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Urine Calcium-to-Creatinine Ratio

Calcium in one urine sample compared with creatinine, which adjusts for how dilute the urine is. It is used for stone and bone work-ups in adults and children.

AI-verified against cited sources. Awaiting expert reviewAlso called Ca/Cr, UCa/CrLOINC 9321-1

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What it is

This test measures calcium and creatinine in the same urine sample and divides one by the other. Creatinine is a waste product your muscles release at a fairly steady rate, so the ratio adjusts for how watery or concentrated the urine is. That lets a lab estimate how much calcium you are losing without a 24-hour collection. Normal values are higher in babies and fall through childhood to adult levels.

Why it matters

Mayo Clinic Laboratories lists this ratio for judging kidney stone risk and for looking into bone diseases such as osteoporosis and osteomalacia. It is also a practical option in children, when a 24-hour collection is hard to get. In adults who form stones, a 24-hour collection is still the main test, so a ratio is often a first look. The ratio comes from one sample, so it can swing with meals and fluids. Unexpected results are often repeated or followed by a 24-hour collection.

If it’s low

A lower ratio means less calcium was leaving in the urine, compared with creatinine. It often fits a low-calcium diet, and it is often harmless. A few hormone and kidney conditions cause it, so your clinician will read it alongside your blood calcium, vitamin D and PTH.

Common causes

  • Eating little calcium
  • Conditions that make it hard to absorb nutrients from food, or malnutrition
  • Severe vitamin D deficiency
  • Thiazide diuretics, a type of water pill that helps kidneys hold on to calcium
  • Underactive parathyroid glands (hypoparathyroidism)
  • Kidney disease
  • Familial hypocalciuric hypercalcemia, an inherited condition that raises blood calcium but usually keeps urine calcium low

What can help

  • Ask whether your calcium intake and vitamin D level are in a good range
  • Ask whether blood calcium, vitamin D or PTH tests would help explain the result

If it’s high

A higher ratio means more calcium was leaving in the urine, compared with creatinine, than your lab's usual range for your age. It is linked to calcium kidney stones and can reflect diet, supplements or medicines. It can also be a sign that the parathyroid glands, vitamin D level or bones need a closer look, so your clinician will read it together with your blood calcium.

Common causes

  • A diet high in salt (sodium) or animal protein
  • Idiopathic hypercalciuria, meaning high urine calcium with no other cause found, which is the most common finding in people who keep forming calcium stones
  • Calcium supplements or calcium-based antacids
  • Too much vitamin D
  • Loop diuretics, a type of water pill
  • Overactive parathyroid glands (hyperparathyroidism)
  • Sarcoidosis, or some bone conditions
  • Some kidney conditions

What can help

  • Ask your clinician whether eating less salt and less animal protein could help, since both raise urine calcium
  • Ask before cutting back on calcium-rich foods. Eating less calcium can raise the oxalate your body absorbs, which can make stones more likely
  • Review your calcium and vitamin D supplements, antacids and other medicines with your clinician
  • Ask whether a 24-hour urine collection or blood calcium and PTH tests would help

Usual ranges

What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.

The usual range depends on age. Choose an age to see the one that applies.

Children and teens 7 ranges

See Urine Ca/Cr ratio by age and sex, with the U.S. survey numbers where they exist.

What can affect your result

  • Age: babies and young children normally have higher ratios (Mayo's upper limit is 0.81 mg/mg at 1-11 months and 0.27 mg/mg in adults)
  • Diet, especially salt, protein and calcium
  • Meals and fluids around the time of the sample
  • Muscle mass, age and sex, which change creatinine output
  • Calcium and vitamin D supplements, antacids and diuretics
  • Units: labs print mg/mg or mg/g (1 mg/mg = 1,000 mg/g), and some print mmol/mmol
  • What you ate and drank around the sample matters, especially salt (sodium), protein and calcium, so a single sample can swing from one day to the next.
  • Creatinine output varies with muscle mass, age and sex, so the ratio is an estimate of calcium loss rather than an exact measure.
  • Calcium or vitamin D supplements, calcium-based antacids and diuretics can change the result.

A random urine sample. Your clinician or lab may give timing instructions, such as a particular time of day, so follow what you are told. A snapshot of the sample collected. Diet, fluids and medicines can change it from one sample to the next.

