Long-term prognosis of clinically early IgA nephropathy is not always favorable
© Lee et al.; licensee BioMed Central Ltd. 2014
Received: 7 January 2014
Accepted: 13 June 2014
Published: 19 June 2014
The long-term prognosis of clinically early IgA nephropathy (IgAN) patients remains to be clarified. We investigated the long-term outcomes of IgAN patients with an apparently benign presentation and evaluated prognostic factors for renal survival.
We included patients with biopsy-proven IgAN who had estimated glomerular filtration rates (eGFR) ≥60 mL/min/1.73 m2, normal blood pressure, and proteinuria <0.5 g/day at the time of biopsy. The primary outcome was progression to end-stage renal disease (ESRD). The secondary outcome was a 50% increase in serum creatinine level or an increase in proteinuria to >1 g/day.
The analysis included 153 patients who met the inclusion criteria. At diagnosis, their median systolic blood pressure was 120 (110–130) mmHg, eGFR was 85.9 (74.9–100.1) mL/min/1.73 m2, and proteinuria was 0.25 (0.13–0.38) g/day. Of these, 4 patients died and 6 reached ESRD. The 30-year renal survival rate was 85.5%. Three patients had increased serum creatinine levels and 11 developed proteinuria. Remission was observed in 35 (22.9%) patients. A moderate or severe degree of interstitial fibrosis (adjusted odd ratio [OR] 5.93, 95% confidence interval [CI] 1.44–24.45, P = 0.014) and hypoalbuminemia (adjusted OR 6.18, 95% CI 1.20–31.79, P = 0.029) were independent predictors of the secondary outcome.
This study showed that the prognosis of early IgAN was not always favorable, even resulting in progression to ESRD in some cases. Hypoalbuminemia and interstitial fibrosis should also be considered important prognostic factors in clinically early IgAN patients.
KeywordsIgA nephropathy Interstitial fibrosis Progression of renal failure
IgA nephropathy (IgAN) is a common glomerular disease and an important cause of kidney failure. This disease accounts for more than half of all forms of primary glomerulonephritis in Korea . Although dominant mesangial IgA deposits represent the diagnostic hallmark of IgAN, its clinical features are highly variable, ranging from simple hematuria with or without proteinuria to a rapidly progressive loss of renal function. Therefore, the renal survival and risk factors of long-term IgAN patients have been studied extensively over the last 30 years . Previous studies indicate that the likelihood of dialysis or death can be estimated using three clinical risk factors: urinary protein excretion of more than 1 g/day, high blood pressure exceeding 140/90 mmHg, and a decreased estimated glomerular filtration rate (eGFR) of less than 60 mL/min/1.73 m2 . Among patients with all three risk factors, about 70–80% reached end-stage renal disease (ESRD) and 45% died within 30 years [4, 5]. These clinical prognostic factors also independently predict a poor clinical course. However, information on the long-term outcomes of IgAN patients with a minor presentation is scarce.
Only a few studies have focused on long-term patient and renal outcomes in IgAN patients who had a renal biopsy performed for microscopic hematuria, normal renal function, and minimal proteinuria. Moreover, the results of previous studies are controversial. A recently published European cohort study found that IgAN patients who presented with minor urinary abnormalities and normal renal function did not progress to ESRD, and that more than one-third of patients achieved clinical remission . Research performed in Hong Kong, however, found that 33% of patients with minimal proteinuria and preserved renal function developed more than 1 g/day of proteinuria [7, 8]. In a cohort of Chinese IgAN patients with isolated microscopic hematuria who were followed for up to 12 years, a decrease in renal function was observed in 24% . These studies suggest that IgAN patients require long-term follow-up due to the potential for progressive disease.
Our previously, reported findings on the mortality of IgAN patients, which were obtained from our long-term follow-up data , did not significantly differ from European data . The present study focused on long-term outcomes and prognostic factors for renal survival in clinically early IgAN patients. We hypothesized that even patients presenting with benign manifestations would progress during long-term follow-up.
