Purpose: To determine the possibility of plasma citrate as a biomarker in patients with glaucoma.
Methods: Twenty-one consecutive Caucasian patients with glaucoma and 21 sex- and age-matched controls were investigated. Plasma citrate, plasma creatinine, urine citrate, and urine creatinine were analyzed by ion chromatography. Mean (±standard deviation) concentrations and the calculated fractional citrate excretions were compared using the Mann-Whitney test. Sensitivity and specificity to detect glaucoma using plasma citrate levels were calculated.
Results: The mean plasma citrate (104.8±23.2 vs. 128.2±31.1 μmol/L; P=0.01) concentrations were significantly lower among the patients with glaucoma, whereas the mean urine citrate concentrations (1.7±0.9 vs. 2.8±1.9 μmol/L; P=0.07) were slightly lower. Mean plasma and mean urine creatinine concentrations showed no significant differences (plasma creatinine: 63.0±16.7 vs. 63.4±15.5 μmol/L; P=0.72; urine creatinine: 9.6±5.1 vs. 11.5±8.4 μmol/L; P=0.67). The calculated fractional citrate excretions were also not different with 12.1% versus 13.6% (P=0.37). Setting the cut-off limit at 110 μmol/L, the plasma citrate level evaluation would have a sensitivity of 66.7% and a specificity of 71.4% to detect glaucoma.
Conclusion: In this masked study, plasma citrate levels were significantly decreased in Caucasian patients with glaucoma giving the possibility to use them eventually as a biomarker. The kidney function was normal in both groups, leaving the etiology of this hypocitraemia yet unexplained.