Add-On Cellular Nutrition Assay

Thiamine pyrophosphate is the active coenzyme for several mitochondrial enzymes in carbohydrate metabolism, including pyruvate dehydrogenase and alpha-ketoglutarate dehydrogenase. Intracellular measurement in lymphocytes is intended to reflect tissue stores more closely than serum thiamine, which responds rapidly to recent intake and may not correlate with functional status.

Chronic thiamine insufficiency impairs oxidative metabolism and can present as fatigue, peripheral neuropathy, or cardiac dysfunction. Intracellular assay is positioned as a functional marker in patients with suspected subclinical deficiency despite normal serum levels, though evidence linking lymphocyte thiamine to clinical outcomes remains limited.

Riboflavin is the precursor of flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN), coenzymes for oxidation-reduction reactions in the mitochondrial respiratory chain, fatty-acid beta-oxidation, and xenobiotic metabolism. Lymphocyte riboflavin is offered as a surrogate for tissue FAD status.

Riboflavin deficiency classically causes angular stomatitis and glossitis but subclinical insufficiency may contribute to fatigue and impaired antioxidant capacity. Intracellular testing is used in functional medicine to identify marginal deficiency in individuals with normal serum riboflavin.

Nicotinamide adenine dinucleotide (NAD) and its phosphorylated form (NADP) are synthesised from niacin and participate in hundreds of redox reactions. Intracellular NAD measurement in lymphocytes is proposed to estimate systemic NAD availability, which declines with age and metabolic stress.

Severe niacin deficiency causes pellagra; subclinical insufficiency is less well characterised. Intracellular NAD is explored in the context of mitochondrial dysfunction, ageing, and chronic fatigue, though the clinical utility of lymphocyte NAD as a predictor of tissue NAD status is not established in consensus guidelines.

Pantothenic acid is the precursor of coenzyme A, essential for fatty-acid synthesis and oxidation, the tricarboxylic acid cycle, and acetylcholine synthesis. Deficiency is rare because the vitamin is widely distributed in foods, but intracellular measurement is marketed to detect marginal insufficiency.

Frank deficiency causes fatigue, paresthesia, and adrenal insufficiency in experimental settings. Subclinical depletion is proposed to impair lipid metabolism and stress response, but evidence linking intracellular pantothenate to clinical outcomes is limited.

Pyridoxal-5'-phosphate (PLP) is the active form of vitamin B6 and serves as a cofactor for more than 100 enzymes, including those in amino-acid metabolism, neurotransmitter synthesis, haemoglobin synthesis, and homocysteine remethylation. Intracellular PLP in lymphocytes is intended to reflect tissue sufficiency.

Vitamin B6 deficiency can cause microcytic anaemia, peripheral neuropathy, and depression. Functional intracellular testing is used to identify marginal deficiency in patients with normal plasma PLP, particularly those with chronic inflammation or alcohol use, which can impair B6 status independently of intake.

Cobalamin is required for methylmalonyl-CoA mutase and methionine synthase, enzymes in fatty-acid oxidation and homocysteine remethylation. Serum B12 may be normal despite tissue deficiency, so intracellular measurement is proposed to better reflect functional status.

Vitamin B12 deficiency causes megaloblastic anaemia and subacute combined degeneration of the spinal cord. Intracellular assay is offered as an adjunct to serum B12 and methylmalonic acid in patients with borderline serum values or unexplained neurological symptoms, though its incremental diagnostic value over serum markers is debated.

Folate, as 5-methyltetrahydrofolate, donates one-carbon units for purine and thymidylate synthesis and homocysteine remethylation. Red-cell folate is the established marker of tissue stores; lymphocyte folate is positioned as an alternative intracellular measure.

Folate deficiency causes megaloblastic anaemia and is associated with neural-tube defects in pregnancy and elevated homocysteine. Intracellular folate is used in functional testing to assess tissue sufficiency independently of recent intake, though red-cell folate remains the consensus standard.