Ethical approval was obtained from the Institutional Review Board of Seoul National University Hospital (H–1010–055–336), and this study was conducted in accordance with the principles of the Declaration of Helsinki. As the study was retrospective in design and did not involve any interventions, the Institutional Review Board waived informed consent for this study.
Clinical information was collected from a review of computerized medical records. Demographic factors, including age, sex, body mass index, and blood pressure at the time of renal biopsy, were obtained. Blood and urine chemistry parameters were extensively reviewed from the time of renal biopsy to the time of last follow-up. Until 2010, serum creatinine levels were measured by Jaffe kinetic alkaline picrate method using a Hitachi 7600 analyzer (Toshiba, 200FR, Tokyo, Japan). Serum creatinine levels were re-calibrated to an isotope-dilution mass spectrometry assay (Roche diagnostic). The correction equation is as follows: recalibrated serum creatinine = 1.0734 x measured serum creatinine(-0.2418). The eGFR was calculated using the Modification of Diet in Renal Disease equation [11, 12]. Proteinuria was assessed using either a random urine protein to creatinine ratio (normal range, <0.2 g/g creatinine) or 24-h urinary protein measurement. Information on treatments prescribed during the follow-up period was collected, including exposure to immunosuppressive agents and to renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme inhibitors or angiotensin receptor blockers.
All native renal biopsies were processed according to light microscopy, immunofluorescence, and electron microscopy standard techniques. Histopathological changes were evaluated by, two pathologists who reviewed the renal biopsy slides. All IgAN biopsies were staged according to the WHO grading system . The proportions of global sclerosis, segmental sclerosis, and crescent formation in the glomerular area were calculated using results obtained on light microscopy. Mesangial proliferation was also graded as none or minimal, mild, moderate, and severe. In the tubulointerstitial area, the degrees of tubular atrophy (TA), interstitial fibrosis (IF), and interstitial inflammation were graded semi-quantitatively as follows: none or minimal, mild, moderate, and severe.
The primary outcome was ESRD progression or patient death. The start of the follow-up period was taken as the date of renal biopsy. ESRD was defined as progression to eGFR <15 mL/min/1.73 m2, initiation of permanent dialysis, or kidney transplantation. Data on mortality were obtained from the Korean National Statistical Office, and those on ESRD were collected from the Korean ESRD registry [14, 15]. We combined all these data according to the unique identification number issued to all Koreans. The secondary outcome was renal progression, defined as a 50% serum creatinine increase or the development of proteinuria greater than 1 g/day. We also evaluated patient clinical remission, defined as the disappearance of microscopic hematuria confirmed on more than 3 occasions, proteinuria persistently lower than 0.2 g/day, and normal renal function.
The data are presented as frequencies and percentages for categorical variables. Continuous variables are shown as medians and interquartile ranges (IQR). Comparisons between the outcome group and other groups were performed using the χ2 test for dichotomous variables and the Mann–Whitney test for asymmetric continuous variables. Cumulative renal survival was determined by the Kaplan-Meier method. Non-renal deaths were excluded from the renal survival rate analysis. The renal survival time for each patient was computed from the time of renal biopsy to the last follow-up. Associations between baseline variables and outcomes were tested using logistic regression. Potential confounding variables identified a priori included hypoalbuminemia (serum albumin level, <3.5 g/dL), RAS blockade, and pathological changes such as segmental sclerosis, interstitial fibrosis, and tubular atrophy. Variables that showed a significant association (p <0.10) in the univariate analysis or were of considerable theoretical relevance were entered into the multivariate stepwise logistic regression models. Analyses were performed using the SPSS software package (version 20.0, Chicago, IL, USA). All tests were two-tailed, with P-values <0.05 considered statistically significant.
