Evaluation of Toxic Metals in Blood and Urine Samples of Chronic Renal Failure Patients, before and after Dialysis

Abstract

The determination of toxic elements in the biological samples of human beings is an important clinical screening procedure. The aim of this work was to determine total content of toxic elements—aluminum (Al), cadmium (Cd), and lead (Pb)—in whole blood and urine samples of male chronic renal failure patients (CRFPs) on maintenance hemodialysis from 2006 to 2007. The study included 100 CRFPs, plus 150 healthy volunteers in the control group. The concentration of toxic elements (TEs) were determined in blood sample before and after hemodialysis, while urine sample was determined once, before dialysis. Toxic elements were analyzed by electrothermal atomic absorption spectrometer, prior to microwave-induced acid digestion. The accuracy of the total Al, Cd, and Pb measurements was tested by simultaneously analyzing certified reference materials. No significant differences were established between the analytical results and the certified values (paired t-test at p > 0.05). The levels of TEs in blood samples of patients before dialysis were found to be higher than blood samples after dialysis session. In the control group, the blood levels of Al, Cd, and Pb were significantly lower than the chronic renal failure patients. Moreover, the study shows that analyzing levels of Al, Cd, and Pb may be useful in hemodialysis patients in evaluating TEs status.

Keywords:

• toxic elements
• renal failure
• blood
• urine
• dialysis

INTRODUCTION

Chronic kidney disease is an important cause of morbidity and mortality all over the world. Renal replacement therapy or dialysis in an individual with advanced chronic kidney disease is an important step in medical science. The initiation of dialysis intensely affects quality of life, incurs significant financial costs, and mandates the use of expensive dialysis resources. Other risks include accelerating the loss of residual renal function and dialysis-related morbidities. The negative consequences of initiating dialysis can be especially deleterious in the elderly, who are very sensitive to lifestyle changes and suffer the highest overall complication rates and most shortened life expectancy on dialysis of any age group.[1]

During hemodialysis (HD), essential kidney functions such as the elimination of water and metabolic wastes as well as the correction of the electrolyte and acid/base state, are replaced by the artificial purification system. Elements such as Na⁺, K⁺, Ca⁺⁺, Mg⁺⁺, Cl–, and H⁺ must be kept in a rather narrow physiological range; otherwise, life-threatening events may occur.[2],[3] The kidney is characterized by its ability to compensate for renal damage, and for this reason, classical tests are insensitive, as they only deviate late, when a large part of the nephron mass is already lost.[4] Hence, tools for detecting heavy metal nephrotoxicity must be sensitive enough to detect early events and ideally should reflect subclinical reversible changes.[5] Alterations in blood and tissue concentrations of TEs in the kidney failure patient have been investigated extensively over the last few years.[6],[7]

Aluminum (Al) is one of the most interesting ions, causing intoxication in chronic renal failure patients (CRFPs) due to the altered metabolism of Al in these patients.[8] Al poisoning in CRFPs who are on long-term maintenance hemodialysis is now recognized as contributing to the dialysis encephalopathy syndrome and to dialysis osteomalacia and anemia.[9] It is accepted that long-term ingestion of Al-containing agents can be potentially harmful to dialysis patients.[10]

The exposure of Pb and Cd to humans via environmental pollution replaces Ca and Zn, respectively, by competition with binding sites in biological systems. It is also known that these elements and their compounds can be toxic if their concentrations exceed certain limits.[11],[12] Chronic environmental exposure of toxic elements produces substantial accumulation of Cd and Pb in a number of tissues, notably the liver, kidneys, and bone.[13] For the general population, the main sources of Cd exposure are diet (from contaminated water and crops grown on contaminated soil) and tobacco.[14] Tobacco-related disease originates from the biological consequences of repeated inhalation exposure to numerous toxic constituents in cigarette smoke, which are produced by pyrosynthesis or liberated during combustion. According to WHO, every 10 s, another person dies as a result of tobacco use.[15]

