity is actually being used—calculated as (serum iron ÷ TIBC) × 100. It tells you how much of your transferrin 'seats' are filled with iron passengers. Normal saturation is typically 20-50%. Low transferrin saturation (below 20%) is a sensitive marker of iron deficiency—there isn't enough iron to fill the available transport. This can cause fatigue even before haemoglobin drops into the anaemic range. Very high saturation (above 45-50%) can indicate iron overload, which may be relevant for hereditary haemochromatosis—a condition where the body absorbs too much iron. Results outside the normal range may need a follow-up with your GP.

Ferritin is the storage form of iron—it reflects how much iron you have in reserve. It's the most useful single marker for iron status and the first to drop when iron stores are depleted. Low ferritin causes fatigue even before anaemia develops. Many people with ferritin in the 'low-normal' range (10-30 µg/L) experience symptoms that improve when iron stores are replenished—optimal ferritin for energy is often considered 50-70 µg/L or higher, particularly for women. However, ferritin is also an acute phase reactant—it rises with inflammation, infection, and liver disease, which can mask underlying iron deficiency. This is why hs-CRP is included in this panel: if CRP is elevated, a 'normal' ferritin might actually be falsely reassuring. Very high ferritin (above 300-500) warrants investigation for iron overload or other causes. Results outside the normal range may need a follow-up with your GP.

HbA1c measures the percentage of haemoglobin with glucose attached, reflecting your average blood sugar control over the past 2-3 months. It's unaffected by recent meals or fasting status. Fatigue is one of the classic symptoms of diabetes—when blood sugar is poorly controlled, cells can't efficiently use glucose for energy, leaving you tired despite eating. HbA1c below 42 mmol/mol is normal; 42-47 indicates prediabetes (increased risk of developing diabetes); 48 or above is diagnostic of diabetes. Even prediabetes can cause fatigue as your body struggles with insulin resistance. Importantly, HbA1c can catch diabetes and prediabetes that might otherwise go unnoticed—many people with type 2 diabetes have symptoms for years before diagnosis. Results outside the normal range may need a follow-up with your GP.

Folate (vitamin B9) is essential for DNA synthesis, red blood cell production, and cell division. It works closely with vitamin B12—deficiency in either causes similar problems. Low folate causes fatigue directly, and can cause macrocytic anaemia (large, immature red blood cells that don't carry oxygen efficiently). Folate deficiency can occur with poor dietary intake (it's found in leafy greens, legumes, and fortified foods), alcohol excess, certain medications (particularly methotrexate and some anti-epileptics), and malabsorption conditions like coeliac disease. Serum folate reflects recent intake over days to weeks. Note that high-dose folic acid supplementation can mask B12 deficiency on blood tests while allowing neurological damage to progress—this is why B12 and folate are tested together. Results outside the normal range may need a follow-up with your GP.

Active B12 (holotranscobalamin) measures the portion of vitamin B12 that's actually available to your cells—a more accurate marker than total B12. B12 is essential for red blood cell production, neurological function, and DNA synthesis. Deficiency causes fatigue, weakness, neurological symptoms (numbness, tingling, balance problems), cognitive impairment, and macrocytic anaemia. B12 deficiency is common—it affects vegetarians and vegans (B12 is only found naturally in animal products), people over 60 (absorption decreases with age), those with pernicious anaemia (autoimmune destruction of cells needed for B12 absorption), and people taking metformin or proton pump inhibitors long-term. B12 deficiency is treatable but can cause permanent neurological damage if left too long, making screening worthwhile even with vague fatigue. Results outside the normal range may need a follow-up with your GP.

Vitamin D is measured as 25-hydroxyvitamin D, which reflects your body's vitamin D status from both sun exposure and dietary/supplement intake. Vitamin D deficiency is extremely common in the UK—limited sun exposure, indoor lifestyles, and darker skin all increase risk. Low vitamin D causes fatigue, muscle weakness and aches, bone pain, low mood, and impaired immune function. The symptoms overlap significantly with other causes of fatigue, which is why it's included in this panel. Vitamin D deficiency is also associated with depression, which can contribute to fatigue. Levels above 50 nmol/L are generally considered adequate; above 75 nmol/L may be optimal. Many people benefit from supplementation, particularly in winter months. Results outside the normal range may need a follow-up with your GP.

Haemoglobin is the iron-containing protein inside red blood cells that carries oxygen from your lungs to every tissue in your body. It's the key marker for anaemia—low haemoglobin means reduced oxygen-carrying capacity, which directly causes fatigue, weakness, shortness of breath on exertion, and pale skin. Anaemia is defined as haemoglobin below approximately 130 g/L in men and 120 g/L in women, though you can feel tired even with levels at the lower end of 'normal'. Anaemia has many causes—iron deficiency (most common), B12 or folate deficiency, chronic disease, blood loss, and bone marrow problems. The other markers in this panel help identify which type of anaemia you have, which determines treatment. Results outside the normal range may need a follow-up with your GP.