Baseline clinical characteristics of early IgAN patients
Body mass index (kg/m2)
Systolic blood pressure (mmHg)
Serum creatinine (mg/dL)
eGFR (mL/min/1.73 m2)
Serum cholesterol (mg/dL)
Serum albumin (g/dL)
Plasma hemoglobin (g/dL)
Serum IgA (mg/dL)
Follow up duration (months)
RAS blockade (N,%)
Global sclerosis (%)
Segmental sclerosis (%)
Crescent formation (yes,%)
Mesangial proliferation (yes,%)
Tubular atrophy (yes,%)
Interstitial fibrosis (yes,%)
Interstitial inflammation (yes,%)
In the histopathological review, more than half of the patients showed minimal or mild pathological change while 47 (30.7%) patients had advanced pathological change, with WHO grade higher than III. Glomerular crescent formation was found in 9.2% of the patients. Moreover, more than 12% of patients had a moderate to severe degree of mesangial proliferation, TA or IF.
Clinical manifestation of patients who reached to end–stage renal disease
Body mass index (kg/m2)
Blood pressure (mmHg)
Blood urea nitrogen (mg/dL) [10-26]
Serum creatinine (mg/dL) [0.70–1.40]
Creatinine clearance (mL/min)
eGFR (mL/min/1.73 m2)
Serum albumin (g/dL) [3.3–5.2]
Global sclerosis (N/Glom No)
Segmental sclerosis (N/Glom No)
Crescent formation (N/Glom No)
Time to ESRD (months)
Comparison between patients with secondary renal outcome and those without
Renal outcome (-)
Renal outcome (+)
Age at the time of biopsy (years)
Sex (male, %)
Body mass index (kg/m2)
Systolic blood pressure (mmHg)
Serum creatinine (mg/dL)
eGFR (ml/min/1.73 m2)
Global sclerosis ≥ 10%
Segmental sclerosis ≥ 10%
RAS blockade (N, %)
Predictors of outcome
Univariate and multivariate logistic regression analysis for development of outcome
OR (95% CI)
Use of RAS blockade
During follow-up, 36 (31.0%) patients showed loss of proteinuria or microscopic hematuria along with stable blood pressure and renal function, in other words, clinical remission. Patients who achieved clinical remission had low systolic blood pressures (median [IQR], 114 [110–124] mmHg vs 120 [110–120] mmHg), less TA (11.4% vs 12.5%) and less IF (8.6% vs 11.3%). However, these differences were all statistically non-significant. Only the amount of proteinuria (0.28 [0.13–0.41] vs 0.21 [0.09–0.33], P = 0.021) and prescription of RAS blockade (34.3% vs 56.3%, P = 0.042) differed significantly according to clinical remission. Our regression analysis did not find any predictors of clinical remission (data not shown).
The clinical course of IgAN is highly variable. However, it is essential to determine whether a patient is at high risk for renal insufficiency in order to establish an individualized management plan. Forecasting the prognosis of benign IgAN on the basis of the currently known prognostic factors or modeling systems is challenging. Experience gathered over a sufficient observation period is essential to address these patients’ renal survival. Based on our long follow-up period, we demonstrated that even clinically early IgAN patients can show a progressive disease trajectory in Korea. More than moderate degree of IF and hypoalbuminemia were independent predictors of renal progression. This study is uniquely placed to clarify the prognosis of clinically early IgAN.
Comparisons of definition and outcome of early IgAN with the previous studies
Hong Kong (‘00)
Hong Kong (‘01)
Cr < 1.3 mg/dL
Cr < 120 μmol/L
eGFR > 90 mL/min
eGFR > 60 mL/min
eGFR > 60 mL/min
Proteinuria < 0.4 g/day
Proteinuria < 0.4 g/day
Proteinuria < 0.4 g/day
Proteinuria < 0.5 g/day
Proteinuria < 0.5 g/day
123 (60 –180)
108 (60– 180)
38 ± 16
The divergence in findings may also be explained by racial differences. Recent publications suggest that an Asian racial origin could be identified as a risk for disease progression in IgAN [18, 19]. Despite the fact that our study and the European study enrolled early IgAN patients with similar baseline renal function and proteinuria levels and used similar outcome definitions, renal prognosis in our cohort was considerably different from that observed in the European cohort. To clarify the influence of ethnicity on these observations, a delicate genetic analysis with consideration of phenotype should be performed.
