Challenges in diagnostic testing of nephritic factors

C3 concentrations can be normal in patients with C3 glomerulopathy secondary to C3 nephritic factor

C3 glomerulopathy (C3G) is a rare kidney disease caused by the glomerular deposition of C3 fragments secondary to alternative pathway complement dysregulation. C3 nephritic factors (C3Nef) are the most common acquired cause, and their detection has treatment and prognostic implications. Although C3 concentration can be normal in the presence of C3Nef, many laboratories will only perform C3Nef testing when C3 is low. We performed a retrospective study of all positive C3Nef results from the authors' laboratory since 2015 and found that two of the four patients with positive C3Nef and biopsy-confirmed C3G had normal C3 concentrations. This may be in part due to limitations in commercial C3 testing methods which use anti-C3c antisera directed against both C3 breakdown products and native C3. A normal C3 concentration should not preclude C3Nef testing in the appropriate clinical context.

Expert Discussion on Challenges in C3G Diagnosis: A Podcast Article on Best Practices in Kidney Biopsies

Complement 3 glomerulopathy (C3G) is an ultra-rare, progressive kidney disease resulting from dysregulation of the alternative complement pathway. Clinical presentation of C3G is heterogeneous and definitive diagnosis relies on kidney biopsy and immunofluorescence staining. The term C3G encompasses two subgroups, dense deposit disease and C3 glomerulonephritis, distinguished via electron microscopy. In this podcast article, the authors discuss the challenges associated with C3G diagnosis and the central role of kidney biopsy. Using an illustrative case study, key histological observations are described, and best practices are discussed from the perspectives of a nephrologist and a nephropathologist. Podcast Audio (MP4 141866 KB).

C3 Glomerulonephritis Presenting With Nephritic and Nephrotic Syndromes: Spontaneous Remission After Six Months on Dialysis

C3 glomerulopathy is a rare and complex renal disease driven by complement dysregulation, with variable presentation and pathophysiology. We report the case of a middle-aged male patient presenting with nephritic and nephrotic syndromes and low serum C3, whose biopsy established the diagnosis of C3 glomerulonephritis. He was found to be homozygous for the complement factor H-related protein (CFHR)3-CFHR1 deletion, which has been associated with the development of anti-factor H autoantibodies. However, the lack of consistent and accessible nephritic factor assays prevented full clarification of the mechanisms involved in the disease. Interestingly, despite not receiving treatment due to suspicion of malignancy and perceived poor renal prognosis, there was spontaneous recovery after six months on hemodialysis. This case reflects the enduring challenges in establishing the diagnosis and prognosis of C3 glomerulonephritis.