# Improving the diagnostic of absorptive hypercalciuria: a comparative analysis of calcium load tests at 2-hour and 4-hour intervals

## TL;DR

This study shows that a 4-hour calcium load test is more effective than a 2-hour test for diagnosing absorptive hypercalciuria.

## Contribution

The study demonstrates that extending the calcium load test to 4 hours significantly improves the detection of absorptive hypercalciuria.

## Key findings

- The 4-hour CLT diagnosed 25.6% more cases of absorptive hypercalciuria compared to the 2-hour CLT.
- The urinary calcium/creatinine ratio increased significantly after 4 hours of calcium ingestion.
- Patients diagnosed at 4 hours showed similar clinical and biological profiles to those diagnosed at 2 hours.

## Abstract

The calcium load test (CLT) was developed by Pak et al. in 1974 to better discriminate hypercalciuria. Absorptive hypercalciuria (AH) is defined by an increase of the difference between urinary calcium/creatinine ratio (ΔUCa/Cr) of more than 0.5 mmol/mmol with a 4-hour CLT. In clinical practice and more recent studies, CLT is a 2-hour test. We hypothesized that the 4 h timepoint is more efficient in AH diagnosis.

We report a single-centre retrospective study including all patients who underwent CLT because of hypercalciuria or hyperparathyroidism. After a 3-day low-calcium diet and a 12-hour fast, 24-hour urines were collected. Blood and urinary samples were done at arrival and after 2 h and 4 h of oral ingestion of 1 g of calcium. AH was diagnosed by ΔUCa/Cr between baseline and 2 h or 4 h of more than 0.05 mmol/mmol.

We included 328 patients. Baseline UCa/Cr ratio was 0.3 ± 0.2 mmol/mmol and increased significantly after 2 h and 4 h (0.6 ± 0.3 and 0.8 ± 0.4 mmol/mmol, P < 0.001). ΔUCa/Cr was significantly different between baseline and 2 h or 4 h (0.2 ± 0.2 versus 0.5 ± 0.4, P < 0.001). AH was diagnosed in 35 (10.7%) patients after 2 h, 84 (25.6%) more were diagnosed at 4 h (P < 0.001).

The 4 h CLT improves the diagnosis of AH with more than 50% of AH diagnosed within 4 h of calcium ingestion. It seems that there are cases of AH of later diagnosis with a similar clinical and biological profile depending on enteral absorption.

Graphical Abstract