The source of Al, Cd, and Pb in cigarettes is the tobacco leaf grown on polluted soil.[16] Cadmium inhaled through cigarette smoke is more easily taken up by the body than cadmium in food or water. About 40–60 percent of the cadmium inhaled in smoke is absorbed into the bloodstream, as opposed to the 5–10 percent absorbed through foods. Chronic exposure to Cd often causes renal dysfunction.[17] Renal tubular damage caused by Cd is known to be irreversible.[18] Cigarette smokers and people living in contaminated areas have higher level of Cd in blood and urine, but smokers have more than twice as high concentration as non-smokers.[19],[20] Blood Cd generally reflects current exposure, but partly also lifetime body burden.[21]

Chronic exposure to Pb produces hematological, cardiovascular, neurological, and renal adverse effects, most notably progressive tubulointerstitial nephropathy that develops and leads to kidney failure.[22] The level of Pb exposure, which may be associated with early adverse renal effects is uncertain, however, because developing Pb nephropathy is difficult to detect due to the lack of appropriate blood or urinary biomarkers reflecting an early adverse effect on the kidney.[23],[24]

There are several modern techniques for the determination of very low concentrations of TEs in biological samples.[25] The mineralization methods most frequently employed for the analysis of biological samples are wet acid digestion with concentrated acids using either conventional heating or microwave energy for oxidizing the organic matter.[26],[27] The main advantages of microwave digestion are that it requires smaller amount of samples and oxidizing materials, shorter digestion times, and ease of sample handling. The routine analysis of dialysis concentrates for trace and toxic elements is necessary to reduce exposure and health risk.[5]

The aim of this work is to determine three toxic element concentrations in whole blood and urine samples of patients on maintenance hemodialysis with chronic renal failure. The concentrations of these TEs were determined in blood sample before and after dialysis, while urine analysis was completed just once, at each patient visit before dialysis. TEs were analyzed by electrothermal atomic absorption spectrophotometer prior to microwave induced acid digestion. The accuracy of the total Al, Cd, and Pb measurements was tested by simultaneously analyzing certified reference materials.

MATERIALS AND METHODS

Apparatus

The analysis of elements was carried out by means of a double beam Perkin-Elmer atomic absorption spectrometer model 700 (Norwalk, Connecticut, USA) equipped with a graphite furnace HGA-400, pyrocoated graphite tube with integrated platform, an autosampler AS-800, and deuterium lamp as background correction system. The working parameters for the determination of analytes are shown in Table 1. A domestic microwave oven (Pel PMO23, Japan) programmable for time and with a microwave power of 100–900 W, was used for digestion of the samples. Acid-washed plastic (polypropylene) vessels were used for preparing and storing solutions.

Table 1 Measurement conditions for electrothermal atomization AAS

Parameter	Al	Cd	Pb
Lamp current (mA)	10	7.5	7.5
Wave length (nm)	309	228.8	283.3
Slit width (nm)	0.7	1.3	1.3
Cuvette	Tube	Cup	Cup
Common parameters
Sample volume = 10μL analyte +10 μL corresponding modifiers
Background correction = D2 lamp
Carrier gas argon = 200 mL/min

Reagents and Glassware

Analytical grade chemicals and ultra-pure water obtained from ELGA Labwater System (Bucks, UK) were used throughout the experiment. Nitric acid and hydrogen peroxide were analytical reagent-grade from Merck (Darmstadt, Germany). Standard solutions of Al, Cd, and Pb were prepared by the dilution of certified standard solutions (1,000 ppm) of Fluka Kamica (Buchs, Switzerland) corresponding elemental ions. Moreover, matrix modifiers were employed to analyze Al (0.2 mg of Mg(NO₃)₂, Cd (0.001 mg Pd + 0.0015 mg Mg(NO₃)₂) and Pb (0.2 mg NH₄H₂PO₄), which were prepared from NH₄H₂PO₄, Mg(NO₃)₂, and Pd 99.999% Sigma Aldrich (Milwaukee, Wisconsin, USA). All glassware and plastic material used was previously treated for a 24h in 5M nitric acid and rinsed with double distilled water and then with ultra-pure water.

