Plasma Pyridoxal-5'-Phosphate Level of 91 nmol/L: Normal and No Supplementation Needed
A plasma PLP level of 91 nmol/L is well within the normal range (20-200 nmol/L), and vitamin B6 supplementation is not indicated for an asymptomatic adult without risk factors. 1
Understanding Your Result
Your PLP level of 91 nmol/L falls comfortably in the middle of the normal reference range established by ESPEN guidelines. 1 This level indicates adequate vitamin B6 status, as sufficiency is defined as plasma PLP above 30 nmol/L. 2
- The normal range for plasma PLP is 20-200 nmol/L (5-50 mg/L). 1
- Your level of 91 nmol/L represents optimal vitamin B6 status, well above the sufficiency threshold of 30 nmol/L. 2
- Deficiency is defined as PLP below 20 nmol/L, and insufficiency as 20-30 nmol/L. 3
Why Supplementation Is Not Recommended
Supplementing when your levels are already normal is unnecessary and potentially harmful. 4 The upper safe limit for long-term supplementation is 100 mg/day, with doses at or above this level associated with serious neurological complications. 1
- Excessive vitamin B6 causes sensory neuropathy with ataxia, loss of deep tendon reflexes, impaired sensation, and dermatologic lesions. 1
- Even doses as low as 100 mg/day taken long-term have been linked to Lhermitte signs (electrical shock sensations). 1
- Neurotoxicity typically develops when plasma PLP levels exceed 100 nmol/L, which can occur with daily supraphysiologic dosing. 2
- Some nerve damage from B6 toxicity may persist even after discontinuation of supplementation. 5
When Supplementation Would Be Indicated
You would only need vitamin B6 supplementation if you develop specific risk factors or clinical deficiency. 4
Risk factors requiring supplementation include: 1, 4
- Chronic kidney disease, particularly dialysis patients (who may need 10 mg daily)
- Chronic alcoholism with documented deficiency
- Medications that interfere with B6: isoniazid, penicillamine, anti-cancer drugs, corticosteroids, or anticonvulsants
- Critical illness or post-operative states
- Pregnancy (requirements increase to 2 mg/day)
Clinical signs of true deficiency include: 1, 4
- Seborrheic dermatitis with cheilosis and glossitis
- Microcytic anemia
- Epileptiform convulsions
- Confusion or depression
- Angular stomatitis
Dietary Maintenance
The recommended daily allowance for adults aged 14-70 years is only 1.3-1.7 mg/day, easily obtained through diet. 1
- Vitamin B6 is found in meat, whole grains, fortified cereals, and potatoes. 1
- Your body has no stores of pyridoxine, so diet is the only natural source. 1
- PLP levels respond to dietary intake within 6-10 days, reflecting liver stores. 1
Common Pitfall to Avoid
The most important pitfall is unnecessary supplementation based on misunderstanding normal laboratory values. 4 A level at the lower end of normal does not constitute deficiency—the threshold for clinical deficiency is below the normal range, not at its lower boundary. 4 Your level of 91 nmol/L is not at the lower end; it is solidly mid-range and optimal.
Monitoring Recommendations
No follow-up testing is indicated for a healthy adult with normal PLP levels and no risk factors. 4 You would only need repeat testing if you develop conditions that increase B6 requirements (kidney disease, pregnancy), if your dietary intake becomes severely restricted, or if you develop clinical symptoms of deficiency. 4