What is calcium?
Your body contains about a kilo of calcium, and more than ninety-nine percent of it sits in your bones and teeth. The small part in your blood is the working stock: nerve cells fire with it, muscle fibres contract with it, your heart keeps its rhythm with it and your blood clots with it. Your body holds that part within a narrow band, and it uses your bones as reserve. If the calcium in your blood falls, your parathyroid glands release PTH, which takes calcium from the bones, makes the kidneys hold on to calcium and activates vitamin D so the gut absorbs more. If it rises, the PTH stops and the kidneys excrete the surplus. That is why the calcium in your blood says little about how much calcium you eat: with too little calcium in the diet the blood value stays normal and your bones pay the bill. What does shift the blood value is the regulating loop itself, the parathyroid glands, vitamin D and the kidneys, and the protein the calcium is bound to. About half the calcium in your blood travels bound to albumin. A low albumin gives a low total calcium while the free, working part is normal, and that is the most common reason for a low value. Your report shows calcium in mmol/L. Normal from age 19 is about 2.20 to 2.55 mmol/L, where the labs overlap, one of the narrowest bands on this site. Below 1.80 mmol/L and above 3.00 mmol/L the lab phones the requester the same day.
Why is calcium relevant?
Calcium is a value with a quiet lower end and a sharp upper end. A slightly lowered total calcium is usually a low albumin or a vitamin D deficiency, and the latter is very common in the Netherlands, with little sun from October to April: the gut then absorbs too little calcium, PTH takes it from the bones and the blood value stays just up at the cost of bone density. Anyone who tops up vitamin D, eats enough calcium and loads their bones with strength training and walking keeps the regulating loop at rest and the bones strong. The upper end is the side to take seriously, even without symptoms. A high calcium in someone who feels well, often found by chance, is usually a parathyroid gland releasing too much PTH; that slowly wears down the bones, gives kidney stones and tiredness, and is curable with a small operation. A high calcium in someone who is ill, with thirst, passing a lot of urine, confusion or bone pain, can be a malignancy releasing calcium from the bones, and that should be investigated the same week. Dehydration and a tight tourniquet also lift the value, which is why a repeat with a calm draw is the first step with a high value that does not fit you. And calcium is a value you read with its neighbours. Albumin says whether the total can be trusted, PTH says whether the parathyroid glands are the driver, vitamin D says whether the gut can absorb enough, and creatinine says whether the kidneys are involved. Without those four a calcium value is half an answer.
Calcium reference ranges
What counts beside the number:
- Albumin from the same draw, because half the calcium is bound to it and a low albumin gives a low total without a deficiency
- PTH with every deviating value, because that says whether the parathyroid glands are the driver
- Vitamin D and magnesium with a low value, the two most common reasons
- Creatinine and the eGFR, because kidneys that work less lower calcium
- How the draw went and how much you had drunk, because congestion and dehydration lift the value
- Whether you take calcium tablets, vitamin D, thiazide diuretics or lithium
About half the calcium in your blood circulates free and the other half is bound to protein, almost all of it albumin. A low albumin therefore lowers the total without changing the working part; if your albumin is low, read corrected calcium or free calcium. A tight tourniquet, a long clenched fist and dehydration lift the total; a calm, well-hydrated repeat gives your true value.
What Dutch labs actually use
Calcium is one of the most tightly regulated values on this site, and it shows: the four labs sit close together. Even so the ceiling differs by 0.10, and it is that side which counts. Star-shl and Clinical Diagnostics use 2.65, Unilabs and Certe 2.55. Someone at 2.60 mmol/L is therefore normal at two labs and raised at the other two, while a raised calcium is the side you take seriously.
2.20 – 2.55mmol/L
Between 2.15 and 2.20 and between 2.55 and 2.65 it depends on the lab, because each sets its limits on its own method and population. Above 2.65 every lab calls it abnormal.
every lab calls 2.20 – 2.55 mmol/L normal. Between 2.15 and 2.20 and between 2.55 and 2.65 it depends on the lab.
Every age, per lab
| Laboratory | Group | Reference range |
|---|---|---|
| Unilabs(Saltro, Medlon, SHO, Atalmedial)2026 | Women 14–19 yrs | 2.20–2.62 mmol/L |
| Men 14–19 yrs | 2.30–2.77 mmol/L | |
| From 19 yrs | 2.15–2.55 mmol/L | |
| Call-back limit, low | < 1.80 mmol/LDecision limit | |
| Call-back limit, high | > 3.00 mmol/LDecision limit | |
| Star-shl2026 | From 18 yrs | 2.20–2.65 mmol/L |
| Certe2026 | All 13–19 yrs | 2.23–2.57 mmol/L |
| From 19 yrs | 2.18–2.55 mmol/L | |
| Clinical Diagnostics2026 | From 18 yrs | 2.20–2.65 mmol/L |
Each band as the lab publishes it, retrieved in 2026, unless marked otherwise.
