Abstract
Objective: This study investigated the relationship between the levels of serum creatinine (SCr), the estimated glomerular filtration rate (eGFR), and the degree of tubulointerstitial injury. Methods: A total of 511 patients of Zhongshan hospital in China were hospitalized due to physical abnormalities and diagnosed with kidney disease by renal biopsy. The clinical and pathological data were retrospectively analyzed. The level of SCr was determined in all patients, and the eGFR was calculated with modification of diet in renal disease and Cockcroft–Gault formulae, whereas the renal histopathology was quantified according to the Katafuchi semi-quantitative standards. Results: With the aggravation of tubulointerstitial injury, SCr level increased and eGFR decreased gradually. The degree of tubulointerstitial lesion showed a positive correlation with SCr level and negative correlation with Cockcroft–Gault formula and modification of diet in renal disease (r = 0.627, −0.649, −0.626; p < 0.001). When the SCr was in the normal range, above 90% of the patients had various degrees of tubulointerstitial damage and 12.2% of the patients had moderate-to-severe tubulointerstitial lesions. The correlation between SCr level and tubulointerstitial damage became weak. Conclusions: The morphologic changes of tubulointerstitium are closely linked with renal function, but incompletely parallel. SCr in the abnormal range could be used to diagnose tubulointerstitial injury well. However, when the level of SCr was in the so-called normal range, eGFR by the modification of diet in renal disease or Cockcroft–Gault formula may be preferred to assess renal tubulointerstitial injury.
INTRODUCTION
Among extraglomerular parameters, the key position is occupied by the relative interstitial volume. In numerous reports, this variable has shown the strongest association with renal function both at the time of biopsy and when there is risk of chronic renal failure.1 Over the last decades, tubulointerstitial injury regardless of the type of glomerulopathy, characterized morphologically by tubular atrophy, interstitial fibrosis, and interstitial inflammation of variable severity, contributed to the progression of renal disease.2 Early literature has documented that the extent of renal dysfunction is poorly associated with changes in glomerular morphology, but it correlates well with chronic tubulointerstitial injury.3–5 At the same time, Bohle et al.4 elucidated that there was a correlation between serum creatinine (SCr) levels and the severity of tubulointerstitial involvement, evaluated by morphometric analysis of renal biopsies of patients with glomerulonephritis (GN), and this trend was demonstrated even in diseases in which the glomerular lesion was predominant. To date, renal biopsy remains the gold method to analyze morphometric changes, whereas multiple biopsies to gauge renal diseases are not feasible because of their invasive nature in health examination every year. SCr is the common predictor of renal function in clinical physical examination,6 but sometimes does not predict the real renal injury because it is easily affected by age, gender, weight, race, diet, medicine, and so forth. Usually, the renal physician estimates the glomerular filtration rate (GFR) from the SCr concentration using Cockcroft–Gault (CG-GFR) and modification of diet in renal disease (MDRD-GFR) formulae. Hitherto, the relationship between SCr concentration, estimated GFR (eGFR), and tubulointerstitial lesion has been not clarified clearly and systematically. The aim of this study is to analyze the correlation of renal basic function and tubulointerstitial lesion in Chinese patients with early physical renal abnormalities.
METHODS
Patients
The patients eligible for this study were hospitalized due to physical abnormalities in Zhongshan hospital from January 2007 to December 2010 and diagnosed with kidney disease by renal biopsy. The eligibility criteria were as follows: (1) physical abnormalities, such as proteinuria and hematuria; (2) a diagnosis of renal disease by biopsy clearly; and (3) no renal disease history.
Laboratory Parameters
Blood samples for measuring SCr, urea nitrogen, and albumin were drawn at the time of renal biopsy. Serum concentrations of creatinine were measured by an enzymatic colorimetric method using a Beckman CX4 automatic biochemistry analyzer (Beckman Coulter Inc., Brea, CA, USA). The normal range of SCr is 44–115 μmol/L as per the standard of clinical laboratory in Zhongshan hospital.
