Background: Whether anti-severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) antibody levels post-third coronavirus disease (COVID-19) vaccination correlate with worse outcomes due to breakthrough infection is unclear. We evaluated the association between anti-SARS-CoV-2 antibody levels and symptomatic breakthrough infection or hospitalization during the Omicron surge in kidney transplant recipients. Methods: In total, 287 kidney transplant recipients expected to receive a third vaccination were enrolled between November 2021 and February 2022. The Abbott SARS-CoV-2 IgG II Quant test (Abbott, Chicago, IL, USA) was performed within three weeks before and four weeks after the third vaccination. The incidence of symptomatic breakthrough infection and hospitalization from two weeks to four months post-third vaccination was recorded. Results: After the third vaccination, the seropositive rate and median antibody titer of the 287 patients increased from 57.1% to 82.2% and from 71.7 (interquartile range [IQR] 7.2– 402.8) to 1,612.1 (IQR 153.9–5,489.1) AU/mL, respectively. Sixty-four (22.3%) patients had symptomatic breakthrough infections, of whom 12 required hospitalization. Lower anti-receptor-binding domain (RBD) IgG levels ( < 400 AU/mL) post-third vaccination were a risk factor for symptomatic breakthrough infection (hazard ratio [HR] = 3.46, P < 0.001).Anti-RBD IgG levels < 200 AU/mL were a critical risk factor for hospitalization (HR = 36.4, P = 0.007). Conclusions Low anti-spike IgG levels after third vaccination in kidney transplant recipients were associated with symptomatic breakthrough infection and, particularly, with hospitalization during the Omicron surge. These data can be used to identify patients requiring additional protective measures, such as passive immunization using monoclonal antibodies.

Hematuria is the presence of blood in the urine and is classified as either gross hematuria or microscopic hematuria. There are many causes of hematuria, and the differential diagnosis depends on the presence or absence of comorbidities and whether it is glomerular or non-glomerular. When hematuria in children is symptomatic or persistent, an evaluation of the cause is essential. The causes of hematuria and basic approaches to its diagnosis are discussed in this review.

Distinguishing lupus nephritis (LN) from other glomerulopathies, such as immunoglobulin A nephropathy (IgAN), poses a diagnostic challenge owing to overlapping clinical and histopathologic findings. Lupus anticoagulant-hypoprothrombinemia syndrome (LAHPS) is a rare and potentially fatal disorder characterized by the presence of lupus anticoagulant and acquired factor II deficiency. We report a pediatric case of LN with LAHPS, which was initially diagnosed as IgAN. An 8-year-old girl presented with gross hematuria with nephrotic syndrome. Based on the kidney biopsy results, treatment for IgAN with membranoproliferative pattern was initiated. Two months later, she developed left upper extremity swelling with multiple vein thromboses requiring anticoagulation; treatment led to remission, allowing discontinuation of immunosuppressants within 8 months. Gross hematuria recurred 10 months later and was accompanied by hypocomplementemia; positive antinuclear, anti-double stranded DNA, and triple antiphospholipid antibodies; and factor II deficiency, prompting revision of the diagnosis to LN and LAHPS. Initial delay in LN diagnosis was attributed to the patient’s young age, nonspecific symptoms, and inconclusive laboratory and histopathological findings. Immunosuppressive therapy for IgAN partially improved LN, further complicating the diagnosis. This case emphasized the importance of clinical suspicion; integrating clinical, serological, and histopathological data; and considering LAHPS in differential diagnosis of glomerulonephritis with coagulopathy.

Persistent proteinuria is an important indicator of kidney damage and requires active evaluation and intervention. However, tubular proteinuria of genetic origin typically does not improve with immunosuppression or antiproteinuric treatment. Recently, defects in CUBN were found to cause isolated proteinuria (mainly albuminuria) due to defective tubular albumin reuptake. Unlike most other genetically caused persistent albuminuria, CUBN C-terminal variants have a benign course without progression to chronic kidney disease according to the literature. Here, we present Korean cases with persistent proteinuria associated with C-terminal variants of CUBN. Methods: We identified Korean patients with CUBN variants among those with an identified genetic cause of proteinuria and evaluated their clinical features and clinical course. We also reviewed the literature on CUBN-associated isolated proteinuria published to date and compared it with Korean patients. Results: All patients presented with incidentally found, asymptomatic isolated proteinuria at a median age of 5 years. The proteinuria was in the subnephrotic range and did not significantly change over time, regardless of renin- angiotensin system inhibition. Initial physical examination, laboratory findings, and kidney biopsy results, when available, were unremarkable other than significant proteinuria. All patients maintained kidney function throughout the follow-up duration. All patients had at least one splicing mutation, and most of the variants were located C-terminal side of the gene. Conclusion: We report Korean experience of CUBN-related benign proteinuria, that aligns with previous reports, indicating that this condition should be considered in cases with incidentally found asymptomatic isolated proteinuria, especially in young children.

