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Is it Factor V Leiden, or Factor V Deficiency

From Tiffany Whittle:

Is there a difference between factor V Leiden mutation and factor V deficiency? The reason I ask is that when I donate blood and tell them I am FV Leiden positive they “call” to see if I can donate, since only FV deficiency is in their book. They have told me to always say I am FV deficient so they do not have to call because the blood center will discard plasma for both disorders.

I just had a problem with that because I was taught that there is a difference: no FV Vs a change in the gene code for FV which causes the FV to work overtime. Thanks.

Hi, Tiffany, it is nice to hear from you. I realize that I’ve met you through the Carolinas Clinical Connection and that you are my neighbor over there in South Carolina.

You are absolutely right, and your blood center should know the difference. We laboratory scientists shoot ourselves in the foot by the way we name our assays. Every day someone gets confused about factor V deficiency and factor V Leiden. Often labs receive specimens accompanied by an isolated order for factor V. We always call, because it would be quite unusual to only test for factor V, we are sure they meant factor V Leiden mutation, and that is what they confirm on the phone.

The letter C gets us into even more trouble: protein C deficiency, activated protein C resistance, and C-reactive protein. For the physician or unit personnel who have to write the order, this is a real roll of the dice, unless they are very familiar with the names.

Same for factor X, chromogenic factor X, and the chromogenic anti-Xa heparin assay. Many perfectly intelligent people think this means the letter X, not the Roman numeral X (10). It makes sense.

Whenever we try to improve on lab test names by coming up with a new, more descriptive name, it seems we merely add to the confusion, because now there is just one more name to learn.

There is actually a CDC task force at work right now attempting to sort out laboratory nomenclature. The American Society for Clinical Laboratory Science is deeply involved. They picked out vitamin D to work with, as it turns out there are twenty names for the various members of the vitamin D family, a bigger problem than coag! There is also a commercial project, Logical Observation Identifiers Names and Codes (LOINC®) that is attempting to codify every laboratory assay. The big labs like Quest and LabCorp are starting to use LOINC to try to keep all their test orders straight.

Sorry to be so long-winded. I suggest the next time you go to donate blood, tell them you are activated protein C resistant (APCR positive) instead of factor V Leiden positive. They mean almost the same thing, and maybe APCR is in the donor service database. Despite their instructions, do not say you are factor V deficient, that would be a rare and very serious bleeding disorder. This would cause you to be deferred and identified as hemophilic. I hope this helps.

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