For accuracy of the analytical technique, Clincheck control-lyophilized human urine and human whole blood (Recipe, Munich Germany) were used as certified reference materials.

Sample Collection and Pretreatment

This study involved 100 chronic renal failure (CRF) male smokers, with an age range of 25–55 years, admitted in the urology ward of Liaquat Medical University Hospital, Hyderabad, Pakistan, from 2006–2007. All patients were undergoing maintenance hemodialysis for the previous 6–12 months. One hundred and fifty age-matched healthy subjects who were receiving physical checkup were recruited as the control group. Five to ten samples of blood and urine were collected during the study period from each patient upon hospital admittance for dialysis. We obtained consent verbally and provided information on study objectives, procedures, and implications to participants. The information obtained was demographic characteristics; environmental and occupational data; past or present history of smoking, diabetes, hypertension; and duration of renal problem. At the start of the study, the participants' weight, height, and blood pressure were noted. The dialysis unit had good water treatment devices. The study was approved by the higher education commission of Pakistan.

Blood samples were taken before hemodialysis (BHD) and after hemodialysis (AHD) sessions, while urine samples were taken once BHD. The blood samples were also taken from the patients for the biochemical parameters investigated in clinical laboratories of Liaquat Medical University Hospital (results are also included in present study). Patients with hepatitis B, acute medical events, or aluminum-containing drug usage as well as nonsmokers were excluded from this study. All patients and referents belong to four occupations, as shown in Table 2.

Table 2 Characteristic study of subjects

	Patients n = 100	Controls n = 150
Age	25–55	25–55
Median		(32.0)
Occupation
Agricultural	20 (36)	30 (20)
Fishing	15 (27)	25 (17)
Construction	20 (36)	25 (17)
Industry workers	45 (81)	70 (47)
Smoking habit	100 %	40% smokers

Values in parenthesis is percent of total subjects.

Healthy male referent or control subjects (smoker and nonsmokers) were frequency-matched to the cases by age, geographical area (province Sindh, Pakistan), socioeconomic status, and occupations (mostly relatives of CRFPs). Among the control subjects, we found that 40% were smokers. In the present study, we did not evaluate the relationship of hemodialysis patients with medications, as all patients were matched on drug use and treated with same dialysate solution.

Venous blood (3–5 mL) were sampled by using metal-free Safety Vacutainer blood collecting tubes containing >1.5 mg K₂EDTA obtained from Becton Dickinson, (Becton-Dickinson, Rutherford, New Jersey, USA). The samples were stored at −20°C until required for analysis. The 5 mL blood samples were taken from the patients for the biochemical parameters investigated in the pathological laboratories of hospital.

Morning urine samples (spot test) were collected in an acid-washed, decontaminated 100 mL polyethylene tubes (Kartell1, Milan, Italy) before dialysis. In between sampling sessions, the container is wrapped in a clean polyethylene bag. Urine samples were acidified with ultra-pure concentrated HNO₃ (l% v/v) and kept at −4°C. Prior to sub-sampling for analysis, the sample should be shaken vigorously for 1 min to ensure a homogeneous suspension.

Microwave Acid Digestion (MAD)

A microwave-assisted acid digestion procedure was carried out in order to achieve a shorter digestion time and eliminate matrixes effects. Duplicate samples of 0.5 mL of each blood, 1.0 mL of urine, and replicate five samples of each certified sample of blood and urine were taken in Teflon PFA digestion vessels directly, to which 2 mL of mixture of HNO₃ and 30% H₂O₂ (2:1 v/v) were added and left to stand for 10 min. The vessels were then sealed and placed in a PTFE reactor. This was then heated following a one-stage digestion program (250 W) for 2–3 min. After cooling the digestion vessels in an ice bath for 20 min before opening, the resulting solution was evaporated almost to dryness to remove excess acid, and then diluted to 10.0 mL in volumetric flasks with 0.2 M HNO₃. The validity and efficiency of the microwave-assisted digestion method was checked with certified samples of human hair, urine, and whole blood with those obtained from conventional wet acid digestion method.[28]

Blank extractions (without sample) were carried through the complete procedure of both methods. The concentrations were obtained directly from calibration graphs after correction of the absorbance for the signal from an appropriate reagent blank. All experiments were conducted at room temperature (30–35°C) following well-established laboratory protocols.