Lead-time bias may also explain the different outcomes in early IgAN. Because of variations in biopsy practices, the disease is detected at different times in its natural course. Even among early IgAN patients with similar initial presentations, the duration of disease could be different. Some patients visit the clinic immediately after gross hematuria or incidentally detected hematuria, while others visit several years after the initial manifestation. However, clinicians can only conduct assessments at the time of initial visit or biopsy. Therefore, a comparison of these patients using only initial data could be limited by lead-time bias.
Our data also showed that pathological changes including IF can be important for renal risk prediction in clinically early IgAN patients. More than 12% of patients showed a more than moderate degree of tubulo-interstitial changes. Furthermore, IF is an independent predictor of ESRD progression in this study. Such results are consistent with some previous studies [9, 20, 21] and inconsistent with another study . Although IgAN is a glomerular disease, tubulo-interstitial injury via the mesangio-podocytic-tubular crosstalk plays an important role in mediating renal fibrosis and, ultimately resulting in, renal failure . In our study, mesangial hypercellularity or interstitial inflammation was not associated with renal progression. Those are considered relatively early renal injury markers, whereas IF is regarded as relatively advanced marker in IgAN patients with minor abnormalities. Indeed, IF is one component of the Oxford classification, although it is validated mostly in patients with proteinuria of more than 1 g/day [23, 24]. Our study results support the applicability of the Oxford classification even in IgAN patients with a minimal clinical presentation.
We further demonstrated that hypoalbuminemia is a significant predictor of renal outcome. These finding is consistent with those in previous IgAN studies [4, 25] as well as those in other CKD studies [26, 27]. Lower serum albumin levels can be explained by the amount of proteinuria, nutritional status or combined inflammation. In our cohort, 7 patients showed reduced serum albumin levels. Their proteinuria amount was ranged between 0.16 and 0.45 g/day. Three patients had combined inflammation, and one patient suffered from tuberculosis and was subsequently malnourished. In other words, hypoalbuminemia may contribute to a poor renal outcome, independently from proteinuria.
The particular strengths and insights gained from this investigation include the long follow-up duration and large sample size, which is specifically important in IgAN research because of the insidious course of this disease. We were able to assess hard outcomes such as ESRD progression and mortality in this study. Moreover, we were able to suggest racial differences in IgAN prognosis by using baseline characteristics and outcome definitions similar to those used in the prior European study. We were also able to alarm many nephrologists and primary physicians who have managed clinically early IgAN patients with ease, especially in Korea.
However, several shortcomings remain to be resolved. First, the number of outcomes observed in our cohort was too small despite the long follow-up duration. Lack of events hampered our ability to perform robust multivariate predictive modeling. Second, this is a single-center, retrospective study, and therefore, we could not take into account diverse management strategies according to individual clinicians. Although hard outcome data were collected by both medical record review and from a national registry or statistics, the last clinical status remains unknown in some cases. Third, we could not use the Oxford classification in this study. However, we were able to measure each component of the Oxford classification semi-quantitatively, as shown in Table 1. Lastly, we could not clarify the precise reason for progression to ESRD among patients with initially benign clinical presentations. We proposed different outcome definitions, lead-time bias, and ethnicity as potential explanations. However, we could not prove these, and further sequential investigation is therefore warranted.
In this study, we demonstrated that clinically early IgAN does not always show a favorable outcome and may even progress to ESRD. Patients with IF and hypoalbuminemia should be more aggressively monitored, especially in Korea.
Estimated glomerular filtration rate
End-stage renal disease
This study was supported by a grant from the Korea Healthcare Technology R&D Project, Ministry for Health and Welfare, Republic of Korea (HI10C2020).
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