From the Guidelines
The urine calcium:creatinine ratio is a valuable diagnostic tool that indicates the level of calcium excretion in the urine, helping to identify conditions such as hypercalciuria, which can be a concern in patients with Williams syndrome, as noted in the 2020 study published in Pediatrics 1.
Clinical Significance
The urine calcium:creatinine ratio is particularly useful in assessing the risk of nephrocalcinosis and in managing hypercalcemia. According to the study, if hypercalciuria is found, further evaluation including hydration status assessment, serum calcium measurement, dietary calcium intake assessment, and renal ultrasonography should be performed 1.
Interpretation
A normal ratio is typically considered to be less than 0.2, although this can vary slightly depending on the reference source. An elevated ratio suggests hypercalciuria, which may be associated with various conditions including primary hyperparathyroidism, vitamin D excess, and certain medications. The test's simplicity, requiring only a random urine sample, makes it a convenient initial screening tool for both patients and clinicians.
Clinical Application
In clinical practice, the urine calcium:creatinine ratio is most commonly used as an initial screening tool, with abnormal results often prompting further investigation, such as a 24-hour urine collection for more accurate assessment of calcium excretion. It is also important to consider dietary influences on the ratio, as values can be higher after meals, making fasting samples potentially more reliable for consistent results.
Management Implications
For patients with elevated urine calcium:creatinine ratios, management may involve dietary adjustments, increased hydration, and in some cases, referral to a specialist such as a pediatric nephrologist or endocrinologist for further evaluation and treatment, especially in conditions like Williams syndrome where hypercalcemia and hypercalciuria can be significant concerns 1.
From the Research
Urine Calcium:Creatinine Ratio
The urine calcium:creatinine ratio is a diagnostic tool used to evaluate hypercalciuria, a condition characterized by excessive calcium in the urine.
- It is used to diagnose hypercalciuria, which is a risk factor for osteoporosis and nephrolithiasis 2.
- The ratio is calculated by dividing the amount of calcium in the urine by the amount of creatinine, a waste product found in urine.
Diagnostic Accuracy
The diagnostic accuracy of the urine calcium:creatinine ratio has been evaluated in several studies.
- One study found that the spot urine calcium-to-creatinine ratio (SUCCR) underestimated 24-hour urine calcium measurements and did not reliably diagnose hypercalciuria 2.
- Another study found that the calcium-creatinine ratio in a random urine sample was a simple and reliable method to detect hypercalciuria in children 3.
- A study published in 2016 found that thiazide intake decreased 24-hour urinary calcium excretion and calcium/creatinine clearance ratio in patients with primary hyperparathyroidism 4.
Factors Affecting the Ratio
Several factors can affect the urine calcium:creatinine ratio, including:
- Vitamin D deficiency, which can alter the renal excretion of calcium and affect the diagnostic performance of the urine calcium:creatinine ratio 5.
- Thiazide diuretics, which can decrease urinary calcium excretion and affect the diagnosis of primary hyperparathyroidism 6, 4.
- Body mass index and calcitrophic hormone levels, which can improve the diagnostic accuracy of the spot urine calcium-to-creatinine ratio when adjusted for 2.