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. 2021 Jun 3;2(9):1482-1490.
doi: 10.34067/KID.0000362021. eCollection 2021 Sep 30.

Comparison of Patients with Hospital-Recorded Nephrotic Syndrome and Patients with Nephrotic Proteinuria and Hypoalbuminemia: A Nationwide Study in Denmark

Søren Viborg Vestergaard  1 , Henrik Birn  2   3 , Anette Tarp Hansen  1   4 , Mette Nørgaard  1 , Dorothea Nitsch  5 , Christian Fynbo Christiansen  1
Affiliations

Comparison of Patients with Hospital-Recorded Nephrotic Syndrome and Patients with Nephrotic Proteinuria and Hypoalbuminemia: A Nationwide Study in Denmark

Søren Viborg Vestergaard et al. Kidney360. .

Abstract

Background: Registry-based studies of nephrotic syndrome (NS) may only include a subset of patients with biochemical features of NS. To address this, we compared patients with laboratory-recorded nephrotic proteinuria and hypoalbuminemia to patients with hospital-recorded NS.

Methods: We identified adult patients with first-time hospital-recorded NS (inpatients, outpatients, or emergency-room visitors) in the Danish National Patient Registry and compared them with adults with first-time recorded nephrotic proteinuria and hypoalbuminemia in Danish laboratory databases during 2004-2018, defining the date of admission or laboratory findings as the index date. We characterized these cohorts by demographics, comorbidity, medication use, and laboratory and histopathologic findings.

Results: We identified 1139 patients with hospital-recorded NS and 5268 patients with nephrotic proteinuria and hypoalbuminemia; of these, 760 patients were identified in both cohorts. Within 1 year of the first record of nephrotic proteinuria and hypoalbuminemia, 18% had recorded hospital diagnoses indicating the presence of NS, and 87% had diagnoses reflecting any kind of nephropathy. Among patients identified with nephrotic proteinuria and hypoalbuminemia, their most recent eGFR was substantially lower (median of 35 versus 61 ml/min per 1.73 m2), fewer underwent kidney biopsies around the index date (34% versus 61%), and the prevalence of thromboembolic disease (25% versus 17%) and diabetes (39% versus 18%) was higher when compared with patients with hospital-recorded NS.

Conclusions: Patients with nephrotic proteinuria and hypoalbuminemia are five-fold more common than patients with hospital-recorded NS, and they have a lower eGFR and more comorbidities. Selective and incomplete recording of NS may be an important issue when designing and interpreting studies of risks and prognosis of NS.

Keywords: albuminuria; algorithms; epidemiology; glomerular and tubulointerstitial diseases; hospital records; hypoalbuminemia; nephrotic syndrome; proteinuria.

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Conflict of interest statement

S.V. Vestergaard, H. Birn, A.T. Hansen, M. Nørgaard, and C.F. Christiansen have no personal conflicts of interest to declare regarding this study. The Department of Clinical Epidemiology, The Department of Biomedicine, and the Department of Renal Medicine are involved in studies with funding from various companies as research grants to (and administered by) Aarhus University or Aarhus University Hospital. None of these studies are related to this study. D. Nitsch is on the steering group for two GlaxoSmithKline-funded studies of kidney function in sub-Saharan Africa, unrelated to the work in this paper.

Figures

None
Graphical abstract
Figure 1.
Figure 1.
Among 5268 adults with first-time nephrotic proteinuria and hypoalbuminemia, majority had diagnoses reflecting nephropathy recorded in the Danish National Patient Registry around the index date (day 0), but no more than 18% had a diagnosis specific to nephrotic syndrome after one year. Cumulative proportions of patients with kidney diseases recorded in the Danish National Patient Registry from 1 year before to 1 year after the index date (day 0) among 5268 adults with first-time nephrotic proteinuria and hypoalbuminemia during 2004–2018. *Nephrotic syndrome; **GN (including nephrotic syndrome) or diabetic nephropathy; and ***GN (including nephrotic syndrome), diabetic nephropathy, SLE, sicca (Sjögren) syndrome, glomerular diseases, renal tubulointerstitial diseases, acute kidney failure and CKD, disorder of kidney and ureter (unspecified), amyloidosis, and hypertension with nephropathy.
Figure 2.
Figure 2.
Among 1139 patients with first-time hospital-recorded nephrotic syndrome, the majority had a first recording of nephrotic proteinuria and hypoalbuminemia close to the index date (day 0). Cumulative proportions of patients with any recorded proteinuria test, nephrotic proteinuria, or nephrotic proteinuria and hypoalbuminemia from 1 year before to 1 year after the index date (day 0) among 1139 patients with first-time hospital-recorded nephrotic syndrome.
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