Haematocrit measures what percentage of your blood volume is occupied by red blood cells—the rest is plasma (the liquid portion). Normal haematocrit is roughly 40-50% in men and 36-44% in women. Low haematocrit, like low haemoglobin, indicates anaemia—your blood has fewer oxygen-carrying cells relative to its volume. Haematocrit can also be affected by hydration status: dehydration concentrates the blood and raises haematocrit artificially, while overhydration dilutes it. Very high haematocrit increases blood viscosity and cardiovascular risk. Haematocrit and haemoglobin generally move together and tell a similar story about your red cell status. Results outside the normal range may need a follow-up with your GP.

Red blood cell count measures the actual number of red blood cells per litre of blood. Red cells are produced in your bone marrow and live for about 120 days before being recycled. Low red cell count contributes to anaemia—fewer cells mean less oxygen-carrying capacity. The count, combined with haemoglobin and haematocrit, helps characterise your anaemia. Sometimes red cell count is low while haemoglobin per cell is normal (fewer cells, normal cells); sometimes count is normal but each cell has less haemoglobin than it should. The red cell indices (MCV, MCH, MCHC) help distinguish these patterns and point toward the underlying cause. Results outside the normal range may need a follow-up with your GP.

MCV measures the average size of your red blood cells in femtolitres (fL). Normal MCV is approximately 80-100 fL. This is one of the most important markers for classifying anaemia and determining its cause. Low MCV (microcytic, small cells) typically indicates iron deficiency or thalassaemia—the cells are small because there isn't enough haemoglobin to fill them. High MCV (macrocytic, large cells) suggests vitamin B12 or folate deficiency, alcohol excess, liver disease, hypothyroidism, or certain medications—the cells are larger than normal due to impaired DNA synthesis during production. Normal MCV with low haemoglobin (normocytic anaemia) suggests chronic disease, acute blood loss, or bone marrow problems. MCV is key to directing further investigation. Results outside the normal range may need a follow-up with your GP.

MCH measures the average amount of haemoglobin in each red blood cell, expressed in picograms. Normal MCH is approximately 27-32 pg. MCH generally tracks with MCV—small cells (low MCV) have less haemoglobin (low MCH), and large cells (high MCV) have more haemoglobin (high MCH). Low MCH is seen in iron deficiency anaemia and thalassaemia—each cell is carrying less oxygen than it should. High MCH occurs in B12 or folate deficiency where cells are abnormally large. MCH helps confirm the pattern seen with MCV and contributes to the overall classification of any anaemia present. Results outside the normal range may need a follow-up with your GP.

MCHC measures the concentration of haemoglobin within red blood cells—essentially how 'packed' with haemoglobin each cell is. It's calculated by dividing haemoglobin by haematocrit. Normal MCHC is approximately 320-360 g/L. Low MCHC (hypochromic cells) indicates cells that are pale because they don't have enough haemoglobin relative to their volume—classic in iron deficiency. MCHC is rarely high, but can occur in conditions like hereditary spherocytosis where cells are abnormally shaped and concentrated. MCHC adds another dimension to understanding the characteristics of your red cells and the nature of any anaemia. Results outside the normal range may need a follow-up with your GP.

RDW measures the variation in size among your red blood cells—how much they differ from one another. Normal RDW is approximately 11-15%. A high RDW means your cells vary significantly in size (anisocytosis), which typically indicates active production of new cells of different sizes or destruction of cells at different rates. Elevated RDW is common in iron deficiency anaemia (where new cells are smaller than old cells as iron runs out), B12/folate deficiency, and mixed deficiencies. It can help distinguish between conditions: iron deficiency typically has high RDW, while thalassaemia trait often has normal RDW despite small cells. RDW also has value as a general health marker—elevated RDW is associated with increased cardiovascular risk and mortality, possibly reflecting underlying inflammation or nutritional deficiencies. Results outside the normal range may need a follow-up with your GP.

White blood cells (leukocytes) are your immune system's soldiers, fighting infection and responding to inflammation. Total white cell count measures all types combined. Elevated WBC typically indicates infection, inflammation, or stress response—your body is mobilising immune cells. Very high counts can indicate more serious conditions including leukaemia. Low WBC (leucopenia) can increase infection susceptibility and may occur with certain viral infections, autoimmune conditions, bone marrow problems, or medications. While not a primary cause of fatigue itself, white cell abnormalities can indicate underlying conditions that cause fatigue, and complete blood count provides a comprehensive baseline of blood health. Results outside the normal range may need a follow-up with your GP.

