Hey Pattik,
Excellent question and one that has baffled many CHers (including some of their PCPs/neurologists) when they read assay results of their 25(OH)D3 serum concentrations from different labs. The reason for the differential in 25(OH)D3 assay results from different medical diagnostic labs is due to the different assay methods they use.
There are four different automated assay methods for serum 25(OH)D3. They include Chemiluminescence Immunoassays (CLIA), Radioimmunoassy (RIA), High Performance Liquid Chromatography (HPLC) and the Liquid Chromatography-tandem Mass Spectrometry (LC-MS/MS) methods. All four will produce different 25(OH)D3 serum concentration measurements from the same blood draw.
The two most common automated systems used to assay 25(OH)D3 serum concentrations are the DiaSorin LIAISON RIA and LC-MS/MS assay. 25(OH)D3 serum concentrations measured by the LC-MS/MS assay method are consistently much higher than those measured by the DiaSorin LIAISON RIA assay method, with a mean difference of 12.9 ng/ml. The bottom line lesson learned here is stick with the same diagnostic lab for your 25(OH)D3 assays.
The first assay of my serum 25(OH)D3 at my PCP's office was done by LabCorp. They used the DiaSorin LIAISON RIA assay method. I had already obtained a home blood spot test kit assay from Grassrootshealth a week earlier at 130 ng/mL. This blood spot 25(OH)D3 assay uses the LC-MS/MS assay method so I expected the 25(OH)D3 assay from LabCorp to be at a slightly lower serum concentration, but was surprised when it came back at 110 ng/mL, 20 ng/mL lower.
My PCP went into the panic mode with his knickers in a wad and told me to stop taking vitamin D3 immediately as my 25(OH)D3 was over 100 ng/mL. I asked if they had done the calcium and PTH labs as I had asked and the answer was no.
I had been loading vitamin D3 at the time to get through a heavy pollen fall that had triggered an allergic reaction a year earlier with a return of my CH at a 25(OH)D3 serum concentration of 90 ng/mL. I knew from previous 25(OH)D3 burn down tests I could coast without any vitamin D3 for a while so stopped taking vitamin D3 for 30 CH pain free days then went back to my PCP for another set of labs only this time I made sure the Rx script called for serum 25(OH)D3, calcium and PTH. I also had my PCP cut an identical script for these same lab tests at the Quest Diagnostics collection facility across the parking lot from my PCP's office.
I had the blood draw at my PCPs office by LabCorp then walked across the parking lot for another blood draw at Quest Diagnostics 5 minutes later. When LabCorp posted my lab results, my 25(OH)D3 assay. was 97 ng/mL and my PCP was all smiles. When he downloaded the results from Quest Diagnostics, my 25(OH)D3 assay was 117 ng/mL. My PCP's smile turned to a frown as he looked at the results in dismay. I explained the 20 ng/mL differential was due to the different assay methods.
My PCP remarked, that he had no idea the differential could be that high between the two assay methods, but was still concerned my 25(OH)D3 was still too high. That's when I asked for the serum calcium assay and told him if it was well within its normal reference range, there's no hypercalcemia therefor, no vitamin D3 intoxication/toxicity so no need to stop taking vitamin D3. The serum calcium assay was well within its normal reference range.
Long story made short, after educating my PCP on lab tests for serum 25(OH)D3, calcium and PTH and their interpretation, he now has no problem with my 25(OH)D3 being well above 100 ng/mL at a mean of 150 ng/mL and as high as 188 ng/mL as long as my serum calcium remains within its normal reference range. As you'll see in the following 3-year chart of my labs for 25(OH)D3, calcium and PTH, it has.
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That said, I can see why the 109 vs 134 discrepancy you've reported is so perplexing. You're correct in expecting a 25(OH)D3 assay less than 109 ng/mL after 8 weeks taking 3000 IU/day vitamin D3. I would have the same expectation.
The reasons for this discrepancy can include, but are not limited to, the difference between automated 25(OH)D3 assay systems as discussed above, errors in assay measurements (they do occur), changes in immune system activity that change the rate of 25(OH)D3 consumption, changes in the rate of vitamin D3 hydroxylation to 25(OH)D3 and changes in the rate of 24-Hydroxylation which takes vitamin D3 and 25(OH)D3 out of the bloodstream.
