Calcium Dobesilate Interference in Two Urinary Total Protein Detection Methods

BACKGROUND: This study aimed to determine the potential interference of calcium dobesilate in two urinary total protein detection methods. METHODS: Urine samples from patients receiving calcium dobesilate were collected, and drug concentrations were quantified using liquid chromatography-tandem mass spectrometry. Paired-difference testing was used to assess if calcium dobesilate interfered with the total protein concentration measurement. The interference effect of calcium dobesilate on the detection method was evaluated using dose-effect experiments. RESULTS: In total, 22 24-h urine samples and 50 spot urine samples were collected. The calcium dobesilate concentrations ranged from 76 to 738 mg/L (median: 243 [161, 328] mg/L) and 60-2236 mg/L (median: 370 [195, 667] mg/L) in the 24-h and spot urine samples, respectively. Paired-difference testing showed that the total protein results deviated by 0.8%-12.1% and 13.0%-286.4% with the pyrogallol red-molybdate and benzethonium chloride methods, respectively, when the calcium dobesilate concentration was 4500 mg/L. The dose-response experiment with the benzethonium chloride method demonstrated a "J-shaped" effect; negative interference on the total protein concentration occurred at low and medium calcium dobesilate concentrations, but positive interference occurred at high calcium dobesilate concentrations. CONCLUSIONS: Calcium dobesilate did not significantly interfere with the pyrogallol red-molybdate method but did significantly interfere with the benzethonium chloride method. The direction and degree of interference were related to the urinary protein and drug concentrations. Discontinuing calcium dobesilate for 1-2 days before obtaining a urine sample for total protein detection is recommended.