Most people who think about blood tests for nutrients start with vitamin D, iron or B12. Coenzyme Q10 and vitamins A, C, E and K come up less often, usually because someone has a specific reason: a restricted diet, a condition that affects fat absorption, a supplement they want to monitor, or a professional who wants to look at one particular nutrient.
These tests sit in the "with guidance" category. They answer narrow questions well, but they are rarely the first test to reach for. This guide explains what each one measures and what to know before ordering.
Coenzyme Q10
Coenzyme Q10 (CoQ10) is a substance the body makes itself and also gets in small amounts from food. LML describes it as an antioxidant with a central role in energy production inside cells. Reviews explain that it sits in the mitochondria, the parts of the cell that produce energy, and summarise the research on supplements, including the challenges in making supplements that the body absorbs well (Arenas-Jal et al., 2020).
LML lists several uses for the Coenzyme Q10 test, including the assessment of rare mitochondrial and genetic conditions and checking the effect of CoQ10 supplementation. In everyday practice, the second use is the one most people ask about: if you take CoQ10, the test shows the level in your blood.
The fat-soluble vitamins: A, E and K
Vitamins A, E and K dissolve in fat. They are absorbed together with dietary fat, and the body can store them. That means conditions that affect fat absorption can influence their levels, and it also means that very high intakes from supplements can build up over time.
Vitamin A (retinol)
Vitamin A supports vision, the immune system and the health of skin and the linings of the body. It comes in two main forms: preformed vitamin A (retinol), from animal foods, and carotenoids such as beta-carotene, from plants, which the body can convert. A recent review summarises both the effects of too little and the risks of too much, as vitamin A is one of the vitamins where excess can be harmful (Carazo et al., 2021). The VITAMIN A (RETINOL) test measures retinol in the blood. LML asks for the sample to be protected from light.
Vitamin E (alpha-tocopherol)
The NHS explains that vitamin E helps maintain healthy skin and eyes and strengthens the immune system. Good sources include plant oils such as rapeseed, sunflower, soya, corn and olive oil, nuts and seeds, and wheatgerm. The body stores what it does not need straight away. The NHS also notes there is not enough evidence to know the effects of high daily doses from supplements. LML describes the Vitamin E (alpha Tocopherol) test as measuring the main form of vitamin E, an antioxidant that helps protect cells.
Vitamin K
Vitamin K is needed for blood clotting and is also studied for its role in bone. The VITAMIN K (NUTRITIONAL) test reports two forms: vitamin K1 (phylloquinone), found mainly in green leafy vegetables, and vitamin K2 (menaquinone-7). A review of laboratory methods explains that assessing vitamin K status is technically demanding and that different markers answer different questions (Card et al., 2020). LML asks for protection from light and reports results in about 2 weeks.
Vitamin C
Vitamin C is water-soluble and the body cannot make it, so it has to come from food every day. The NHS notes that it helps protect cells, maintain healthy skin, blood vessels, bones and cartilage, and supports wound healing. A severe lack causes scurvy. Citrus fruit, peppers, strawberries, blackcurrants, broccoli, Brussels sprouts and potatoes are good sources.
Blood levels of vitamin C follow intake quite closely, which is one reason a single result is best read alongside diet (Lykkesfeldt and Tveden-Nyborg, 2019). The NHS adds that taking more than 1,000mg a day can cause stomach pain, diarrhoea and flatulence.
The Vitamin C test is the most demanding of this group to collect. LML asks for the sample to be transported to the laboratory without delay, and for the serum to be separated and frozen if transport is delayed.
A combined option
If a professional wants a wider look, Vitamin Profile 1 groups beta-carotene, vitamin A, vitamin E and the B vitamins B1, B2 and B6 in one request.