At this point, I doubt we can make a determination of why this discrepancy occurred. What I can say is the only real value of the 25(OH)D3 assay is its relationship to your CH status that I call the 25(OH)D3 serum concentration CH Threshold. Moreover, the 25(OH)D3 serum concentration cannot and should not be used as an indication of vitamin D3 intoxication/toxicity. Only the calcium serum concentration should be used to make this determination.
The more important assays are serum calcium and PTH as they provide an important indication of calcium homeostasis (how the body controls serum calcium in a very narrow range). In short, as long as you're CH pain free and your serum calcium remains within its normal reference range, whatever vitamin D3 dose you're taking is safe and the actual 25(OH)D3 serum concentration is meaningless.
In response to which assay method is more accurate? the LC-MS/MS has pretty much become the gold standard.
Now back to you thinking your serum 25(OH)D3 assay is too high and that you want to lower the vitamin D3 maintenance dose. My first question is What was your calcium serum concentration? From my experience and reports from many other CHers, trying to lower 25(OH)D3 serum concentration with lower doses of vitamin D3 while CH pain free with normal calcium serum concentrations is not wise. Here's why.
We all have a 25(OH)D3 cluster headache threshold serum concentration. At or below that 25(OH)D3 serum concentration, the CH beast jumps ugly. When our actual 25(OH)D3 serum concentration is higher than this threshold, we remain CH pain free.
I developed the anti-inflammatory regimen based on a vitamin D3 dose of 10,000 IU/day knowing there would be variations in the 25(OH)D3 response and that most adults taking this much vitamin D3 would have a 25(OH)D3 serum concentration higher than their CH threshold.
Baseline 25(OH)D3 assays from the online survey of 313 CHers with active bouts of CH before start of regimen are illustrated in the following normal distribution plot. It indicates a maximum 25(OH)D3 serum concentration of 47 ng/mL (117.5 nmol/L). Accordingly, we can use this 25(OH)D3 serum concentration as a reasonable estimate of the lower boundary of the CH threshold serum concentration range. I should point out that a CHer found his 25(OH)D3 CH threshold serum concentration was 162 ng/mL working with his PCP and having frequent 25(OH)D3 assays.
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The following normal distribution chart of 25(OH)D3 lab results reported in the online survey of 257 CHers reporting a favorable CH response ≥ 30 days after starting the anti-inflammatory regimen is a classic example of variations in the 25(OH)D3 response to a vitamin D3 dose of 10,000 IU/day between individual CHers.
If you consider the 1 sigma (Standard Deviation) of 30 ng/mL about the mean of 80 ng/mL, you have 66% of CHers taking 10,000 IU/day vitamin D3 with a 25(OH)D3 serum concentration between 50 ng/mL and 120 ng/mL.
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Look at a 25(OH)D3 serum concentration above the CH threshold as a safety margin or head space to guard against fluctuations in the CH threshold and actual 25(OH)D3 serum concentrations as they both can and do fluctuate. The following notional graphic illustrates the CH threshold 25(OH)D3 serum concentration in red and the actual 25(OH)D3 serum concentration in green.
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As depicted, there are always fluctuations in both serum concentrations and theses fluctuations are highest during an immune system response. The immune system response can be due to an allergic reaction to toxins, pollen, mold spores or diet, other Rx medications, infections (bacterial, viral and fungal), trauma and surgery. If these two 25(OH)D3 serum concentrations meet or overlap, the CH beast jumps ugly. The greater the overlap, the worse the CH beast jumps ugly.
Sooo... the bottom line suggestion follows. If you remain CH pain free at a vitamin D3 maintenance dose of 10,000 IU/day and your calcium serum concentration remains within its normal reference range, declare success and don't change a thing no matter where your 25(OH)D3 serum concentration plots out. In short, stick with the age old addage/aphorism - If it's not broken, don't try to fix it.
Take care and please keep us posted.
V/R, Batch