When to talk to a clinician

A urine calcium result on its own is not an emergency. Talk with the clinician who ordered it about any result outside your lab's range. See a clinician promptly for sharp pain in your side, back, lower belly or groin, blood in your urine, pain when you urinate, or fever and chills, since these can go with a kidney stone or an infection. Get urgent care if you can't urinate at all or only pass a little.

Questions you could ask

  • Should we repeat this on another day to confirm it?
  • Is the age-based range used on my report the right one for me or my child?
  • Could my salt or protein intake explain this result?
  • Would a 24-hour urine collection or blood calcium and PTH tests help?
  • Could any of my supplements or medicines be raising my urine calcium?
  • Is my calcium and vitamin D intake enough?

Questions people ask

Why is my child's ratio higher than an adult's?

Babies and young children normally release more calcium for each unit of creatinine, so labs use age-specific ranges. At Mayo Clinic Laboratories the upper limit is 0.81 mg/mg at 1-11 months and falls to 0.27 mg/mg in adults.

How do I convert between mg/mg, mg/g and mmol/mmol?

Multiply mg/mg by 1,000 to get mg/g, so 0.2 mg/mg is 200 mg/g. To turn mmol/mmol into mg/mg, multiply by about 0.354.

Is the ratio as good as a 24-hour urine collection?

It is much easier to collect, but it is a single snapshot and can move with meals and fluids. For kidney stone work-ups in adults, a 24-hour collection is usually the main test, and the ratio is often a first look.

Show the science and sources

Units

  • 1 mg/mg = 1 mg/mg
  • 1 mg/mg = 1000 mg/g

Open the Urine Ca/Cr ratio unit converter

For clinicians and researchers

Mayo's CACR3 calculates the ratio (CCTR, LOINC 9321-1) from photometric calcium (CALC5, 17862-4) and colorimetric creatinine (CRETR, 2161-8) in a random urine, and reports mg calcium per mg creatinine with age bands from 1 month to 83 years: 0.03-0.81 (1-<12 months), 0.03-0.56 (12-<24 months), 0.02-0.50 (24 months-<3 years), 0.02-0.41 (3-<5), 0.01-0.30 (5-<7), 0.01-0.25 (7-<10), 0.01-0.24 (10-<18) and 0.05-0.27 (18-83 years); values are not established under 1 month or over 83 years. ARUP reports mg/g (component LOINC 13717-4, a 24-hour code) with male/female intervals for 18 and older of 20-240 and 20-300 mg/g and age bands for children (for example 30-810 mg/g at 0-11 months and 10-300 mg/g at 5-6 years). ARUP's upper limits are higher than Mayo's for ages 7-17 (264-457 mg/g, about 0.26-0.46 mg/mg, versus 0.24-0.25). Molar ratios (mmol/mmol, LOINC 24518-3) convert to mg/mg by multiplying by about 0.354 (atomic weight of calcium 40.08 divided by creatinine 113.12), but this catalog does not encode the molar unit because the validator treats mass/mass and mol/mol as the same dimension. Creatinine excretion tracks muscle mass, so the ratio is a proxy for the 24-hour excretion, which AJKD 2023 calls the cornerstone of stone evaluation. Interpretation of hypercalciuria thresholds in stone care (more than 4 mg/kg/24 h, or more than 250-300 mg/24 h) applies to 24-hour collections, not to spot ratios.

LOINC 9321-1 (primary), 13717-4, 24518-3, 50839-0. Specimen: urine.

Sources

  1. Calcium/Creatinine Ratio, Random, Urine (Mayo test CACR3), Mayo Clinic Laboratories
  2. Calcium, Urine (ARUP test 0020472), ARUP Laboratories
  3. Calcium in Urine Test (MedlinePlus Medical Test), MedlinePlus, U.S. National Library of Medicine
  4. Calcium - urine (MedlinePlus Medical Encyclopedia), MedlinePlus, U.S. National Library of Medicine (2025)
  5. Nutritional Management of Kidney Stones (Nephrolithiasis), Clinical Nutrition Research (2015)
  6. Kidney Stone Pathophysiology, Evaluation and Management: Core Curriculum 2023, American Journal of Kidney Diseases (2023)
  7. European expert consensus on practical management of specific aspects of parathyroid disorders in adults and in pregnancy: recommendations of the ESE Educational Program of Parathyroid Disorders (PARAT 2021), European Journal of Endocrinology (European Society of Endocrinology) (2022)

AI-verified against cited sources. Awaiting expert review. Last reviewed 2026-10-03. How we build and check these pages.

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