Analytical Figure of Merit

Calibration was performed with a series of Al, Cd, and Pb standards. Sensitivity (m) was the slope value obtained by least-square regression analysis of calibration curves based on peak area measurements. The equation (n = 5) for the calibration curves was as follows:

where Y is the integrated absorbance and the concentration range of Al, Cd, and Pb for calibration curve reached from the detection limits up to 200 μg/L, 10 μg/L, and 100 mg/L for Al, Cd, and Pb.

The limits of detection (LOD) and limit of quantification (LOQ) for elements were calculated as respectively, where s is the standard deviation of 10 measurements of the blank, and m is the slope of the calibration graph obtained for each case. The LODs were 10 μg/L, 0.05 μg/L, and 0.5 μg/L, while LOQs were 33.3 μg/L, 0.17 μg/L, and 11.3 μg/L for Al, Cd, and Pb, respectively.

The validation of MAD was evaluated by comparison with the conventional acid digestion of certified reference materials of whole blood and urine (ClinChek®, Control). The paired t-test was also applied to compare the results of each method. The t_experimental values were calculated at degrees of freedom n − 1 = 5, and the experimental values are lower than the t_crit (2.23) at a confidence interval of 95% (p < 0.05), indicating a non-significant difference obtained for Al, Cd, and Pb in blood and urine samples by CAD and MAD (see Table 3).

Table 3 Determination of toxic elements (TEs) in certified blood and urine samples using conventional (CAD) and microwave-assisted acid digestion (MAD)

TEs	Certified values	CAD	MAD	Paired t test,tExperimental	% Recovery
Blood (μg/L)
Al	—	221 ± 20.6	215 ± 16.7	0.0622	97.5
Cd	1.2 ± 0.4	1.2 ± 0.065	1.19 ± 0.054	0.0456	99
Pb	105 ± 24	104 ± 5.8	103 ± 5.5	0.127	98
Urine (μg/L)
Al	—	4.65 ± 0.45	4.60 ± 0.35	0.140	98.8
Cd	11.8 ± 2.5	11.8 ± 0.74	11.8 ± 0.77	0.061	99.4
Pb	41 ± 9.9	40.9 ± 2.87	40.5 ± 2.79	0.134	99.0

*Paired t-test between MAD versus CAD, degree of freedom 4 = (n −1).

t_Critical at 95% CL = 2.23.

Statistical Analysis

Data were expressed as mean ± SD and analyzed with Minitab program (version 13.2). A comparison of the toxic elemental contents in renal failure patients vs. controls with normal renal function was done using the T-test. The statistical significant differences (p < 0.05) were observed between the results of the TEs in the biological samples of normal subjects (whole blood and urine) and CRFPs of two categories, pre- and post-dialysis. A p value less than 0.05 was considered to be significant.

RESULTS

Methodology

The conventional wet acid digestion method was very efficient because the percentage recovery of toxic metals in the certified sample was found to be up to 98.04–100% as compared to certified values, but it was time-consuming. The microwave-assisted digestion method was efficient, and only 3–5 min were required for complete digestion of both biological samples. The overall recoveries of Al, Cd, and Pb in certified biological samples by using the microwave digestion method are 97–99%. Mean values of Al, Cd, and Pb differed by 1–3% from the certified values. Non-significant differences were observed for p > 0.05 when comparing the values obtained by both methods (paired t-test; see Table 3).

Biochemical Parameters of Chronic Renal Failure Patients (CRFP)

Biochemical data concerning the CRFPs on maintaining hemodialysis and control groups obtained from the pathological laboratories of hospital are shown in Table 4.

