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Common Test-Ordering Errors
Part 5: Overordered Tests

Plasma Thiamin
Serum Folate
Zinc Protoporphyrin (ZPP)



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Folate—Serum and RBC

Slide 7

August 2010

Serum folate is another overordered vitamin test. Folate is a B vitamin and, along with vitamin B12, is required for normal red blood cell maturation. Deficiency of either of these nutrients causes macrocytic anemia.

While laboratory testing for patients with macrocytic anemia typically begins with measurement of serum folate and vitamin B12 concentrations, folate levels are relatively poor predictors of total body folate stores. Serum folate is neither sensitive nor specific:

  • Serum folate levels typically fall within a few days after dietary folate intake is reduced and may be low even in the presence of adequate tissue stores. Alcohol intake and medications may cause similar changes.
  • Conversely, serum folate concentration may rapidly rise to a normal level after just 1 balanced meal, and may be normal despite the presence of low tissue stores.

Red blood cell folate concentration is less subject to short-term dietary changes and is thus considered more reliable, but that test also has sensitivity and specificity problems.

Folate—Serum and RBC

 


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