From the Guidelines
Niacin deficiency is diagnosed through a combination of clinical evaluation, medical history, and laboratory tests, with a strong emphasis on suspicion from at-risk clinical history and presence of signs or symptoms, as recommended by the latest guidelines 1. When diagnosing niacin deficiency, doctors look for characteristic symptoms of pellagra, including:
- Dermatitis
- Diarrhea
- Dementia
- In severe cases, death (the "4 Ds") Blood tests measuring levels of niacin metabolites, particularly N-methylnicotinamide and pyridone in urine, are used to confirm the diagnosis. Low levels of NAD and NADP in red blood cells may also indicate deficiency. A therapeutic trial of niacin supplementation can be diagnostic if symptoms improve after treatment. Risk factors that strengthen suspicion include:
- Malnutrition
- Alcoholism
- Certain medications (like isoniazid)
- Carcinoid syndrome
- Hartnup disease Early diagnosis is crucial as untreated niacin deficiency can lead to permanent neurological damage, so physicians should consider this condition in patients with unexplained skin lesions, gastrointestinal problems, or neurological symptoms, especially when combined with poor nutritional status, as supported by the latest guideline 1. The espen micronutrient guideline recommends providing additional amounts of niacin when there is suspicion of deficiency from at-risk clinical history and/or presence of signs or symptoms, with a strong consensus of 95% 1.
From the Research
Diagnosis of Niacin Deficiency
Niacin deficiency can be diagnosed through various methods, including:
- Biochemical markers such as urinary and blood levels of niacin metabolites 2
- Measurement of whole blood NAD and NADP concentrations, although this method may not be reliable 3
- Erythrocyte niacin coenzymes and plasma tryptophan levels 4
- Urinary excretion of niacin and its metabolites, which correlates with dietary intakes 5
Biochemical Markers
Biochemical markers such as N1-methylnicotinamide (NMN) and N1-methyl-2-pyridone-5-carboxamide (2-pyr) in urine and plasma can be used to assess niacin status 2. A urine excretion of less than 1.2 mg/d of either NMN or 2-pyr can indicate niacin deficiency.
Urinary Excretion
Urinary excretion of niacin and its metabolites can be used as a measure of niacin intake 5. The concentrations of 2-PYR and 1-MN in urine, expressed relative to creatinine or osmolality, can be used to diagnose niacin deficiency 3.
Blood Tests
Whole blood NAD and NADP concentrations can be measured, but this method may not be reliable for diagnosing niacin deficiency 3. Erythrocyte NAD levels can serve as a sensitive indicator for the assessment of niacin status, and a niacin index (the ratio of erythrocyte NAD to NADP) below 1.0 may identify subjects at risk of developing a niacin deficiency 4.