GFR according to the Cockcroft–Gault formula is calculated as follows7: GFR = (140–age) × weight in kg × 0.85 (if female)/(72 × SCr in mg/dL). GFR according to the MDRD equation is calculated as follows8: GFR = 170 × [SCr]0.999 × [age]−0.176 × [SUN]−0.170 × [Alb]0.318 × 0.762 (if female), where SCr is SCr concentration (mg/dL), Alb is serum albumin concentration (g/dL), and SUN is serum urea nitrogen concentration (mg/dL).
Pathology Parameters
The entire biopsy specimens were prepared and examined by clinician and technician. All samples were obtained by percutaneous method using a tricot needle under ultrasound guidance. Three renal biopsy samples were taken from each patient, which were analyzed using light microscopy, immunofluorescence, and electron microscopy. Sections were made from formalin-fixed paraffin-embedded tissue and stained by hematoxylin–eosin, periodic acid Schiff, and Masson’s trichrome stain for light microscopy. Immunofluorescence microscopy panel included staining for IgA, IgM, IgG, C3, C1q, and fibrinogen. Electron microscopic study was performed at the Department of Pathology, Shanghai Medical College, Fudan University. Pathological diagnosis was made for each patient on the basis of both clinical and histological investigations. The tubulointerstitial index was calculated according to the Katafuchi semi-quantitative standards as the sum of individual tubulointerstitial changes,9 including interstitial inflammatory cell infiltration, interstitial fibrosis, and tubular atrophy. Each variable was scored as 0, 1, 2, and 3. The range of tubulointerstitial scores is 0–9. Therefore, the extent of tubulointerstitial lesions was classified as absent (grade 0, 0 score), mild (grade 1, 1–3 score), moderate (grade 2, 4–6 score), or extensive (grade 3, 7–9 score).
Statistical Analysis
The SPSS 16.0 software (SPSS Inc., Chicago, IL, USA) was used for the statistical analysis. Continuous data are presented as means ± SD; the Mann–Whitney test was used for comparison among groups. Categorical data are presented as counts and proportion; χ2-value was calculated by Fisher’s exact probability among groups. For correlation, Spearman’s correlation coefficient was evaluated. The significance level was set at p < 0.05.
Table 1 Pathological diagnosis of renal diseases (N = 511).
Table 2 Clinical characteristics and tubulointerstitial grades of 511 patients.
Table 3 Correlation of tubulointerstitial lesions with SCr, CG-GFR, and MDRD-GFR.
Table 4 Demographic characteristics of tubulointerstitial lesion according to SCr concentrations.
RESULTS
A total of 511 patients eligible for this study were hospitalized due to physical abnormalities and diagnosed with kidney disease by renal biopsy. A total of 511 patients aged 42.05 ± 12.37 years (range 11–81 years; 250 females and 261 males) were included in the study. Table 1 shows the distribution of renal diseases in all the biopsies elected. IgA nephropathy (IgAN) (36.6%, n = 187) is the most prevalent and important glomerular disease among 403 cases of primary GN, and the ratio of primary to secondary GN is 7.20:1 (403/56) in this study.
As shown in Table 2, the most prevalent among the tubulointerstitial lesions of patients selected was grade 1 (60.7%, n = 310) and followed by grade 2 (22.9%, n = 117), grade 3 (10.8%, n = 55), and grade 0 (5.6%, n = 29). Therefore, above one-third patients (n = 172) have already represented moderate-to-severe tubulointerstitial lesions, and most of them are the young people (age: 42.45 ± 13.98 years). There were no significant differences in sex or age among the four groups; however, the mean level of SCr, CG-GFR, and MDRD-GFR among the four groups had statistically significant differences. Tubulointerstitial lesions increased, accompanied by reductions in SCr, MDRD-GFR, and CG-GFR value in patients with renal disease.
