|Year : 2013 | Volume
| Issue : 2 | Page : 98-104
Kidney injury molecule-1 as an early marker for acute kidney injury in critically ill patients
Ibrahim M Boghdady1, Mostafa M EL Naggar1, Mahmoud M Emara1, Rania M EL-Shazly2, Karim S Mahmoud1
1 Department of Internal Medicine, Faculty of Medicine, Menoufia University, Menufia, Egypt
2 Department of Medical Biochemistry, Faculty of Medicine, Menoufia University, Menufia, Egypt
|Date of Submission||18-Feb-2013|
|Date of Acceptance||04-Jul-2013|
|Date of Web Publication||31-Jan-2014|
Karim S Mahmoud
MBBCh, 117 Rageb Basha street, Tanta, Gharbia 31111
Source of Support: None, Conflict of Interest: None
The aim of this study was to evaluate the role of kidney injury molecule-1 (KIM-1) as an early marker for acute kidney injury (AKI) in critically ill patients as compared with conventional markers (e.g. serum creatinine).
Depending on traditional markers for renal functions, namely, blood urea and serum creatinine, has led to unacceptable delay in the diagnosis of AKI and in initiating treatment.
Materials and methods
This study included 89 individuals: 79 critically ill patients and 10 healthy individuals who served as controls. All patients were prospectively followed up from the time of ICU admission. Blood and urine samples were collected simultaneously at predetermined time points: at the time of ICU admission, 6 h after arriving, 12 h after arriving, and daily thereafter for a minimum of the next 2 days and a maximum of 5 days.
KIM-1 can detect AKI as early as 6 h from its occurrence and before the elevation of conventional markers. KIM-1 is (unlike conventional markers) not influenced by age, sex, and BMI.
KIM-1 is a reliable indicator for early detection of AKI in critically ill patients.
Keywords: Acute kidney injury, critically ill patients, ICU, kidney injury molecule-1, serum creatinine, serum urea
|How to cite this article:|
Boghdady IM, EL Naggar MM, Emara MM, EL-Shazly RM, Mahmoud KS. Kidney injury molecule-1 as an early marker for acute kidney injury in critically ill patients. Menoufia Med J 2013;26:98-104
|How to cite this URL:|
Boghdady IM, EL Naggar MM, Emara MM, EL-Shazly RM, Mahmoud KS. Kidney injury molecule-1 as an early marker for acute kidney injury in critically ill patients. Menoufia Med J [serial online] 2013 [cited 2018 Mar 19];26:98-104. Available from: http://www.mmj.eg.net/text.asp?2013/26/2/98/126131
| Introduction|| |
Acute kidney injury (AKI) is well recognized for its impact on the outcome of patients in ICUs. The Acute Physiology age and Chronic Health Evaluation version III scoring system and the Sequential Organ Failure Assessment score are two scales that are used to measure the severity of acute illness. Kidney dysfunction is markedly represented in both of them (20 and 16.6% of the total scores, respectively)  .
AKI is generally defined as 'an abrupt and sustained decrease in kidney function'. Until recently there has not been a consensus on which markers best reflect kidney function and what values of those markers discriminate normal from abnormal kidney function  .
Kidney injury molecule-1 (KIM-1) is a type I cell membrane glycoprotein that is associated with proximal tubule cell injury  .
Presence of KIM-1 in the urine is highly specific for kidney injury. No other organ has been shown to express KIM-1 to a degree that would influence kidney excretion. It has been shown to be much more sensitive than creatinine as a marker for AKI  .
This work aims at evaluating the role KIM-1 as an early marker for AKI in critically ill patients as compared with conventional markers (blood urea and serum creatinine).
| Participants and methods|| |
This study included 89 individuals: 79 critically ill patients and 10 healthy individuals who served as controls. Fifty were male and 39 were female and their ages ranged from 25 to 81 years.
They were divided into three groups.
Group 1 (the AKI group)
This group included 44 acute critically ill patients who were admitted to Menoufiya University Hospital and developed AKI during hospitalization. The group comprised 25 male and 19 female patients and their ages ranged from 25 to 81 years.
Group 2 (the non-AKI group)
This group included 35 critically ill patients who did not develop AKI. It comprised 20 male and 15 female patients and their ages ranged from 25 to 77 years.
