What are VB1 (Vitamin B1), VB2 (Vitamin B2), and VB3 (Vitamin B3) urine tests and their accuracy?

VB1, VB2, and VB3 Urine Tests and Their Accuracy

VB1, VB2, and VB3 urine tests measure vitamin B1 (thiamine), vitamin B2 (riboflavin), and vitamin B3 (niacin) metabolites in urine to assess vitamin status, with urinary output being the only universally accepted method for vitamin B3 assessment, though accuracy is limited by various factors including timing of collection and individual metabolic differences. 1

Vitamin B1 (Thiamine) Urine Testing

• Urinary output of vitamin B1 is used to assess thiamine status, though the association between vitamin status and urinary output can be aberrant, particularly in elderly populations 1
• The UK dietary recommendations for vitamin B1 (0.9 mg/day for men, 0.8 mg/day for women aged ≥50 years) were partly determined using urinary output measures 1
• Urine loading tests can detect thiamine deficiency, as demonstrated in an investigation where workers with edema showed urinary VB1 concentrations far below normal values 2
• Limitations of accuracy:
  • Urinary output of thiamine does not always correlate with actual vitamin B1 status, with one study showing biochemical deficiency in over 50% of subjects despite intake exceeding guideline requirements 1
  • Timing of collection and individual metabolic differences can affect results 1

Vitamin B2 (Riboflavin) Urine Testing

• Urinary riboflavin excretion can be measured to assess vitamin B2 status, though this is less common than erythrocyte glutathione reductase activation coefficient (EGRAC) testing 3
• Limitations of accuracy:
  • Urinary excretion of riboflavin is affected by recent dietary intake, making it less reliable for assessing long-term status 1
  • Factors such as gender, age, education level, alcohol consumption, and smoking can affect vitamin B2 intake but may not consistently affect biochemical indices of nutritional status 3

Vitamin B3 (Niacin) Urine Testing

• Urinary output of N-methyl-nicotinamide and its downstream metabolite methyl-pyridone carboxamide represents the only universally accepted method for assessing vitamin B3 status 1
• The UK RNI for vitamin B3 (16 mg/day for men, 12 mg/day for women aged ≥50 years) is based on urinary output of these metabolites 1
• Limitations of accuracy:
  • Intake data frequently do not correlate with biochemical determinants of status, including urinary metabolites 1
  • Genetic variability can affect the relationship between intake and urinary excretion 1
  • Bioavailability of vitamin B3 from food sources (particularly cereal grains) can be reduced by glycosides that bond with the vitamin 1

Alternative Testing Methods with Better Accuracy

• For vitamin B1 (thiamine):

  • Erythrocyte transketolase activity (TKA) is more accurate than urine testing 1, 4
  • TKA with thiamine pyrophosphate (TPP) effect >14% indicates deficiency, though cut-off points vary (>1.15 to >1.25) 1, 4

• For vitamin B2 (riboflavin):

  • Erythrocyte glutathione reductase activation coefficient is the preferred method 4, 3
  • Upper limit for stimulated enzyme activity in control subjects is 63% 4

• For vitamin B3 (niacin):

  • No clearly superior alternative to urine testing is established in guidelines 1

Clinical Considerations

• Deficiencies of these vitamins can cause significant health problems:

  • Vitamin B1 deficiency can lead to Wernicke encephalopathy, which can be fatal but treatable 4
  • Vitamin B1 and B2 deficiencies correlate with cerebellar and brainstem lesions, particularly in alcoholics 5
  • Vitamin B3 deficiency can lead to pellagra 1

• High-risk populations for deficiencies include:

  • Critically ill patients (12.5% thiamine deficient in one study) 4
  • Patients receiving chemotherapy 4
  • Alcoholics (31% thiamine deficient, 22% riboflavin deficient in one study) 5
  • Elderly populations, with prevalence of vitamin B1 deficiency between 10-47% 1

Pitfalls and Caveats

• Urinary tests for these vitamins should not be used in isolation for diagnosis due to their limitations 1
• Certain medications (colchicine, H2 receptor antagonists, metformin, phenobarbital, pregabalin, primidone) can contribute to vitamin B deficiencies and affect test results 6
• In the presence of inflammation, intracellular measurements appear more reliable than plasma or urine measurements 1
• Storage, cooking methods, and co-ingestion of substances like alcohol, sulfites, tannins, and coffee can reduce vitamin content and bioavailability, affecting test results 1