Dynamics of d-serine reflected the recovery course of a patient with rapidly progressive glomerulonephritis

We experienced a case of a 36-year-old female with rapidly progressive glomerulonephritis (RPGN) due to anti-neutrophil cytoplasmic antibody (ANCA)-associated nephritis and systemic lupus erythematosus (SLE) nephritis. Chiral amino acid metabolomics revealed a prominent profile of d-serine in this patient. At the fulminant period of RPGN, the level of plasma d-serine, a potential biomarker in CKD that reflects actual glomerular filtration ratio (GFR), was extremely high. On the other hand, urinary fractional excretion (FE) of d-serine, which was usually much higher than that of l-isoform, was 0% in this patient. These abnormal d-serine profiles normalized in response to the intensive treatment. Normalizations of blood d-serine levels were in parallel with those of blood creatinine levels and potentially reflect the recovery of GFR. FE of d-serine increased transiently before the normalization of d-serine profile, suggesting that kidney promotes urinary excretion of d-serine for the normalization of plasma d-serine level. These unexplored clinical features of d-serine well reflected the clinical course of this patient. Blood d-serine level can also serve as a biomarker in acute kidney injury (AKI) or RPGN, and, in combination with FE of d-serine, may render the clinical practitioners to judge the efficacy of intensive treatments. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s13730-019-00411-6) contains supplementary material, which is available to authorized users.