Flavin Mononucleotide Test: FMN Vitamin B2 Active Form

The flavin mononucleotide test measures the active form of vitamin B2 (FMN) in blood. Normal FMN range is typically 10–50 nmol/L. Low FMN levels indicate impaired vitamin B2 activation and possible deficiency, while high levels often reflect supplementation or metabolic imbalance. This test helps assess cellular energy metabolism and vitamin B2 status.

Contents

→ Result interpretation
→ Check your value Flavin Mononucleotide
→ What is Flavin Mononucleotide
→ Reference ranges
→ Causes of abnormal values
→ Flavin Mononucleotide in combination with other markers
→ Possible symptoms
→ When to see a doctor
→ What to do if abnormal
→ Frequently asked questions
→ Related markers

Result interpretation Flavin Mononucleotide

What your result means based on common reference ranges

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Normal

Normal FMN levels indicate adequate vitamin B2 activation supporting energy metabolism and proper mitochondrial function.

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Mildly elevated

Mildly elevated FMN levels usually reflect recent vitamin B2 supplement intake without significant metabolic disruption.

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Significantly elevated

Significantly high FMN levels may suggest metabolic block in FAD conversion or kidney dysfunction affecting vitamin clearance.

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Below normal

Low FMN levels indicate vitamin B2 deficiency, impairing energy production and contributing to anemia or oxidative stress.

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Flavin Mononucleotide, nmol/L

Sex

Age

What is Flavin Mononucleotide?

Flavin mononucleotide is the active coenzyme form of riboflavin (vitamin B2) and plays a central role in mitochondrial energy production and oxidative metabolism. In a blood test, FMN levels reflect how effectively the body converts dietary riboflavin into usable forms like FMN and FAD. This process is essential for ATP generation, antioxidant defense, and cellular repair. Abnormal FMN levels may be linked to conditions such as anemia, chronic fatigue, and metabolic dysfunction. Unlike standard riboflavin testing, FMN provides insight into functional vitamin B2 status and enzymatic activity.

Reference ranges

Group	Normal range	Unit
Men	10 – 50	nmol/L
Women	10 – 50	nmol/L
Children	10 – 50	nmol/L

Causes of abnormal values

Causes of low Flavin Mononucleotide

• Poor dietary intake → insufficient riboflavin reduces FMN synthesis
• Chronic alcoholism → impairs intestinal absorption and activation of vitamin B2
• Malabsorption syndromes → conditions like celiac disease reduce nutrient uptake
• Medication interference → certain antidepressants and diuretics accelerate vitamin depletion
• Phototherapy exposure → light-induced degradation of riboflavin lowers FMN levels

Causes of high Flavin Mononucleotide

• High-dose vitamin B2 supplementation → increases circulating FMN faster than cellular utilization
• Fortified food overconsumption → excess synthetic riboflavin elevates FMN levels
• Genetic enzyme defects → impaired conversion of FMN to FAD leads to accumulation
• Kidney dysfunction → reduced excretion of water-soluble vitamins increases blood levels
• Liver dysfunction → disrupted storage and metabolism of active vitamin forms
• Multivitamin overuse → chronic intake leads to sustained elevated FMN

Flavin Mononucleotide in combination with other markers

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Low FMN + High Homocysteine Indicates impaired folate cycle and increased cardiovascular risk due to B-vitamin deficiency.

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Low FMN + Low Hemoglobin Suggests anemia related to disrupted iron metabolism and reduced erythropoiesis.

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High FMN + High FAD Reflects recent high-dose vitamin B2 supplementation affecting coenzyme balance.

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Low FMN + Low RBC Folate Indicates combined B-vitamin deficiency affecting DNA synthesis and cellular turnover.

Possible symptoms

•Cracks at corners of the mouth (cheilosis)
•Swollen or smooth tongue (glossitis)
•Sensitivity to light (photophobia)
•Red, scaly skin rash (seborrheic dermatitis)
•Fatigue and low energy levels

When to see a doctor

Consult a healthcare professional if FMN levels fall below 10 nmol/L or remain consistently abnormal. Seek medical advice if symptoms like mouth sores, fatigue, or vision sensitivity appear. Persistent high levels without supplementation may require metabolic or kidney evaluation.

What to do if abnormal

🥩 Improve diet: include liver, eggs, dairy, and leafy greens rich in riboflavin
💊 Review supplements: adjust vitamin B2 supplement dosage with a professional
🍽️ Support digestion: treat gut conditions to improve nutrient absorption
🚫 Reduce alcohol: limit intake to restore proper vitamin metabolism
🧪 Monitor levels: repeat blood test to track FMN normalization

The information on this page is intended for general understanding of test results and does not replace medical consultation. Accurate interpretation requires considering other blood markers and individual factors.

Content is based on medical literature and used within the PulseBook analytical system.

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Frequently asked questions

What is the FMN vitamin B2 active form?

FMN is the biologically active form of vitamin B2 derived from riboflavin. It acts as a coenzyme in energy production and cellular respiration. The flavin mononucleotide test helps determine how efficiently the body converts vitamin B2 into this usable form, making it more informative than standard riboflavin measurements.

What is the FMN normal range?

The FMN normal range is typically 10–50 nmol/L in blood. This range reflects adequate vitamin B2 activation for metabolic processes. Values outside this range may indicate deficiency, excessive supplementation, or metabolic dysfunction affecting energy production.

What causes low FMN levels?

Low FMN levels are usually caused by poor diet, alcoholism, malabsorption, or certain medications. These factors reduce riboflavin absorption or conversion into its active form. Low FMN can impair energy metabolism and contribute to symptoms of vitamin B2 deficiency.

Is riboflavin deficiency serious?

Vitamin B2 deficiency can affect energy production, skin health, and red blood cell formation. Over time, it may contribute to anemia, fatigue, and inflammation. The flavin mononucleotide test helps detect functional deficiency early, even when riboflavin intake appears normal.

Which foods are rich in vitamin B2?

Foods rich in B2 include beef liver, eggs, dairy products, almonds, and leafy greens. Some fruits like bananas and avocados contain smaller amounts. A balanced diet helps maintain normal FMN levels and supports metabolic health.

What are vitamin B2 side effects from supplements?

Vitamin B2 supplements are generally safe because excess is excreted in urine. Common harmless effects include bright yellow urine. Very high doses may cause mild digestive discomfort. Elevated FMN levels in a blood test often reflect supplementation rather than toxicity.