Table 4 Biochemical parameters of chronic renal failure patients (before (BHD) and after hemodialysis (AHD)) and controls

Parameters	Normal range	Healthy controls	Pre-dialysis	Post-dialysis
Hemoglobin (g/dL)	12–18	11.67 ± 0.67	8.12 ± 0.91	7.55 ± 0.87
Creatinine (mg/dL)	0.6–1.3	0.95 ± 0.056	1.50 ± 1.11	0.98 ± 0.055
Blood urea nitrogen (mg/dL)	7–18	12.34 ± 1.23	16.5 ± 1.6	14.2 ± 1.2
Total cholesterol (mg/dL)	140–310	182.3 ± 12.3	155 ± 23.5	142 ± 19.3
Triglyceride (mg/dL)	35–106	102.3 ± 54.4	140 ± 12.3	120 ± 10.4
High-density lipoprotein (mg/dL)	27–89	50.5 ± 4.12	30.12 ± 6.11	45.7 ± 4.3
Creatinine clearance (mL/min)	28–31.5	29.7 ± 1.56	36.6 ± 2.51	33.5 ± 2.42

In order to clarify the role of TEs in CRFPs, the levels of hemoglobin in CRFPs before hemodialysis (BHD) were 7.02% higher than after hemodialysis dialysis (AHD) at p < 0.05, though significantly lower than controls (p = 0.002). Blood urea nitrogen and total cholesterol were also measured BHD and immediately AHD. The mean creatinine clearance in urine samples of the control group was observed as 29.7 ± 1.56 mL/min; however, the creatinine clearance was significantly increased in CRFPs (36.6 ± 2.51 mL/min), and 7.0–9.0% lower values were observed in AHD (33.5 ± 2.42 mL/min). Total cholesterol (mg/dL) in BHD was 155 ± 23.5, higher than those observed for AHD (142 ± 19.3), but the levels were significantly lower when compared to that in the healthy controls (p < 0.001). Blood urea nitrogen in BHD (16.5 ± 1.6) was 25% higher than control subjects at p > 0.05. The blood creatinine level in BHDPs (1.50 ± 1.11 mg/dL) was 35% higher as obtained in AHDPs. Triglyceride (140 ± 12.3 mg/dL) in blood samples of BHDPs was significantly higher than controls at p < 0.050, while in AHDPs, a lower amount of triglycerides was observed (120 ± 10.4 mg/dL).

Toxic Elements in Biological Samples of Study Population

The CRFPs form a high-risk group for TEs poisoning, and biological monitoring is indicated to diagnose and prevent toxicity. The results reported in Table 5 show that the concentrations of Al were altered in the biological samples (whole blood and urine) of CRFPs related to control male subjects.

Table 5 Toxic elements (TEs) in blood and urine samples of controls and chronic renal failure patients (CRFPs)

TEs	Controls		CRFPs
	Non-smokers	Smokers	Before dialysis	After dialysis
Whole blood (μg/L)
Al	113 ± 8.9	182 ± 15.3	302 ± 19.5	220 ± 25.1
Cd	1.44 ± 0.8	2.47 ± 1.4	6.22 ± 1.24	4.07 ± 1.53
Pb	182 ± 10.2	214 ± 12.2	347 ± 34.2	237 ± 13.5
Urine (μg/L)
Al	2.04 ± 0.80	5.05 ± 0.43	11.5 ± 6.5	—
Cd	3.86 ± 1.40	6.37 ± 1.24	10.0 ± 3.8	—
Pb	2.43 ± 0.63	5.19 ± 1.32	9.71 ± 4.6	—

The level of Al was significantly higher in whole blood samples of BHDPs at 95% confidence interval [CI: 278.9, 324.0] as compared to blood samples collected from AHDPs [198.92, 240.89] vs. control male subjects [CI: 105, 115 for nonsmokers; 161, 202 for smokers]. Al levels in urine samples of CRFPs [CI: 8.51, 14.3] were higher than those of controls (nonsmokers and smokers) [CI: 1.56, 2.52 and 4.72, 5.43], respectively, at p = 0.020.

