|Year : 2018 | Volume
| Issue : 3 | Page : 96-102
Beta-trace protein as an early predictor of diabetic nephropathy in type II diabetes
Hayam A Hebah1, Essam N Afifi1, Shaimaa Z Abd El-Megeid1, Mai M Al-Raddad2
1 Nephrology Department, Faculty of Medicine, Ain Shams University, Cairo, Egypt
2 Damietta Governorate Hospital, Damietta, Cairo, Egypt
|Date of Submission||23-May-2018|
|Date of Acceptance||05-Aug-2018|
|Date of Web Publication||09-Nov-2018|
Hayam A Hebah
Nephrology Department, Faculty of Medicine, Ain Shams University, PO box: 11566, Abbasia Square, Cairo
Source of Support: None, Conflict of Interest: None
Background Diabetic nephropathy (DN) represents the leading cause of end-stage renal disease worldwide. Albuminuria is still the standard for diagnosis of DN, although it is limited by the fact that structural damage might precede albumin excretion. So, new biomarkers are needed to predict DN even in patients with normoalbuminuria.
Aim To assess serum beta-trace protein (BTP) level and its possible role in early detection of DN.
Patients and methods This is a prospective cohort study carried on 40 type II diabetic patients with urinary albumin/creatinine ratio less than 30 mg/g and 10 healthy nondiabetic controls without renal disease. Serum BTP and urinary albumin/creatinine ratio were measured for all participants at selection and after 3 months.
Results BTP was significantly higher at selection time in 32/40 (80%) diabetic patients, with median (interquartile range) values of 410 (312.5) ng/ml when compared with controls, with median (interquartile range) of 200 (110) ng/ml (P<0.001). BTP at a cutoff value of 260 ng/ml for the detection of DN, with area under curve of 0.848 and 95% confidence interval of 0.726–0.969, had 80% sensitivity, 80% specificity, 94.1% positive predictive value, and 50% negative predictive value. After 3 months, BTP increased in diabetics to 440 (502.5) ng/ml, with P value of 0.867, and increased in controls to 275 (115) ng/ml, with P=0.007. After 3 months, BTP level positively correlated with blood urea in diabetics (r=0.321, P=0.043).
Conclusion Serum BTP is a predictive marker of DN with high sensitivity and specificity. It detects renal injury earlier than albuminuria. Further studies are needed to assess its relation to glycemic control and disease progression.
Keywords: beta-trace protein, diabetic nephropathy, urinary albumin/creatinine ratio
|How to cite this article:|
Hebah HA, Afifi EN, Abd El-Megeid SZ, Al-Raddad MM. Beta-trace protein as an early predictor of diabetic nephropathy in type II diabetes. J Egypt Soc Nephrol Transplant 2018;18:96-102
|How to cite this URL:|
Hebah HA, Afifi EN, Abd El-Megeid SZ, Al-Raddad MM. Beta-trace protein as an early predictor of diabetic nephropathy in type II diabetes. J Egypt Soc Nephrol Transplant [serial online] 2018 [cited 2019 Mar 21];18:96-102. Available from: http://www.jesnt.eg.net/text.asp?2018/18/3/96/245125
| Introduction|| |
Diabetic kidney disease (DKD) is a major microvascular complication of diabetes characterized by increasing albuminuria and progressive loss of kidney function. Assessment of albuminuria is the gold standard for predicting DKD onset and progression .
Diabetic nephropathy (DN) affects approximately one-third of all diabetic individuals (with either type 1 or type 2 diabetes), which produces significant social and economic burdens .
There are limitations in using albuminuria as a marker of DN, as patients may experience reduction or even loss of glomerular filtration rate (GFR) without deterioration in albuminuria and even with normoalbuminuria .
Furthermore, low-grade albuminuria is a lesser predictor of disease progression than macroalbuminuria. Therefore, there is interest in finding biomarkers to detect DKD earlier and identify progression risk .
