A Low Calcium with a Low Albumin
Roughly half the calcium in your blood is not free. It travels stuck to albumin, and the standard test measures both halves together. So when albumin falls, the total falls with it while the free calcium that your nerves and muscles actually use has not changed at all. This is usually a reporting artifact rather than a deficiency, and the corrected calcium on the same report tells you which.
The pattern on your report
- Calcium Low · mild Key
- Albumin Low · moderate Key
- Phosphate Normal Key
- Magnesium Normal Supporting
Printed as: Albumin in g/Lor g/dLCalcium in mmol/Lor mg/dL— Total, adjusted and ionized calcium are three different measurements. Check which one your report is giving before comparing it with anything.Magnesium in mmol/Lor mg/dLPhosphate in mmol/Lor mg/dL
Why the numbers look like this
Only the free, or ionized, fraction of calcium does anything. Bound calcium is inert cargo. Because measuring the free fraction directly needs careful sample handling, most laboratories measure the total and adjust it for albumin instead, producing what the report calls an adjusted or corrected calcium.
That adjustment is an estimate, and it is least reliable exactly where it is needed most: in critical illness, in advanced kidney disease, and when albumin is very low. In those situations an ionized calcium measured directly is the test that settles it.
Which means the practical question here is not really about calcium. It is about why the albumin is low, and that question has an answer of its own.
Not being flagged is not the same as normal
Lower limits for total calcium sit near 2.20 mmol/L, about 8.5 mg/dL, and for albumin near 35 g/L. The two move together closely enough that a report showing both flagged low is the expected consequence of one problem, not evidence of two. What matters is whether the corrected calcium is also low: if it is not, the calcium is fine.
What else on the report can hide this
Read the albumin as the finding and the calcium as its shadow. A low albumin has a short and useful differential of its own, and a urine protein test is the cheapest thing that changes the answer, since heavy protein loss through the kidney is one of the few causes that is both common and specific.
Magnesium deserves the same attention it gets with potassium. A low magnesium impairs both the release of PTH and its effect on tissue, so replacing calcium fails until the magnesium is dealt with first. If the corrected calcium really is low, then vitamin D, PTH and kidney function are the next three, because between them they cover nearly all genuine hypocalcemia.
What usually causes it
Listed from most to least common — not from most to least serious.
- Very common
A low albumin with normal free calcium
The commonest explanation by a wide margin. The corrected calcium is normal and nothing needs treating. What needs explaining is the albumin.
- Very common
Acute illness or inflammation
Albumin falls quickly in any inflammatory state, which is why an inpatient panel so often shows this pair. It recovers as the illness does.
- Common
Protein loss through the kidney
Nephrotic-range proteinuria drops albumin substantially. A urine protein or ACR test finds it, and it is the cause not to miss.
- Common
Liver disease
Reduced synthesis. Usually with other liver abnormalities, a raised INR, or a low platelet count.
- Common
Malnutrition or malabsorption
Celiac disease, inflammatory bowel disease, or simply poor intake in frailty. Often with a low B12 or ferritin alongside.
- Common
Vitamin D deficiency
Genuinely lowers free calcium as well as total. Common where sunlight is limited or skin is covered, and easily corrected once measured.
- Uncommon
Low magnesium
Blocks both the release and the action of PTH, so calcium stays low until magnesium is replaced. Not on most panels.
- Uncommon
Advanced kidney disease
The kidney stops activating vitamin D and stops clearing phosphate, so calcium falls with a high phosphate beside it, which is not the pattern on this page.
- Uncommon
Bisphosphonates or denosumab
Both lower calcium, denosumab sharply in anyone whose vitamin D or kidney function is low, which is why vitamin D is checked before the first dose.
- Uncommon
Hypoparathyroidism
Most often after thyroid or parathyroid surgery. Low calcium with a high phosphate and a low PTH, which is a different pattern from this one.
- Rare
Protein-losing enteropathy
Albumin lost through the gut rather than the kidney, with a normal urine protein. Suspected when nothing else explains a persistently low albumin.
What is usually checked next
- The corrected or adjusted calcium on the same report Says immediately whether there is a calcium problem at all. Often already printed on the report.
- Ionized calcium Measures the fraction that matters directly, and is the right test when the albumin is very low or the person is seriously ill, where the adjustment is least reliable.
- Urine protein or albumin-to-creatinine ratio Finds kidney protein loss, which is the specific and treatable cause of a low albumin.
- Vitamin D, PTH and magnesium Covers nearly all genuine hypocalcemia, and magnesium is the one that makes treatment fail when it is missed.
- Liver panel with INR, and celiac serology Addresses the synthesis and absorption causes of a low albumin.
When to seek care sooner
- Emergency A seizure, or muscle spasms of the hands and face
- Emergency An irregular heartbeat or fainting
- Same day Tingling around the mouth or in the fingers with cramping
- Same day A corrected calcium that is also clearly low
- Same day A low calcium in the days after thyroid or neck surgery
- Soon Frothy urine, or swelling of the legs and around the eyes
Questions worth bringing to your appointment
- What is my corrected calcium, and is it also low?
- Should an ionized calcium be done instead, given how low my albumin is?
- Why is my albumin low, and has my urine been checked for protein?
- Have vitamin D and magnesium been measured?
- Is there anything I should watch for while this is being sorted out?