In whole blood samples of BHDPs, average Cd concentration was observed at 95% interval [CI: 5.45, 6.99] as compared to AHDPs [CI: 3.36, 4.78], while controls (non-smokers and smokers) have lower Cd concentrations [CI: 1.33, 1.56 and 2.15, 2.79], respectively. We observed a significantly higher (p > 0.008) concentration of Cd in whole blood of control (smoker) as compared with nonsmoker controls. The concentrations of Cd in urine samples of CRFPs at 95% confidence limit [CI: 9.64, 10.5] were greater compared to controls (nonsmokers and smokers) [CI: 3.42, 4.30 and 5.73, 7.01 ], respectively. We observed a significantly higher (p > 0.006) concentration of Cd in urine of smoker controls as compared with nonsmoker controls.

The impact of different occupation on the concentration of Cd in biological samples of CRFPs and referents was not observed except in the case of industrial workers of steel mill and battery manufacturing, who had a high level of Cd in whole blood samples of both patients and controls (p > 0.02). This is also consistent with previous research.[29] The correlation coefficient of Cd in whole blood samples of CRFPs with control (nonsmoker) (r = 0.326, p > 0.03) was found to be lower than those obtained for smokers control (r = 0.443, p > 0.007). In whole blood samples, the concentration of Pb in CRFPs [CI: 311, 388] was greater than blood samples of AHDPs [CI: 200, 263] vs. control (nonsmokers and smokers) [CI: 157, 209 and 190, 236] at 95% confidence limit. A lower concentration of Pb was found in urine samples of controls (nonsmokers and smokers) [CI: 2.04, 2.81 and 4.64, 5.74] versus CRFPs [CI: 8.36, 11.1].

DISCUSSION

The trace and toxic elements occur in very low concentrations in the body, but their role in the maintenance of undisturbed biological functions is very important. In CRFPs, the concentrations of trace elements are modified partly as a consequence of endogenous toxicities and impaired renal function, dietary restriction, and therapeutic measures. Renal toxicity may be caused by acute and subacute exposure to TEs. A number of TEs, as well as dust, fumes, and gases, are found in the working environments. The exposure may have both acute and long-term health effects.[30]

As observed in our study, a higher level of all three TEs was found in both biological samples of CRFPs as compared to age-matched control subjects. The high prevalence of Al, Cd, and Pb toxicity in our hemodialysis patients are consistent with previous research.[31] The sources of TEs abnormalities in HDPs are possible due to the environment, food, and smoking tobacco.[32] The possibility of TEs contamination of various medications and its effects on the metabolism of TEs are still unknown. A recent study had suggested that lipid peroxidation in patients may be due to essential trace element disturbances and that there is a relation between trace elements deficiency and antioxidant levels.[2] In CRF patients, disturbances in enzymatic mechanisms of free radical detoxification lead to an alteration in the antioxidant system, and an ROS (reactive oxygen species) attack on cell membranes also results in the formation of lipid peroxidation products.[33] In vitro and in vivo studies suggested that Pb-induced oxidative damage contributes to red blood cell damage.[34] This was supported by several human studies where the disrupted pro-oxidant/antioxidant balance was demonstrated in Pb- and/or Cd-exposed workers.[35],[36] The importance of this pro-oxidant/antioxidant imbalance was, however, not completely clarified by means of correlating the oxidative damage endpoints with the clinical outcomes of Pb and/or Cd poisoning.

The level of Al was high in CRFPs because in Pakistan, most of the food products (rice, bread, soft drinks, and juices) contained high levels of Al.[37] Normally, the digestive tract is an effective barrier against gastrointestinal aluminum absorption, and most of that which is ingested is excreted unabsorbed in the feaces. What little is absorbed is soon excreted in the urine, although some if it may also be retained in the skeleton. However, the protective function of the intestinal barrier is less effective in the end stage of renal disease patients than healthy individuals.[38]