Beta-trace protein (BTP), also known as lipocalin prostaglandin D2 synthase, is a novel low-molecular-weight glycoprotein  that is being investigated for its use as a marker of GFR. It exhibits similar advantages to cystatin C over serum creatinine, being independent of height, sex, age, and muscle mass, and showing increased sensitivity, particularly in the creatinine blind range . It is increased in cases of increased glomerular permeability owing to glomerular capillary lesion. Urinary excretion of BTP can be used as a marker of kidney damage alternative to albuminuria as it may detect renal injury earlier than albuminuria because of its lower molecular mass, its constant production rate, its ionic property, and its stability .
BTP is an important constituent of cerebral spinal fluid and is found in much lower concentration in blood . BTP is almost completely excreted via the kidneys .
The aim of this study was to assess serum BTP level and its possible role in early detection of DN in normoalbuminuric type II diabetic patients.
| Patients and methods|| |
This is a prospective study carried out on 40 normoalbuminuric type 2 diabetic patients more than 18 years old with normal serum creatinine and urinary albumin/creatinine ratio (UACR) less than 30 mg/g. They were compared with 10 apparently healthy control participants with no history of diabetes mellitus or kidney disease. Written informed consent was obtained from all patients.
Patients with type I diabetes, UACR more than 30 mg/g, unstable kidney function or kidney disease other than DN, hypertension, pregnancy, malignancy, infections, cerebritis, meningitis, brain tumors, liver disease, or any inflammatory conditions were excluded.
All patients was subjected to detailed history taking, clinical examination, BMI calculation as weight (kg)/height (m)2, overnight fasting for measurement of fasting blood sugar and glycosylated hemoglobin (HbA1c), serum creatinine and urea, and estimated glomerular filtration rate (eGFR) calculation by Modification of Diet in Renal Disease abbreviated equation: [GFR=186×(serum creatinine)−1.154×(age)−0.203×(0.742 if female)×(1.210 if African American)].
UACR and serum BTP were assessed twice, on selection and after 3 months.
Serum beta-trace protein measurement
Overall, 4 ml of venous blood samples was withdrawn. Serum was collected by serum separator tube, where the samples were allowed to clot for 2 h at room temperature or overnight at 4°C before centrifugation for 15 min at 1000g. The serum was removed and assayed immediately or aliquoted and stored at −20°C. Serum BTP was measured by ELISA kit based on double-antibody sandwich enzyme-linked immunosorbent assay technology.
The protocol was approved by the ethics committee of our institution before the study began, and it conformed to the ethical guidelines of the 1975 Helsinki Declaration.
Data were collected, revised, coded, and entered to the statistical package for the social science, version 20 (SPSS Inc., Chicago, Illinois, USA). The qualitative data were presented as number and percentage, whereas quantitative data were presented as mean with SD or median with interquartile ranges (IQR) for nonparametric data (UACR1, BTP1, and BTP2). Comparison between two groups with qualitative data was done by using χ2-test. Fisher exact test was used for qualitative data. Comparison between two groups with quantitative data was done by independent t-test when the distribution of the data was found parametric. Mann–Whitney test and Wilcoxon signed test were used with the nonparametric data. Spearman correlation coefficients were used to assess the correlations. The study power by post-hoc calculator is 97.5%.
The P value was considered significant as follows:
- P>0.05: nonsignificant.
- P<0.05: significant.
- P<0.01: highly significant.
| Results|| |
Our study included 40 (25 males and 15 females) diabetic patients of average age 47.58±8.35 years. They were diabetics for an average of 56.4±13.24 months. Of the 40 diabetic patients, 33 patients were smokers and 32 (80%) were using metformin and sulfonylurea, whereas eight (20%) were using metformin only. Diabetic patients had higher BMI, fasting blood sugar, HbA1c, blood urea, and serum creatinine and lower eGFR (81.29±17.94 vs. 111.38±15.75 ml/min/1.73 m2, P≤001) than the control group, but were matched in age, sex, and mean arterial blood pressure (MABP) at baseline, as shown in [Table 1].
