Energy Essentials Blood Test Kit

TSH is produced by the pituitary gland in the brain to control the thyroid gland. It works as part of a feedback loop: when thyroid hormone levels are low, the pituitary releases more TSH to stimulate the thyroid to produce more; when thyroid levels are adequate, TSH production decreases. TSH is therefore the most sensitive initial marker of thyroid dysfunction—it often becomes abnormal before the thyroid hormones themselves move out of range, making it an excellent screening test.

High TSH indicates the pituitary is working harder because thyroid hormone levels are low (hypothyroidism, or underactive thyroid). Hypothyroidism is one of the most common causes of persistent fatigue, affecting about 2% of the UK population and being more common in women and with increasing age. Other symptoms include weight gain, feeling cold, constipation, dry skin, hair loss, and mental sluggishness or 'brain fog.' The good news is that hypothyroidism is easily treatable with thyroid hormone replacement (levothyroxine), and most people feel significantly better once their levels are optimised. Low TSH suggests thyroid hormone levels are too high (hyperthyroidism), which causes different symptoms including anxiety, tremor, and weight loss. Results outside the normal range may need a follow-up with your GP.

Active B12 (holotranscobalamin) measures the biologically available form of vitamin B12 that your cells can actually use, making it a more sensitive and earlier marker of B12 deficiency than total B12. Vitamin B12 is essential for energy production at the cellular level, red blood cell formation, DNA synthesis, and proper nerve function. It's one of the most common vitamin deficiencies and is frequently under-diagnosed because symptoms develop gradually.

B12 deficiency causes fatigue that can be profound—along with other symptoms including weakness, breathlessness, pins and needles or numbness in hands and feet, balance problems, cognitive difficulties ('brain fog'), mood changes, and a sore tongue. If left untreated, B12 deficiency can cause permanent nerve damage, so early identification is important. Risk factors include vegetarian/vegan diet (B12 is found almost exclusively in animal products), older age (reduced absorption), pernicious anaemia (an autoimmune condition), metformin use, and certain gastrointestinal conditions. The good news is that B12 deficiency is easily treated with supplements or injections, and most people notice improvement in energy levels within weeks of starting treatment. Results outside the normal range may need a follow-up with your GP.

Vitamin D is essential for calcium absorption, bone health, muscle function, immune system regulation, and increasingly recognised as important for energy and mood. Despite being called a vitamin, it functions as a hormone and the body produces it when skin is exposed to UVB sunlight. However, in the UK, sun exposure is insufficient during autumn and winter months (October to March) to produce adequate vitamin D, making deficiency extremely common—some estimates suggest up to 1 in 5 UK adults are deficient.

Vitamin D deficiency commonly causes fatigue, muscle weakness and aches, bone pain, and low mood—symptoms that are often attributed to 'just being tired' or 'feeling run down' when there's actually a treatable cause. People at higher risk include those with limited sun exposure (office workers, those who cover their skin, housebound individuals), people with darker skin (more melanin reduces vitamin D production), older adults, and those who are overweight. Levels below 25 nmol/L indicate deficiency; 25-50 nmol/L is insufficient; above 50 nmol/L is adequate; and above 75 nmol/L is considered optimal by many experts. Correcting vitamin D deficiency with supplements can significantly improve fatigue and quality of life. Results outside the normal range may need a follow-up with your GP.