Due to poverty and unawareness, poor people used alum for water purification. People who have a normal urological system may be not affected significantly, but in those with renal disorders, the toxicity due to Al can become severe. About twenty patients (4% of total) had a concentration (350 μg/L); at this level, dialysis dementia and aluminum bone disease may be developed. Among our study patients group, ten hemodialysis patients (2%) who are also diabetic developed fatal dialysis dementia, and they died during our study period. Al-induced damage to body organs has already been reported in several studies, and accumulation in the kidney has been related to worsening renal function.[39] Indeed, the kidney may be exposed to high concentrations of Al during the normal process of excretion and is therefore a site for Al-mediated toxicity.[40]

In addition to CRFPs, the control smokers had a significantly higher level of Cd in blood samples (p < 0.005) compared to the non-smoker controls. The high prevalence of Cd intoxication in our study smoker patients is proved because the high content of Cd in tobacco and the extent of environmental pollution are suggestive of a connection with smoking. Smoking is an important source of Cd exposure: one cigarette contains 1–7 μg of the metal.[41] On average, about 10% of this amount is inhaled during smoking. Cigarette smoking increases the risk of renal carcinoma: for smokers, there is twice the risk for renal carcinoma and about four times the risk for renal pelvis cancer than for non-smokers.[42] The high level of Cd in food commodities and drinking water is also one of the sources of Cd in our patients, most likely from rice and vegetables grown in soil dressed with untreated industrial waste water sludge.[43] During the past decade, several studies on the health effects of environmental exposure to Cd have shown that tubular effects occur at urinary cadmium concentrations of 1–2 mg/g creatinine.[44]

As in our investigated results, a high level of Pb was observed in biological samples of CRFPs as compared to control subjects. Lead poisoning is determined by the results of a blood test.[45] The normal range for lead in whole blood is >100 μg/L; intervention is usually required when levels reach between 100–140 μg/L.[46] Signs of lead toxicity include central nervous system effects, peripheral neuropathy, hematological abnormalities, and infertility. A recent epidemiological study has linked blood lead levels in the range of 70–400 μg/L with evidence of toxicity in the adults, such as neurobehavioral decrements and renal impairments.[47] The total body burden of lead may be divided into at least two kinetic pools, which have different rates of turnover. The largest and kinetically slowest pool is the skeleton, with a half-life of more than 20 years; the soft tissue pool is much more labile. Lead in bone may contribute as much as 50% of blood lead, so it may be a significant source of internal exposure to lead.[48]

Due to poverty and unawareness, about 30% of CRFPs were diagnosed and referred to nephrologists at last stage of disease, resulting in poorer clinical status at the time of dialysis initiation. These factors are known to adversely affect long-term dialysis for late-referred patients, so a proportion of morbidity and mortality of patients on dialysis may be increased. The effect of late referral CRFPs is also consistent with other research.[49] It was also observed in our study that the CRFPs did not regularly attend the hospital for dialysis, especially low-income people belonging to rural areas, so the mortality rate is very high in these cases. Malnutrition and the associated morbidity and mortality are prevalent in the dialysis population. In our study, it was observed that patients from poor families may have anorexia, social and financial problems, lethargy, and depression due to malnutrition resulting from poor energy intake and an inadequately balanced diet in the predialysis stage. These factors also consistent with previously reported studies.[50],[51] Most often, the patients diagnosed as CRFPs were dying within a six-month to two-year period. Thus, all of the above-mentioned TEs values were used as a sensitive indicator, together with biochemical and classical clinical tests, in the diagnosis of patients with renal disorders.

CONCLUSION

On the basis of the results obtained in this study, a high content of analytes under study in biological samples of CRFPs, as compared to healthy controls, indicates the possible pathological role of these TEs in renal failure. The concentration of TEs in hemodialysis patients before and after the dialysis session must be investigated more extensively to clarify the changes in their concentration during the dialysis session.

There is a need to strengthen the initiative to reduce exposure of TEs (Al, Cd, and Pb), sources such as tobacco smoke, Al-based bakery products, alum-treated water, and food products containing high level of TEs (rice, wheat, vegetables, and tea). The successful prevention of renal diseases induced by occupational or environmental exposure to TEs largely relies on the capability to detect nephrotoxic effects at a stage when they are still reversible or at least not yet compromising renal function.

DECLARATION OF INTEREST

The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.