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Common Test-Ordering Errors
Part 1: Misordered Tests

1,25-Dihydroxyvitamin D
PTH-related Peptide
Uroporphyrinogen III Synthase


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Vitamin D Pathway

Slide 11

April 2010

One reason that 1,25-Dihydroxyvitamin Ds are misordered may be that the individuals ordering vitamin D tests remember this pathway and assume that the end product, the biologically active form of vitamin D (1,25-dihydroxy vitamin D), is what you want to measure. But, that is not the case.

In most situations, when screening or monitoring for vitamin D deficiency or excess, it is the body stores that are the concern, and the correct test for that use is 25-Hydroxyvitamin D. 1,25-Dihydroxyvitamin D is an appropriate test, in certain situations. Recalling that the kidney is the site of synthesis of the active hormone, 1,25-Dihydroxyvitamin D testing plays a legitimate role in patients with renal failure. It is also a second-order test in the assessment of vitamin D status, especially for patients with uncommon disorders such as those with hypercalcemia and suppressed PTH, and patients with vitamin D-dependent rickets due to hereditary deficiency of renal 1-alpha hydroxylase or due to end-organ resistance to 1,25-dihydroxyvitamin D. We believe these indications together make up only about 20% of the 1,25-dihydroxyvitamin D orders we receive, with the remaining being ordered incorrectly.

Vitamin D Pathway


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