Group 3 (controls)
This group included 10 healthy individuals who were age and sex matched as much as possible with other groups, with ages ranging from 25 to 72 years.
Patients were selected from Internal Medicine, Neuropsychiatry, Cardiology, Chest and Anesthesia Intensive Care Units, Menoufia University Hospitals. They were selected during the period between June 2011 and June 2012.
Written consent was taken from the included individuals, and the study was approved by the local ethical committee of the hospital.
All patients were prospectively followed up from the time of ICU admission. Blood and urine samples were collected simultaneously at predetermined time points: at the time of ICU admission, 6 h after arriving, 12 h after arriving, and daily thereafter for a minimum of the next 2 days and a maximum of 5 days.
AKI was diagnosed by an increase in serum creatinine by 0.3 mg/dl or more over a period of 48 h or less  .
All patients and controls were subjected to:
- Full history taking.
- General examination with determination of BMI. BMI = weight in kilograms × (height in centimeters) 2 .
- Laboratory investigations including assessment of serum urea, serum creatinine, and urinary KIM-1 levels.
All acute critically ill patients were eligible for inclusion in the study.
- Pre-existing renal impairment.
- Peripheral vascular disease.
- Use of nephrotoxic drugs before or during the study period.
| Materials and methods|| |
KIM-1 determination 
Measurements of urinary KIM-1 levels were taken by Quantikine Human (R&D Systems, Inc., 614 McKinley Place, NE Minneapolis, MN 55413 USA) TIM-1 Immunoassay (USA), which is a radioimmunoassay technique.
Principle of the assay
This assay uses the quantitative sandwich enzyme immunoassay technique. A monoclonal antibody specific for T cell Immunoglobulin-Mucin (TIM-1) is precoated onto a microplate. Standards and samples are pipetted into the wells and any TIM-1 present is bound by the immobilized antibody.
After washing away any unbound substances, an enzyme-linked polyclonal antibody specific for TIM-1 is added to the wells. Following a wash to remove any unbound antibody-enzyme reagent, a substrate solution is added to the wells and color develops in proportion to the amount of TIM-1 bound in the initial step. The color development is stopped and the intensity of the color is measured.
TIM-1 microplate (Part 893803): a 96-well polystyrene microplate (12 strips of eight wells) coated with a mouse monoclonal antibody against TIM-1.
TIM-1 conjugate (Part 893804): 21.5 ml of a polyclonal antibody against TIM-1 conjugated to horseradish peroxidase with preservatives.
TIM-1 standard (Part 893805): 100 ng of recombinant human TIM-1 in a buffered protein base with preservatives, which is lyophilized.
Assay diluent RD1-82 (Part 895375): 11 ml of a buffered protein base with preservatives.
Calibrator diluent RD6Q (Part 895128): 21 ml of animal serum with preservatives.
Wash buffer concentrate (Part 895003): 21 ml of a 25-fold concentrated solution of buffered surfactant with preservatives.
Color reagent A (Part 895000): 12.5 ml of stabilized hydrogen peroxide.
Color reagent B (Part 895001): 12.5 ml of stabilized chromogen (tetramethylbenzidine).
Stop solution (Part 895032): 6 ml of 2 N sulfuric acid.
Plate covers: four adhesive strips.
Sample collection and storage
Urine was collected aseptically (mid-stream) and voided directly into a sterile container.
The sample was centrifuged to remove particulate matter (stored −20°C). Repeated freeze-thaw cycles were avoided [Figure 1].
- All kit components and samples were brought to room temperature (18-25°C) before use.
- The standard was reconstituted with 1.0 ml of standard diluent, kept for 10 min at room temperature, and shocked gently (not to foam). The concentration of the standard in the stock solution was 50 ng/ml. Seven points of diluted standard were set up, such as 50, 25, 12.5, 6.25, 3.12, 1.56, 0.78 ng/ml, and the last EP tubes being blanks with 0 ng/ml [Figure 1].
- Assay diluent A and assay diluent B: Assay diluent A concentrate of 6 ml was diluted with 6 ml of distilled water to prepare 12 ml of assay diluent A. Assay diluent B was prepared in the same manner.