In Table 3, the level of SCr examined showed a strong direct correlation with the tubulointestinal lesions (Spearman p = 0.617, r < 0.001). While GFR estimated by the MDRD and the Cockcroft–Gault formulae showed a negative correlation markedly (Spearman r = −0.626; −0.0.649, all p < 0.001, respectively). All the patients in this study were stratified into two groups on the basis of the upper value of SCr normal range (115 μmol/L). As shown in Table 4, the value was <115 μmol/L in 328 patients (64.19%) and ≥115 μmol/L in 183 patients (35.81%). When the SCr was below 115 μmol/L, SCr, MDRD-GFR, and CG-GFR showed a slightly weaker correlation with tubulointerstitial injury than that of the other group, and the former group (328 patients) still experienced tubulointerstitial injury as follows: absence of injury in only 27 patients (8.23%), mild injury in majority (79.57%) of patients, and moderate-to-severe injury in 40 patients (12.20%).
Table 5 Tubulointerstitial lesions of 328 patients (SCr < 115 μmol/L).
When the SCr value was at normal range in 328 cases, 40.55% patients had decreased MDRD-GFR (<90 mL/min/1.73 m2), and had significant difference in tubulointerstitial lesion from normal GFR group (χ2 = 15.638, p < 0.01) (Table 5).
DISCUSSION
The pathological analysis has revealed that in a number of cases the extent of tubulointestinal damage and degree of renal tubular fibrosis correlated better with the deterioration of renal function than the degree of glomerular damage itself.10
Primary GN contributes to the most important and predominant renal disease, meanwhile the type of primary glomerular diseases is unique in its high prevalence of IgAN occurring in China.11 Our epidemiological data have showed that the ratio of primary to secondary GN was 7.20:1 in this special study. The cause of decline in secondary GN could be explained by the fact that physicians have paid more attention to primary diseases prone to progression of kidney, such as systemic lupus erythematosus, metabolic diseases, vascular diseases, and infections, resulting in decreased number of patients with secondary GN selected in this study.
It has been found that tubulointerstitial injury may contribute to the progression and a final common pathway of end-stage renal failure,12 while early diagnosis of renal disease and proper treatment on that can prevent the processes in prospective deterioration of renal function,13 which is significantly associated with morphometric changes in renal biopsy. Schainuck et al.5 also came to the conclusion that the extent of renal dysfunction is poorly associated with changes in glomerular morphology, whereas it correlated well with chronic tubulointerstitial injury in patients with chronic kidney disease in their previous study. Recently,14 similar study suggested a positive correlation between the severity of tubulointerstitial damage and the deterioration of the final SCr.13 We also concluded that the level of SCr, a common predictor of renal function in health examination, correlated with the severity of tubulointerstitial lesions in these patients with first diagnosis of GN or tubulointerstitial diseases.
Tubulointerstitial injury induces a decline in GFR by several mechanisms in which the tubular injury can increase fluid delivery to the macula densa and trigger a reduction in eGFR via tubule glomerular feedback. Our findings indicated that decrease in CG-GFR and MDRD-GFR associated significantly with the extent of tubulointerstitial injury. When the SCr values were normal, there was a decline in MDRD-GFR in 40.54% patients, approximately 12% of whom were found to have moderate-to-severe tubulointerstitial injury. Consistent with this hypothesis, a previous study documented that the impairment of eGFR related better with the extent of tubulointerstitial damage than with the degree of the glomerular damage.5
CONCLUSIONS
We selected numerous special patients who were diagnosed with renal diseases in health examination, representing relatively early diagnosis of various types of kidney disease, and concluded the relationship between the level of SCr, MDRD-GFR, CG-GFR, and renal tubulointerstitial lesions in them. The results would give a hint to physicians, even to the patients, to emphasize on health examination more regularly and carefully than before.