Serum 25-hydroxyvitamin D is the established biomarker of vitamin D status, reflecting hepatic hydroxylation of dietary and cutaneous cholecalciferol. Intracellular 25(OH)D measurement in lymphocytes is proposed to reflect cellular uptake and activation, though its correlation with serum 25(OH)D and clinical outcomes is not well characterised.

Vitamin D is essential for calcium homeostasis and bone health and has immunomodulatory effects. Intracellular assay is marketed to identify cellular insufficiency despite adequate serum levels, a concept that remains exploratory and not endorsed by endocrine or bone-health guidelines.

Magnesium is the second most abundant intracellular cation and a cofactor for more than 300 enzymes, including those in ATP synthesis, nucleic-acid stability, and membrane function. Serum magnesium is tightly regulated and may be normal despite tissue depletion, so intracellular measurement is offered as a functional marker.

Chronic latent magnesium deficiency is proposed to contribute to hypertension, insulin resistance, and arrhythmia. Intracellular magnesium is used in functional medicine to detect subclinical depletion, though evidence that lymphocyte magnesium predicts clinical outcomes or guides replacement therapy is limited.

Selenium is incorporated into selenoproteins, including glutathione peroxidases and thioredoxin reductases, which defend against oxidative stress. Plasma selenium reflects recent intake; intracellular measurement is proposed to estimate tissue selenoprotein activity.

Selenium deficiency can cause cardiomyopathy (Keshan disease) and is associated with immune dysfunction and thyroid disorders. Intracellular selenium is offered as a marker of functional sufficiency in regions with marginal intake or in patients with malabsorption, though its incremental value over plasma selenium is uncertain.

Zinc is a cofactor for more than 300 metalloenzymes and is essential for immune function, wound healing, and DNA synthesis. Serum zinc is influenced by inflammation and albumin, so intracellular measurement is proposed to better reflect tissue stores.

Zinc deficiency impairs cell-mediated immunity, causes dermatitis and diarrhoea, and delays wound healing. Intracellular zinc is used in functional testing to identify marginal deficiency, particularly in patients with chronic infection or malabsorption, though the correlation between lymphocyte zinc and clinical zinc status is not fully validated.

Copper is a component of oxidases and electron-transport proteins, including cytochrome c oxidase and superoxide dismutase. Serum copper and caeruloplasmin are the standard markers; intracellular copper is offered as a measure of cellular availability.

Copper deficiency causes microcytic anaemia and myelopathy; excess (as in Wilson disease) causes hepatic and neurological toxicity. Intracellular copper is used in functional panels to assess balance, though interpretation is complicated by the tight regulation of intracellular copper and lack of validated cutoffs.

Coenzyme Q10 (ubiquinone) is an electron carrier in the mitochondrial respiratory chain and a lipophilic antioxidant. Plasma CoQ10 reflects recent intake and hepatic synthesis; intracellular measurement is proposed to estimate mitochondrial CoQ10 status.

Primary CoQ10 deficiency is a rare mitochondrial disorder; secondary depletion occurs with statin use and ageing. Intracellular CoQ10 is used in functional testing to guide supplementation in patients with fatigue, statin myalgia, or mitochondrial dysfunction, though evidence that lymphocyte CoQ10 predicts clinical benefit is lacking.

Glutathione is the principal intracellular thiol antioxidant, synthesised from glutamate, cysteine, and glycine. It detoxifies reactive oxygen species and xenobiotics and maintains the cellular redox state. Measurement in lymphocytes is offered as a marker of systemic oxidative stress and antioxidant capacity.

Glutathione depletion is proposed to contribute to oxidative injury in chronic illness, toxin exposure, and ageing. Intracellular GSH is used in functional medicine to assess redox status and guide antioxidant or precursor (N-acetylcysteine) therapy, though the clinical utility of lymphocyte GSH as a predictor of outcomes is not established.