Anti-nephrin antibody, measured on an automated platform and tracking relapse

Design

assay development and validation study with parallel reference-method testing and cohort analysis

Population

121 children with biopsy-confirmed minimal change disease or primary focal segmental glomerulosclerosis, plus disease and healthy controls

Primary outcome

analytical performance against immunoprecipitation-Western blot, and clinical associations

Effect

concordance 86.8% (kappa 0.714); antibody detected in 41.3% vs 28.1%; positivity in remission linked to relapse within three months

Anti-nephrin autoantibodies have been recognised in minimal change disease and primary focal segmental glomerulosclerosis for several years, but the assays have been laboratory-specific, qualitative and unavailable outside research. This study built an automated chemiluminescence immunoassay using recombinant nephrin ectodomain on magnetic microparticles, and tested it in 121 children with biopsy-confirmed disease alongside disease controls - genetically confirmed podocytopathies, IgA nephropathy, IgA vasculitis with nephritis, lupus nephritis and ANCA-associated glomerulonephritis - and healthy individuals.

Against immunoprecipitation-Western blot the automated assay agreed 86.8% of the time, kappa 0.714, and detected antibody more often (41.3% against 28.1%), the extra cases being low-level positives that antigen inhibition confirmed as real. Clinically, positivity among those with nephrotic-range proteinuria went with more proteinuria, lower albumin and steroid sensitivity. Higher levels predicted shorter relapse-free survival. And positivity measured during complete remission was associated with relapse within three months, with risk increasing by antibody level.

That last finding is what would change a clinic. Relapse in steroid-sensitive nephrotic syndrome is currently detected by the parent testing urine at home, after it has happened. A blood marker that rises before proteinuria returns would allow pre-emptive action - if the test existed locally, and if anyone had shown that acting on it helps. Neither is yet true. This is a single-centre paediatric cohort with no intervention tested on the result.

• Antibody positivity in remission was associated with relapse within the following three months.
• Positivity went with steroid sensitivity, which is the opposite of how a bad prognostic marker usually behaves.
• The automated assay found low-level positives that the research method missed.
• No trial has tested whether acting on a rising antibody level changes outcome.
• Continue home urine dipstick monitoring; nothing here replaces it.

Why it matters

Relapse in nephrotic syndrome is currently detected after it happens, and this is the first marker plausibly able to precede it.

Don't overread it

A single-centre paediatric cohort with the assay developed and evaluated in the same patients - not yet a validated clinical test.

The statistics, in plain English

A kappa of 0.714 is substantial agreement rather than equivalence, and the automated assay detecting more positives could mean either greater sensitivity or more false positives - the antigen inhibition experiments argue for the former without settling it. The relapse association comes from the same cohort the assay was developed in, which is where performance always looks best; an independent validation cohort is the missing piece.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.