|Table 1 Comparison between diabetic cases and control regarding some demographic, clinical, and laboratory data|
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Receiver operator characteristic curve (ROC) curve revealed that at the serum BTP cutoff value of 260 ng/ml, with area under curve (AUC) of 0.848 and 95% confidence interval of 0.726–0.969 ([Figure 1]), it had a sensitivity of 80% and specificity of 80% with positive predictive value (PPV) 94.1% and negative predictive value (NPV) 50%. The cutoff value of UACR was 4.015 mg/g, with 95% confidence interval of 0.648–0.912, and for serum creatinine was 0.805 mg/dl, with 72.5% sensitivity and 80% specificity for both, with PPV 93.5% and NPV 42.1% ([Table 2] and [Table 3]).
|Figure 1 ROC curve of creatinine, urinary albumin/creatinine ratio (UACR), and beta-trace protein (BTP).|
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|Table 2 ROC curve of creatinine, urinary albumin/creatinine ratio and beta-trace protein in diabetic kidney disease prediction|
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|Table 3 Sensitivity, specificity, positive predictive value, and negative predictive value of markers of diabetic kidney disease|
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At the time of selection, BTP was more than 260 ng/ml in 80% of diabetic patients. After 3 months, only 70% of cases had BTP more than 260 ng/ml, despite BTP levels having increased from median 410 ng/ml to median 440 ng/ml. In control participants, only 20% had BTP more than 260 ng/ml at selection. After 3 months, the frequency increased to be 70% with BTP more than 260 ng/ml ([Table 4] and [Table 5]).
|Table 4 Comparison between diabetic cases and controls regarding urinary albumin/creatinine ratio and beta-trace protein at selection|
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|Table 5 Comparison between diabetic cases and controls regarding urinary albumin/creatinine ratio and beta-trace protein after 3 months|
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In this study, there was a significant statistical difference between both diabetic patients and controls at time of selection regarding UACR and BTP, with P value of 0.007 and 0.001, respectively. After 3 months, there was still significant statistical difference between diabetics and controls, with P values of 0.015 and 0.002, respectively, for comparison between UACR2 and BTP2 ([Table 4] and [Table 5]).
BTP also had higher levels in diabetic cases and control participants after 3 months, with median (IQR) values of 440 (502.50) and 275 (115) ng/ml, respectively, when compared with its levels at time of selection in the same groups, with P values of 0.867 and 0.007, respectively ([Table 6] and [Table 7]). The MABP in diabetics showed nonsignificant statistical rise after 3 months, 116.3±7.614 versus 118.2±5.602 mmHg (P=0.116). In controls, the difference regarding MABP was also nonsignificant (P=0.096). The UACR showed lower values but was statistically insignificant, whereas the HbA1c was lower and statistically significant (P=0.014; [Table 6]).
|Table 6 Comparison between urinary albumin/creatinine ratio, beta-trace protein, fasting blood sugar, glycated hemoglobin, and arterial blood pressure in diabetic cases at the time of selection and after 3 months|
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|Table 7 Comparison between urinary albumin/creatinine ratio and beta-trace protein in controls at time of selection and after 3 months|
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In diabetic cases, at time of selection, BTP did not show any correlation with the studied parameters, whereas after 3 months, it was positively correlated to blood urea only (P=0.043; [Figure 2]).
|Figure 2 Positive correlation between beta-trace protein (BTP)2 and serum urea in diabetic cases.|
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| Discussion|| |
Although the GFR is considered to be the golden standard to measure renal function, there are some limitations for using creatinine as a biomarker of this GFR, and therefore new alternative biomarkers are being investigated, such as low-molecular-weight proteins . BTP is a member of the lipocalin family of proteins and has a low molecular weight. Recently, a lot of interest has grown in studying BTP as an alternative to serum creatinine for evaluating renal function as well as being a biomarker for cardiovascular diseases .
There is paucity of data on the value of serum BTP in different stages of nephropathy in type II diabetic patients. The purpose of this study was to assess serum BTP level and its possible role in early detection of DN.