| Item | N | % |
|---|---|---|
| Primary GN | 403 | 78.9 |
| IgAN | 187 | 36.6 |
| FSPGN | 53 | 10.4 |
| MCD | 51 | 10.0 |
| FSGS | 41 | 8.0 |
| MN | 39 | 7.6 |
| MesPGN | 23 | 4.5 |
| Crescentic nephritis | 9 | 1.8 |
| Secondary GN | 56 | 10.9 |
| LN | 17 | 3.3 |
| DN | 15 | 2.9 |
| HSPN | 10 | 2.0 |
| Vascular diseases | 14 | 2.7 |
| Acute interstitial nephritis | 11 | 2.2 |
| Sclerosing glomerulonephritis | 16 | 3.1 |
| Others | 25 | 4.9 |
| Total | 511 | 100.0 |
Note: IgAN, IgA nephropathy; GN, glomerulonephritis; FSGS, focal segmental glomerulosclerosis; MN, membranous nephropathy; FSPGN, focal segmental proliferative glomerulonephritis; MesPGN, mesangial proliferative glomerulonephritis; MCD, minimal change disease; HSPN, Henoch–Schönlein purpura nephritis; LN, lupus nephritis; DN, diabetic nephropathy.
| The grade of tubular injury | ||||
|---|---|---|---|---|
| Item | 0 (score 0) | 1 (score 1–3) | 2 (score 4–6) | 3 (score 7–9) |
| N | 29 | 310 | 117 | 55 |
| M/F | 10/19 | 158/152 | 67/50 | 26/29 |
| Age | 34.03 ± 14.70 | 42.58 ± 14.38 | 43.54 ± 14.55 | 40.15 ± 12.48 |
| SCr | 72.31 ± 48.63 | 92.73 ± 71.84*,*** | 170.02 ± 121.5*,** | 383.02 ± 260.94*,**,*** |
| CG-GFR | 114.93 ± 39.08 | 95.84 ± 32.81*,*** | 58.91 ± 37.31*,** | 29.14 ± 23.31*,**,*** |
| MDRD-GFR | 113.40 ± 41.26 | 90.41 ± 32.48*,*** | 52.64 ± 29.45*,** | 26.00 ± 21.38*,**,*** |
Notes: Comparison with the first group, *p < 0.01; comparison with the second group, **p < 0.01; comparison with the third group, ***p < 0.01. MDRD, modification of diet in renal disease; CG, Cockcroft–Gault; GFR, glomerular filtration rate; SCr, serum creatinine.
| N = 511 | SCr < 115 μmol/L | SCr ≥ 115 μmol/L | ||||
|---|---|---|---|---|---|---|
| Item | r | p | r | p | r | p |
| SCr (μmol/L) | 0.617 | 0.000 | 0.246 | 0.000 | 0.485 | 0.000 |
| CG-GFR (mL/min/1.73m2) | −0.649 | 0.000 | −0.374 | 0.000 | −0.531 | 0.000 |
| MDRD-GFR (mL/min/1.73m2) | −0.626 | 0.000 | −0.300 | 0.000 | −0.520 | 0.000 |
Note: MDRD, modification of diet in renal disease; CG, Cockcroft–Gault; GFR, glomerular filtration rate; SCr, serum creatinine.
| Tubulointerstitial lesion | |||||
|---|---|---|---|---|---|
| SCr (μmol/L) | Grade 0 | Grade 1 | Grade 2 | Grade 3 | Total |
| <115 (n, %) | 27 (8.23) | 261 (79.57) | 37 (11.28) | 3 (0.92) | 328 |
| ≥115 (n, %) | 2 (1.09) | 49 (26.78) | 80 (43.72) | 52 (28.41) | 183 |
| Total | 29 | 310 | 117 | 55 | 511 |
Note: SCr, serum creatinine.
| The extent of tubulointerstitial lesion | |||||
|---|---|---|---|---|---|
| MDRD-GFR (mL/min/1.73 m2) | 0 | 1 | 2 | 3 | Total |
| <90 | 3 | 107 | 21 | 2 | 133 (40.55%) |
| ≥90 | 24 | 154 | 16 | 1 | 195 (59.45%) |
| Total | 27 | 261 | 37 | 3 | 328 |
Notes: χ2 = 15.638, p < 0.01. MDRD, modification of diet in renal disease; GFR, glomerular filtration rate.
