Vitamin D deficiency is rampant
not just in the U.S., but worldwide, and research into vitamin
D status and its effects on your health has grown tremendously
in the past couple of years, showing that previously recommended
levels are insufficient to reap any major health benefits.
This has led to a surge in vitamin D testing, with labs like
Quest doing some 500,000 tests per month!
Unfortunately, recent developments in 2008 have made it clear
that there are irregularities in the values obtained from
the different testing methods. Although results from any of
the three commonly used assays may be analytically accurate,
they might not be clinically accurate, which is, ultimately,
First -- Order the Correct Test
First of all, it is very important that your physician orders
the correct test as there are two vitamin D tests -- 1,25(OH)D,
25(OH)D is the better marker of overall D status. It is this
marker that is most strongly associated with overall health.
The correct test is 25(OH)D, also called 25-hydroxyvitamin
Second Measure Your Results Against Optimal Values
Please note the difference between normal and optimal. You
don't want to be average here; you want to be optimally healthy.
These optimal values have been confirmed by more recent studies
into vitamin D status and its effects on health and reduced
Optimal 25-hydroxyvitamin D values are:
45-50 ng/ml or
Normal 25-hydroxyvitamin D lab values are:
Your vitamin D level should NEVER be below 32 ng/ml. Any
levels below 20 ng/ml are considered serious deficiency states
and will increase your risk of breast- and prostate cancer,
and autoimmune diseases like MS and rheumatoid arthritis.
If you have the above test performed, please recognize that
many commercial labs are using the older, dated reference
ranges. The above values are the most recent ones based on
large-scale clinical research findings.
Third -- Make Sure Your Lab Uses the STANDARD Assay
There are a number of different companies that have approval
to perform vitamin D testing, but the gold standard is DiaSorin.
Their radioimmunoassay (RIA) method for measuring total vitamin
D levels has become the gold standard, not because its
more accurate than the others, but because its the one
used in almost every major vitamin D study, on which the recommended
blood levels for clinical efficacy are based.
Therefore, in order for any other testing method to offer
clinically relevant results, the test values must agree with
DiaSorin RIA results, since those were used to establish the
Vitamin D status is measured by looking at blood levels of
25-hydroxyvitamin D3. There are three common methods used
for measuring vitamin D3:
1. LC-MS/MS -- This test measures 25-hydroxyvitamin D2 and
2. RIA (DiaSorin) -- Developed in 1985, it accurately measures
total 25-hydroxyvitamin D (It does not separate D2 and D3)
3. Liaison (DiaSorin) -- a more recently developed automated
immunoassay by DiaSorin that has largely replaced the RIA
The LC-MS/MS (liquid chromotatography-mass spectrometry)
method is the preferred method for many labs, including the
Mayo Clinic, Quest Labs, Esoterix, ZRT, and others, while
Liaison is favored by other testing labs like LabCorp.
Since the DiaSorin assay (RIA) was used in the major clinical
studies that led to the recommended vitamin D levels, any
lab using the LC-MS/MS method need to make sure their test
correlate with the RIA test values in order to accurately
determine your vitamin D status.
WARNING: Your Lab Can Give You the WRONG Results!
The test Quest uses, while analytically accurate, gives vitamin
D values that are consistently about 25-40 percent higher
than the DiaSorin assay.
What does this mean?
If you are using Quest labs you are getting FALSE reassurances
that your levels are accurate and may even stop or discontinue
treatment thinking that you are in the toxic range when you
still need more vitamin D.
Some labs, such as ZRT and the Mayo Clinic, have recognized
the severity of this problem and have already calibrated their
LC-MS/MS results against the DiaSorin RIA values -- in order
to be clinically applicable -- whereas Quest has failed to
This is a serious problem since Quest probably runs the most
vitamin D assays of any lab in the U.S.
Which Lab Should You Use?
The single biggest concern in this area is Quest Labs as
their lab is reporting results as much as 40 percent higher
than those found with the DiaSorin assay. That means, if you
are seeking to obtain levels similar to those that have been
confirmed optimal in the scientific literature, you will be
falsely reassured by their test results.
At this point in time Quest has NOT recalibrated their test
values to be aligned with DiaSorin, and it appears unlikely
that they will do so anytime in the near future. Making matters
worse, Quest is currently doing over 500,000 tests a month
-- much of this increase has occurred over the past year --
and the consistent reports obtained from the field is that
many split samples being sent to them are coming back widely
different, indicating a lack of consistency and quality.
The LC-MS/MS is clearly a highly accurate test, but only
in the hands of experienced technicians who have the time
to do the test properly, and only if its calibrated
against the RIA.
Liaison, which is a more recently developed DiaSorin test
that renders clinically accurate results, is also a much more
accurate testing method for high volume throughput of tests,
and does not depend as much on lab technicians expertise.
LabCorp uses this method, which makes them better able to
handle large volumes of tests without sacrificing clinical
accuracy or worrying about the qualifications of the staff.
Additionally the charge for the Lab Corp test should be less
than half of that of the Quest test.
For all these reasons it is now strongly recommend to use
LabCorp for these reasons until Quest can guarantee accurate,