Calcium high or low: what it means
A low calcium usually means binding or regulation, and almost never diet. In order of how often it occurs: a low albumin, in which the total falls while the free part is normal, and then corrected calcium or free calcium is the more honest measure; a vitamin D deficiency, in which the gut absorbs too little and PTH takes it from the bones; a kidney disease, in which the kidney no longer activates vitamin D and holds on to phosphate; and a low magnesium, without which the parathyroid glands release no PTH. Rare are parathyroid glands that work too little, usually after a neck operation. Tingling around the mouth and in the fingers, cramps and a cramped hand are the symptoms of a really low free calcium. A high calcium you take seriously. Overactive parathyroid glands are the most common reason in anyone who feels well, and you recognise them by a PTH that is not low beside a high calcium. Dehydration concentrates the blood and lifts the total; a tight tourniquet or a clenched fist does the same during the draw, and both recover with a calm repeat. Medicines such as thiazide diuretics, lithium, too much vitamin D or calcium tablets lift the value. A malignancy, usually with symptoms and a low PTH, is the reason a high calcium in someone who is ill is investigated the same week. Prolonged bed rest lets unloaded bones release calcium. What you do about it: with a low calcium from vitamin D you top up vitamin D, and the calcium follows in weeks; eat calcium from dairy, green vegetables, nuts, legumes and fish, and load your bones. With a low magnesium you top that up first. With a low albumin the calcium itself is not the problem. With a high calcium from dehydration you drink and repeat; from medicines or supplements you stop them; from a parathyroid gland an operation is the way once the calcium is high enough or the bones and kidneys suffer, and until then drinking plenty, exercise and no calcium tablets help. Always read calcium beside albumin, because that says whether the total can be trusted, beside PTH with every deviating value, beside vitamin D and magnesium with a low value, and beside creatinine and the eGFR, which say whether the kidneys are involved. ALP shows whether the bones are remodelling.
What lowers it
Usually binding or regulation, and almost never diet.
| Cause | How often |
|---|---|
| Low albuminHalf the calcium is bound to albumin; if that is low, the total falls while the working part stays normal | Often |
| Vitamin D deficiencyThe gut absorbs too little calcium and PTH takes it from the bones; very common in the Netherlands from October to April | Often |
| Kidney diseaseThe kidney no longer activates vitamin D and holds on to phosphate that binds calcium; creatinine and the eGFR show that | Sometimes |
| Low magnesiumWithout magnesium the parathyroid glands release no PTH; the calcium only comes back once magnesium is topped up | Sometimes |
| Underactive parathyroid glandsUsually after an operation on the thyroid or the neck; the calcium falls while the phosphate rises | Rare |
What raises it
Take seriously, even without symptoms, and PTH says which way it goes.
| Cause | How often |
|---|---|
| Overactive parathyroid glandsThe most common reason in anyone who feels well, often found by chance; recognisable by a PTH that is not low beside a high calcium | Often |
| DehydrationThe blood concentrates and the total calcium rises along; water and a repeat solve it | Often |
| Tourniquet or a clenched fistCongestion during the draw squeezes fluid out of the blood and lifts the calcium; a calm repeat gives your true value | Sometimes |
| MedicinesThiazide diuretics, lithium, too much vitamin D and calcium tablets; stopping lets the value fall | Sometimes |
| MalignancyA tumour that breaks down bone or makes a substance resembling PTH; usually with symptoms and a low PTH, and investigated the same week | Sometimes |
| Prolonged bed restBones that are not loaded release calcium; moving and loading reverses it | Rare |
How does a calcium blood test work?
- Referral
- Not needed. Calcium is in most blood tests and you can have it measured yourself, preferably with albumin alongside, and with a deviating value with PTH and vitamin D.
- Fasting
- Not strictly needed, though preferably measured fasting so a calcium-rich meal or a tablet just before does not lift the value.
- When
- Well hydrated and at a calm moment. Skip calcium tablets and vitamin D on the day of the draw if you want to know your usual level.
- The draw
- One tube of blood from a vein in your arm, with a loose tourniquet and a relaxed hand, because congestion and pumping lift the calcium. Albumin, PTH, vitamin D and creatinine come from the same draw.
- Which test
- Calcium is in the comprehensive test (€229) and in .
- Where to draw
- You can draw at 350+ locations near you, no referral needed. See the locations
Frequently asked questions
The mineral of your bones, where more than ninety-nine percent of it sits. The small part in your blood is the working stock your nerves fire with, your muscles contract with, your heart keeps its rhythm with and your blood clots with. Your body holds that part within a narrow band with PTH and vitamin D, and uses your bones as reserve. That is why the blood value says little about how much calcium you eat.
Related biomarkers
Read on
Sources
- 1.Unilabs, test catalogue (Dutch): calcium. 2026. bepalingenklapper.nl
- 2.Star-shl, test catalogue (Dutch): calcium. 2026. star-shl.nl
- 3.Certe, test catalogue (Dutch): total calcium. 2026. bepalingenwijzer.certe.nl
- 4.Clinical Diagnostics, lab guide (Dutch): calcium. 2026. clinicaldiagnostics.nl
- 5.LESA Laboratory diagnostics (Dutch primary-care laboratory agreement). 2026. richtlijnen.nhg.org
Educational information only, not medical advice. Consult a healthcare professional for clinical decisions.
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