ACKNOWLEDGMENTS
We would like to thank Professor ZhiGang Zhang for helping with the electron microscopic investigations. This study was supported by the National Natural Science Funds of China (81000307), the Project of Technology Committee in Shanghai of China (10JC1402900), and the special fund for “211 project” from Chinese Education Department (211XK20).
REFERENCES
- Okon K. Tubulo-interstitial changes in glomerulopathy II Prognostic significance. Pol J Pathol. 2003;54:163–169. [Google Scholar]
- D’Amico G. Tubulo-interstitial damage in glomerular diseases: Its role in the progression of the renal damage. Nephrol Dial Transplant. 1998;13:S80–S85. [Google Scholar]
- Risdon RA, Sloper JC, De Wardener HE. Relationship between renal function and histological changes found in renal biopsy specimens from patients with persistent glomerular nephritis. Lancet. 1968;17:363–366. [Google Scholar]
- Bohle A, Mackensen-Haen S, von Gise H, . The consequences of tubulo-interstitial changes for renal function in glomerulopathies: A morphometric and cytological analysis. Pathol Res Pract. 1990;186:135–144. [Google Scholar]
- Schainuck LI, Striker GE, Cutler RE, Benditt EP. Structural-functional correlations in renal disease. Part II: The correlations. Hum Pathol. 1970;1:631–641. [Google Scholar]
- Shemesh O, Golbetz H, Kriss JP, Myers BD. Limitations of creatinine as a filtration marker in glomerulopathic patients. Kidney Int. 1985;28:830–838. [Crossref], [PubMed], [Web of Science ®], [Google Scholar]
- Cockcroft DW, Gault MH. Prediction of creatinine clearance from serum creatinine. Nephron. 1976;16:31–41. [Crossref], [PubMed], [Web of Science ®], [Google Scholar]
- Levey AS, Bosch JP, Lewis JB, Greene T, Rogers N, Roth D. A more accurate method to estimate glomerular filtration rate from serum creatinine: A new prediction equation. Modification of Diet in Renal Disease Study Group. Ann Intern Med. 1999;130:461–470. [Crossref], [PubMed], [Web of Science ®], [Google Scholar]
- Katafuchi R, Kiyoshi Y, Oh Y, . Glomerular score as a prognosticator in IgA nephropathy: Its usefulness and limitation. Clin Nephrol. 1998;49:1–8. [PubMed], [Web of Science ®], [Google Scholar]
- Yahya TM, Pinngle A, Boobes Y, Pingle S. Analysis of 490 kidney: Data from the united Arab Emirates renal diseases registry. J Nephrol. 1998;11:1480–1507. [Google Scholar]
- Li LS, Liu ZH. Epidemiologic data of renal diseases from a single unit in China: Analysis based on 13,519 renal biopsies. Kidney Int. 2004;66:920–923. [Crossref], [PubMed], [Web of Science ®], [Google Scholar]
- Hsieh C, Chang A, Brandt D, Guttikonda R, Utset TO, Clark MR. Predicting outcomes of lupus nephritis with tubulointerstitial inflammation and scarring. Arthritis Care Res (Hoboken). 2011;63:865–874. [Google Scholar]
- Bohle A, Mackensen-Haen S, von Gise H. Significance of tubulointerstitial changes in the renal cortex for the excretory function and concentration ability of the kidney: A morphometric contribution. Am J Nephrol. 1987;7:421–433. [Crossref], [Google Scholar]
- Rocha KB, Soares VA, Viero RM. The role of myofibroblasts and interstitial fibrosis in the progression of membranous nephropathy. Ren Fail. 2004;26:445–451. [Taylor & Francis Online], [Web of Science ®], [Google Scholar]