Neutrophils are the most abundant white blood cells, typically comprising 50-70% of your total white count. They're your first-line defence against bacterial infections—they rapidly migrate to infection sites and engulf pathogens. Elevated neutrophils (neutrophilia) commonly indicate bacterial infection, inflammation, or stress. Low neutrophils (neutropenia) significantly increase your risk of bacterial infections and can occur with certain viral infections, autoimmune conditions, chemotherapy, or bone marrow disorders. Neutropenia can cause recurrent infections that contribute to fatigue. The differential white cell count helps characterise any abnormality in total WBC. Results outside the normal range may need a follow-up with your GP.

Lymphocytes are white blood cells responsible for adaptive immunity—they include B cells (which make antibodies), T cells (which kill infected cells and coordinate immune responses), and NK cells (which kill abnormal cells). Lymphocytes typically comprise 20-40% of white blood cells. Elevated lymphocytes (lymphocytosis) often indicate viral infections (like glandular fever/EBV, which classically causes prolonged fatigue), and can also occur with certain chronic infections and lymphocytic leukaemias. Low lymphocytes can occur with HIV infection, after certain viral infections, with immunosuppressive medications, or as part of other conditions. The lymphocyte count helps characterise immune status and identify conditions that might explain fatigue. Results outside the normal range may need a follow-up with your GP.

Monocytes are large white blood cells that circulate in blood before migrating into tissues where they become macrophages—cells that engulf and digest pathogens, dead cells, and debris. They typically comprise 2-8% of white blood cells. Elevated monocytes (monocytosis) can occur with chronic infections (including tuberculosis), inflammatory conditions, certain autoimmune diseases, and some blood cancers. Monocyte elevation may indicate a chronic process worth investigating. Low monocytes are less common and less clinically significant. As part of the complete differential count, monocytes help characterise any white cell abnormality and can point toward chronic conditions that cause fatigue. Results outside the normal range may need a follow-up with your GP.

Eosinophils are white blood cells involved in fighting parasitic infections and in allergic/inflammatory responses. They typically comprise 1-4% of white blood cells. Elevated eosinophils (eosinophilia) occur with allergies (hay fever, asthma, eczema), parasitic infections, certain drug reactions, and some autoimmune conditions. Marked eosinophilia can be associated with conditions that cause fatigue, including adrenal insufficiency and certain vasculitides. In someone with unexplained fatigue, elevated eosinophils might prompt investigation for allergic conditions, parasitic infections (relevant for travellers), or rarer causes. Low eosinophils are typically not clinically significant. Results outside the normal range may need a follow-up with your GP.

Basophils are the least common white blood cells, typically comprising less than 1% of the total count. They play a role in allergic reactions and inflammatory responses by releasing histamine and other chemicals. Elevated basophils (basophilia) are uncommon but can occur with certain allergic conditions, chronic inflammatory disorders, hypothyroidism, and some myeloproliferative disorders (blood cancers). Marked basophilia warrants further investigation. Basophils are rarely low enough to be clinically significant. As the final component of the complete white cell differential, basophils help complete the picture of your immune cell populations. Results outside the normal range may need a follow-up with your GP.

High-sensitivity CRP measures low-level inflammation in your body. CRP is produced by your liver in response to inflammatory signals—the 'high-sensitivity' test detects the subtle elevations relevant to chronic low-grade inflammation, not just the dramatic elevations seen with acute infection. Chronic inflammation is a well-recognised cause of fatigue—it affects energy metabolism, disrupts sleep, and can contribute to feelings of malaise and low mood. Elevated hs-CRP warrants investigation into the source of inflammation, which could include autoimmune conditions, chronic infections, obesity, or other underlying health issues. hs-CRP also serves as a cardiovascular risk marker. Additionally, it helps interpret ferritin—since ferritin rises with inflammation, an elevated hs-CRP suggests your ferritin might be artificially raised rather than reflecting true iron stores. Results outside the normal range may need a follow-up with your GP.

Platelets are cell fragments produced by your bone marrow that form clots to stop bleeding when you're injured. The normal range is 150-400 × 10⁹/L. Low platelet counts (thrombocytopenia) can occur with bone marrow problems, autoimmune conditions, certain infections, and some medications—symptoms include easy bruising and prolonged bleeding. High platelet counts (thrombocytosis) can occur with inflammation, infection, iron deficiency, and certain blood disorders. Platelets are included in this fatigue panel because bone marrow problems affecting red cell production often affect platelets too, and because platelet abnormalities can indicate underlying conditions worth investigating. Results outside the normal range may need a follow-up with your GP.

Mean platelet volume measures the average size of your platelets. Larger platelets are typically younger and more recently released from the bone marrow—they're also more reactive and effective at clotting. MPV provides context for interpreting platelet count. A low platelet count with high MPV suggests platelets are being destroyed or used up faster than normal, and the bone marrow is responding by releasing larger, younger platelets. A low platelet count with low MPV suggests the bone marrow isn't producing platelets effectively. MPV can also be elevated in cardiovascular disease and diabetes. While not directly related to fatigue, MPV helps complete the haematological picture. Results outside the normal range may need a follow-up with your GP.