Our study showed that the best cutoff value of serum BTP was 260 ng/ml, with AUC of 0.848 and 80% sensitivity and 80% specificity with PPV 94.1% and NPV 50%. According to this cutoff value, 80% of our diabetic patients have BTP more than 260 ng/ml [median (IQR) 410 (312.5) ng/ml] whereas 20% of control participants have BTP more than 260 ng/ml [with median (IQR) 200 (110) ng/ml] at selection time. There was a significant statistical difference between diabetic cases and control (P=0.001) even when they all have normoalbuminuria with UACR less than 30 mg/g. Kobata et al.  showed the relationship between stages of DN and BTP serum levels and found that BTP starts to be significantly higher in macroalbuminuric patients without high serum creatinine. There was no statistical difference between controls, normoalbuminuric, or microalbuminuric groups in their work.
There are no available studies that determine the cutoff value of serum BTP in diabetic patients, and the available study by Dajak et al.  was on patients with CKD, whether diabetics or nondiabetics. In their study, the cutoff value of serum BTP in patients with eGFR less than 90 ml/min/1.73 m2 was set to be 650 ng/ml with AUC 0.917, and it showed sensitivity and specificity of 92.9 and 76.2%, respectively. This difference may be attributed to the studied population (diabetic and nondiabetic patients); in addition, serum BTP was measured by a different method (a latex particle-enhanced immunonephelometric assay). Kobata et al. , found that mean±SD serum BTP was 0.475±70.135 mg/dl in 68 normoalbuminuric diabetic patients. This level increased in progressive stages of DN. In their work, serum BTP in controls was 0.460±0.130 mg/dl. They concluded that levels of serum BTP can predict the early prognostic stage of patients with type 2 DN.
Uehara et al. , in their cross-sectional prospective multicenter study, discussed the role of urinary BTP in prediction of renal injury in type 2 diabetic patients. AUC of urinary BTP was 0.840, with sensitivity and specificity of 67 and 93%, respectively. Our results also revealed that serum BTP AUC was 0.848, which is near to the urinary BTP AUC of 0.840, which means that the values of serum BTP and urinary BTP AUC were very close to each other, with higher sensitivity in serum BTP, which is easier in measurement than urinary BTP. So serum BTP is a sensitive marker comparable to the urinary one.
In our study, when comparing between diabetic cases and control at selection time regarding UACR, it was found to be significantly higher in diabetics with median (IQR) of 7.47 (9.382) mg/g than the control with median (IQR) of 3.2 (2.815) mg/g (P=0.007), despite both groups being normoalbuminuric. Other studies6 involving the study of urinary BTP in normoalbuminuric type 2 diabetes mellitus patients also found statistical significant difference in UACR between patients with high and low urinary beta trace protein (UBTP) (UBTP >4.2 and <4.2 mg/g). The patients who had higher UBTP had higher UACR, with median 14.8 (0.8–29.7) mg/g, than the patients with low UBTP, with median UACR of 8.1 (0.4–25.2) mg/g, with P-value less than 0.001, despite both values being within normal range of UACR.
We found that after 3 months, BTP was getting higher median values in both diabetic cases and control. Overall, 70% of diabetic patients had BTP more than 260 ng/ml, with median (IQR) of 440 (502.5) ng/ml, whereas 70% of control participants had BTP more than 260 ng/ml, with median (IQR) of 275 (115). There was a significant statistical difference among patients (P=0.002) and among controls (P=0.007). This can be explained by the elevation of MABP in both diabetic cases and control after 3 months. This elevation of MABP was insignificant in diabetic cases, with P value of 0.116, and insignificant in control, with P value of 0.096, and it was not apparent also in statistical correlations. Some studies reported that elevation of serum BTP is correlated to rise in arterial blood pressure even if they have apparent normal kidney functions . We did not show this correlation in our work.
In our study, UACR median values were getting lower in diabetic cases after 3 months of follow-up. This can be explained by the decline in HbA1c values after 3 months indicating better diabetic control (P=0.014).
We found that serum BTP was positively correlated with blood urea (P=0.043), but the explanation behind this is unclear, and there are no reported similar findings.
| Conclusion|| |
Serum BTP is a promising biomarker with high sensitivity and specificity for early detection of DN in type 2 diabetes mellitus before the development of microalbuminuria and elevation of kidney functions. Further studies with longer follow-up period are needed to assess its relation to glycemic control and kidney disease progression.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7]