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Common Test-Ordering Errors
Part 5: Overordered Tests

Plasma Thiamin
Serum Folate
Zinc Protoporphyrin (ZPP)


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Thiamin (Vitamin B1)

Slide 6

August 2010

Thiamin diphosphate (also called thiamin pyrophosphate) is the active form of thiamin and is the best measure of thiamin status. Thiamin diphosphate in circulating blood is primarily present in erythrocytes, with <10% in the plasma phase of blood. Thus, testing of serum or plasma doSes not provide a useful result.

HPLC analysis of thiamin diphosphate in whole blood or in erythrocytes is a sensitive, specific, and precise method for determining the nutritional status of thiamin and is a reliable indicator of total body thiamin stores. "Thiamin (Vitamin B1), Whole Blood" is available at Mayo Medical Laboratories. This assay specifically quantitates the active form of vitamin B1 as an indicator of vitamin B1status.

For a good while, we encouraged our customers to order the whole blood thiamin test but when we received orders for plasma thiamin, we forwarded the specimens on to another laboratory. Recently, because of the demonstrated lack of utility of serum and plasma B1 levels, we took this a step further and discontinued forwarding those tests.

(Vitamin B1)


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