Hematuria is a relatively common condition among school-aged children. Because international guidelines for asymptomatic hematuria in children are unavailable, developing practical guidelines for the diagnosis and management of asymptomatic hematuria based on scientific evidence while considering real-world practice settings, values, and patient and physician preferences is essential. The Korean Society of Pediatric Nephrology developed clinical guidelines to address key questions regarding the diagnosis and management of asymptomatic hematuria in children.

Persistent proteinuria is an important indicator of kidney damage and requires active evaluation and intervention. However, tubular proteinuria of genetic origin typically does not improve with immunosuppression or antiproteinuric treatment. Recently, defects in CUBN were found to cause isolated proteinuria (mainly albuminuria) due to defective tubular albumin reuptake. Unlike most other genetically caused persistent albuminuria, CUBN C-terminal variants have a benign course without progression to chronic kidney disease according to the literature. Here, we present Korean cases with persistent proteinuria associated with C-terminal variants of CUBN. Methods: We identified Korean patients with CUBN variants among those with an identified genetic cause of proteinuria and evaluated their clinical features and clinical course. We also reviewed the literature on CUBN-associated isolated proteinuria published to date and compared it with Korean patients. Results: All patients presented with incidentally found, asymptomatic isolated proteinuria at a median age of 5 years. The proteinuria was in the subnephrotic range and did not significantly change over time, regardless of renin- angiotensin system inhibition. Initial physical examination, laboratory findings, and kidney biopsy results, when available, were unremarkable other than significant proteinuria. All patients maintained kidney function throughout the follow-up duration. All patients had at least one splicing mutation, and most of the variants were located C-terminal side of the gene. Conclusion: We report Korean experience of CUBN-related benign proteinuria, that aligns with previous reports, indicating that this condition should be considered in cases with incidentally found asymptomatic isolated proteinuria, especially in young children.

Hematuria is a relatively common condition among school-aged children. Because international guidelines for asymptomatic hematuria in children are unavailable, developing practical guidelines for the diagnosis and management of asymptomatic hematuria based on scientific evidence while considering real-world practice settings, values, and patient and physician preferences is essential. The Korean Society of Pediatric Nephrology developed clinical guidelines to address key questions regarding the diagnosis and management of asymptomatic hematuria in children.

Persistent proteinuria is an important indicator of kidney damage and requires active evaluation and intervention. However, tubular proteinuria of genetic origin typically does not improve with immunosuppression or antiproteinuric treatment. Recently, defects in CUBN were found to cause isolated proteinuria (mainly albuminuria) due to defective tubular albumin reuptake. Unlike most other genetically caused persistent albuminuria, CUBN C-terminal variants have a benign course without progression to chronic kidney disease according to the literature. Here, we present Korean cases with persistent proteinuria associated with C-terminal variants of CUBN. Methods: We identified Korean patients with CUBN variants among those with an identified genetic cause of proteinuria and evaluated their clinical features and clinical course. We also reviewed the literature on CUBN-associated isolated proteinuria published to date and compared it with Korean patients. Results: All patients presented with incidentally found, asymptomatic isolated proteinuria at a median age of 5 years. The proteinuria was in the subnephrotic range and did not significantly change over time, regardless of renin- angiotensin system inhibition. Initial physical examination, laboratory findings, and kidney biopsy results, when available, were unremarkable other than significant proteinuria. All patients maintained kidney function throughout the follow-up duration. All patients had at least one splicing mutation, and most of the variants were located C-terminal side of the gene. Conclusion: We report Korean experience of CUBN-related benign proteinuria, that aligns with previous reports, indicating that this condition should be considered in cases with incidentally found asymptomatic isolated proteinuria, especially in young children.

Hematuria is a relatively common condition among school-aged children. Because international guidelines for asymptomatic hematuria in children are unavailable, developing practical guidelines for the diagnosis and management of asymptomatic hematuria based on scientific evidence while considering real-world practice settings, values, and patient and physician preferences is essential. The Korean Society of Pediatric Nephrology developed clinical guidelines to address key questions regarding the diagnosis and management of asymptomatic hematuria in children.