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Table 3 Serologic and urinary assays of niacin and its metabolites

From: Pellagrous encephalopathy presenting as alcohol withdrawal delirium: A case series and literature review

  Deficient Low Adequate High
Serum*     
niacin (mg/mL)   <0.5 0.5 − 8.45 >8.45
Urine     
adults (men; and nongravid and 1st trimester women) <0.5 0.5 − 1.59 1.6 − 4.29 ≥4.3
2nd trimester women <0.6 0.6 − 1.99 2 − 4.99 ≥5
3rd trimester women <0.8 0.8 − 2.49 2.5 − 6.49 ≥6.5
2-pyridone/N1-methylnicotinamide <0.5 0.5 − 0.99 1 − 4 >4
  1. *Niacin assays require plasma obtained using a lavender-topped tube with ethylenediaminetetraacetic acid (EDTA). Despite niacin's stability when exposed to light, heat, and humidity [36], laboratories often require that samples be wrapped in foil to protect them from light and freezing immediately [37].
  2. †Urinary assays more accurately assess niacin intake than confirm the presence of niacin deficiency. As such, serum niacin would be appropriate test for laboratory confirmation of niacin deficiency [35].