☀️ Vitamin D That Won't Come Up
For everyone · 5 markers · $123.30
with code CAMERON $137.00
You have been supplementing vitamin D for months and the number has barely moved. Or you take vitamin D and calcium and still get cramps, palpitations or low mood. Also for anyone whose calcium came back at the top of the range or just above it, which is a finding almost nobody follows up.
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All 5 markers load into your cart in one click. No doctor's visit, drawn at any Quest location in the US, results by email in about two weeks. Code CAMERON applies automatically.
Add all 5 markers — $123.30 → Open the full Bloodwork Vault →Why this panel
Vitamin D does not work alone. Every enzymatic step that turns the vitamin you swallow into the hormone your body uses is magnesium-dependent, as is the protein that transports it, and so is the parathyroid gland that regulates the whole system. If magnesium is low, vitamin D supplementation can run for a year without the 25-OH number moving much — and taking more vitamin D consumes more magnesium, which makes the problem worse. This panel measures the vitamin, both magnesium fractions, and the hormone that sits between them.
What this panel can settle, and by what logic
Five markers, and the value is that they are read as one system rather than as five results. Vitamin D, magnesium and parathyroid hormone regulate each other, so any one of them measured alone can be normal while the system is not working.
- Magnesium, RBC and Magnesium (Serum) beside Vitamin D (25-Hydroxy) answer the question people actually arrive with. The enzymatic steps that convert cholecalciferol to 25-hydroxyvitamin D and then to the active hormone are magnesium-dependent hydroxylases, and the binding protein that transports the result is magnesium-dependent too, so magnesium status constrains what a vitamin D dose can achieve Matias 2023. In a large adult cohort with a high prevalence of vitamin D deficiency, magnesium and vitamin D status were measurably associated Zittermann 2024.
- Two magnesium fractions rather than one, on purpose. Serum magnesium is tightly defended and is normal in a large share of genuine depletion, which is the central complaint about it in the laboratory literature Ab Rahim 2023Fiorentini 2021. It is also what defines the clinical syndrome and what a clinician will act on. Red cell magnesium reads status over months instead. At $13 for the serum value the argument for choosing between them is weak Henriksen 2023.
- Parathyroid Hormone & Calcium is the marker that turns this from a supplement check into a workup. Read against calcium, PTH separates three situations that look identical from a vitamin D result alone: simple vitamin D deficiency driving a high PTH with normal calcium, magnesium depletion producing a low or inappropriately normal PTH, and primary hyperparathyroidism where calcium is raised and PTH has failed to switch off Shaker 2023.
- Comprehensive Metabolic Panel (CMP) is not filler here. Calcium is carried on albumin, so a calcium result without an albumin is not a calcium result, and kidney function changes the interpretation of every other number on the list.
The discrimination that only exists because all five are on one report: a parathyroid hormone inside the reference range is not automatically normal. When calcium is high, PTH should be suppressed. A mid-range PTH beside a high-normal calcium is one of the most commonly missed endocrine findings there is, and it is visible only when both numbers are on the same page Shaker 2023.
What it cannot settle, and what would
It cannot measure your bone. Vitamin D, PTH and calcium describe the system that maintains the skeleton; they do not say what state the skeleton is in. If the real question is fracture risk, the test is a DEXA scan and this panel is the workup that accompanies it rather than a substitute.
It cannot confirm primary hyperparathyroidism on its own. The eucalcemic and normocalcemic presentations require repeated calcium measurements, a vitamin D level that is already adequate, and exclusion of the secondary causes before the diagnosis can be made Shaker 2023. What the panel does is identify the pattern that makes that sequence worth starting, and it is a sequence run by a clinician.
Neither magnesium fraction is a gold standard. Total body magnesium is mostly intracellular and mostly in bone, and every practical blood measure is a proxy of debated quality Ab Rahim 2023Fiorentini 2021. Two proxies that agree are much stronger than either alone; two that disagree mean the question is still open.
And it cannot tell you why your vitamin D is low. Low sun exposure, obesity sequestering vitamin D in fat, malabsorption and simple non-adherence all produce the same number, and the first distinction to make is whether the supplement is actually being taken.
Draw conditions that decide whether the money is wasted
Four conditions. The first two decide whether the PTH result can be used at all.
- Morning, fasted. Parathyroid hormone and calcium both follow a daily rhythm, so an afternoon PTH cannot be compared with a morning reference interval or with a previous morning value Shaker 2023. This is the single most wasteful mistake available on this panel, because PTH is $75 of the $137.
- No biotin for 72 hours. Hair, skin and nail products carry 5,000 to 10,000 mcg, and biotin at those doses interferes with streptavidin-based immunoassays including the ones used for PTH and for 25-hydroxyvitamin D Li 2020. A falsely abnormal PTH here starts an entire endocrine investigation.
- No magnesium supplement and no vitamin D for 24 hours. Both produce a short-lived rise that reports the dose rather than the status Fiorentini 2021.
- Not during or immediately after an illness. Albumin falls with inflammation and calcium is read against albumin, so a sick-day draw produces a low calcium that means nothing.
How you would know it answered your question, and what each pattern means next
Four patterns. One of them does not wait.
- Low Vitamin D (25-Hydroxy), high PTH with normal calcium, normal magnesium: ordinary vitamin D deficiency with an appropriate parathyroid response. Supplement and retest Vitamin D (25-Hydroxy) at 12 weeks, which is roughly three half-lives of 25-hydroxyvitamin D and the point at which a new steady state has been reached. PTH should fall with it.
- Vitamin D (25-Hydroxy) that has not moved after 12 weeks of consistent dosing, with a low or low-normal Magnesium, RBC: replete magnesium first and retest both at 12 weeks Matias 2023Zittermann 2024. Adding more vitamin D to a magnesium-depleted system consumes more magnesium and makes the underlying problem worse.
- Calcium above the reference range with a PTH that is not suppressed: this is the result that needs a doctor rather than a supplement change, whatever the vitamin D says Shaker 2023. Repeat calcium and PTH within weeks, not months.
- Low calcium with a low or inappropriately normal PTH and a low Magnesium (Serum): magnesium is blocking both the release of PTH and the response to it. Correcting the magnesium is what corrects the calcium, and calcium supplements alone will not Ab Rahim 2023.
The finding that ends the question: a 25-hydroxyvitamin D that rises as expected on a known dose, with a PTH that falls alongside it, means the system is working and an annual Vitamin D (25-Hydroxy) is enough.
Sources read for these sections
- Matias P, et al. Hypomagnesemia: a potential underlooked cause of persistent vitamin D deficiency in chronic kidney disease. Clinical Kidney Journal 2023 · PMID 37915933
- Zittermann A, et al. Association between magnesium and vitamin D status in adults with high prevalence of vitamin D deficiency and insufficiency. European Journal of Nutrition 2024 · PMID 39680162
- Shaker JL, Wermers RA. The Eucalcemic Patient With Elevated Parathyroid Hormone Levels. Journal of the Endocrine Society 2023 · PMID 36793479
- Ab Rahim SN, et al. The Laboratory and Clinical Perspectives of Magnesium Imbalance. Cureus 2023 · PMID 38045630
- Fiorentini D, et al. Magnesium: Biochemistry, Nutrition, Detection, and Social Impact of Diseases Linked to Its Deficiency. Nutrients 2021 · PMID 33808247
- Henriksen C, et al. Magnesium: a scoping review for Nordic Nutrition Recommendations 2023. Food and Nutrition Research 2023 · PMID 38084152
- Li D, Ferguson A, Cervinski MA, Lynch KL, Kyle PB. AACC Guidance Document on Biotin Interference in Laboratory Tests. J Appl Lab Med 2020 · PMID 32445355
The 5 markers — and why each one is here
The storage form and the number everyone tracks. It is the question, not the answer
Red cell magnesium reflects status over months and is the better test of the two
Serum magnesium is the number a clinician acts on and defines the clinical syndrome. Cheap, and not interchangeable with the red cell value
PTH and calcium reported together — the only way to know whether a PTH is appropriate
Albumin, kidney function and electrolytes. Calcium cannot be interpreted without albumin
What this panel is ordered to decide
A panel is a set of numbers until it settles something. These are the decisions this one feeds — each links the pathway it belongs to, what that pathway claims, and what its test list is read for.
If you cannot fall asleep, check whether something is keeping you awake before you sedate on top of it. High evening cortisol and an overactive thyroid both do this.
A multivitamin is a hedge against gaps you haven't measured. This panel tells you which gaps are real — and RBC values beat serum for zinc, magnesium and folate, because serum is defended at the expense of tissue.
Related panels
A panel gives you numbers. Skool is where they get read — 103 marker breakdowns with the optimal range rather than just the lab range, 42 evidence-graded protocols, and me answering questions daily. $10/mo, cancel anytime.
Join Skool — $10/mo →Frequently asked questions
5 markers: Vitamin D (25-Hydroxy), Magnesium, RBC, Magnesium, Parathyroid Hormone & Calcium, Comprehensive Metabolic Panel (CMP).
$137.00 before discount, $123.30 with code CAMERON applied automatically. Individual markers add a one-time $10 draw fee. Ordered through Marek Diagnostics and drawn at any Quest Diagnostics location in the US.
No. These are ordered direct-to-consumer through Marek Diagnostics — you order online, walk into a Quest location, and results are emailed to you in about two weeks. No physician visit or insurance required. Not available in NY, NJ or RI.
Fast 9-12 hours and draw in the morning — PTH and calcium both have a daily rhythm and afternoon values are not comparable to morning ones. Take no magnesium supplement and no vitamin D for 24 hours before the draw. Note biotin: at the 5,000-10,000 mcg doses sold for hair and nails it interferes with several of the immunoassays used here, so leave 72 hours clear. If you have had a recent illness, wait — albumin falls with inflammation, and calcium has to be read against albumin.
Simple deficiency: low vitamin D, high PTH, normal calcium, normal magnesium — supplement and retest at 12 weeks. Magnesium-limited: low or low-normal magnesium (especially red cell magnesium) with a vitamin D that will not rise despite dosing. Repletion of magnesium first is what makes the vitamin D respond. Calcium above the reference range with a PTH that is not suppressed is the one result on this panel that needs a doctor rather than a supplement change, whatever the vitamin D says.
Where this goes next
The pages here are the frameworks. The protocols — the dosing, the order to correct things in, the week-by-week schedule and what to retest — are inside Skool.