- Detection reagent A and detection reagent B: Detection reagents A and B were briefly spinned before use. They were then diluted (1 : 100) to the working concentration with working assay diluents A and B, respectively.
- Wash solution: Wash solution concentrate of 20 ml was diluted with 580 ml of distilled water to prepare 600 ml of wash solution.
- TMB substrate: The required dosage of the solution was aspirated with sterilized tips. The residual solution was not dumped into the vial again.
- Wells for diluted standard, blank, and sample were determined. Seven wells for standard and one well for the blank were prepared. A volume of 100 ml of each of standard dilutions, blank, and samples was added to the appropriate wells, covered with plate sealers, and incubated for 2 h at 37°C.
- The liquid in each well was removed (not washed).
- A volume of 100 ml of detection reagent A working solution was added to each well and incubated for 1 h at 37°C after covering it with the plate sealer.
- The solution was aspirated. Wash solution of 400 ml was added to each well using a multichannel pipette and left for 1-2 min. The remaining liquid was removed completely from all wells by snapping the plate onto absorbent paper. This was repeated three times. After the last wash, the remaining wash buffer was removed by aspiration. The plate was invented and plotted against absorbent paper.
- A volume of 100 ml of detection reagent B working solution was added to each well and incubated for 30 min at 37°C after covering it with the plate sealer.
- The aspiration/wash process was repeated five times as conducted in step 4.
- A volume of 90 ml of substrate solution was added to each well, covered with a new plate sealer, incubated for 15-25 min at 37°C, and protected from light. The liquid turned blue by the addition of the substrate solution.
- A volume of 50 ml of stop solution was added to each well. The liquid turned yellow by the addition of stop solution. The liquid was mixed by tapping the side of the plate. Thorough mixing was ensured by tapping the side of the plate.
- The remaining drops of water were removed. No bubbles were present on the surface of the liquid. Then the microplate reader was run and measurement was taken at 450 nm immediately.
The recovery of TIM-1 spiked to levels throughout the range of the assay was evaluated.
Sample: urine (n = 20), average: 104%, recovery range: 94-112%.
Serum creatinine determination 
Serum creatinine concentrations were measured by means of the fixed rate kinetic method using diamond diagnostic international serum creatinine kits (UK).
| Results|| |
The mean age of the AKI group was 55.07 ± 11.33 years, whereas it was 55.11 ± 10.29 years for the non-AKI group, denoting a nonsignificant difference.
The mean BMI index in the AKI group was 29.78 ± 4.79 kg/cm 2 , whereas it was 28.69 ± 4.21 kg/cm 2 for the non-AKI group, denoting no significant difference.
Sex distribution percentage in the AKI group was 57% for male patients and 43% for female patients. It was also the same percentage in the non-AKI group.
Percentage of diabetic patients in the AKI group was 68%, whereas it was 29% in the non-AKI group, denoting a highly significant increase in the AKI group with respect to diabetes mellitus.
Percentage of hypertensive patients in the AKI group was 41%, whereas it was 31% in the non-AKI group, denoting no significant difference between the two groups with respect to hypertension [Table 1].
|Table 1: Comparison between AKI and non-AKI groups with respect to clinical and demographic characters|
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The mean value of the baseline KIM-1 level was 0.84 ± 0.29 ng/ml in the AKI group, whereas it was 0.85 ± 0.34 ng/ml in the non-AKI group. There was no significant difference between AKI and non-AKI groups with respect to baseline level of KIM-1.
The mean value of KIM-1 level after 6 h in the AKI group was 4.8 ± 1.55 ng/ml, whereas it was 0.93 ± 0.43 ng/ml in the non-AKI group. The mean value of KIM-1 level after 12 h in the AKI group was 5.67 ± 1.53 ng/ml, whereas it was 0.87 ± 0.35 ng/ml in the non-AKI group. There was significant increase in KIM-1 levels after 6 and 12 h in the AKI group.
The mean value of baseline serum creatinine in the AKI group was 0.81 ± 0.11 mg/dl, whereas it was 0.78 ± 0.9 mg/dl in the non-AKI group. There was no significant difference with respect to baseline serum creatinine between the AKI and non-AKI groups.
The mean value of serum creatinine measured after 12 h in the AKI group was 0.84 ± 0.12 mg/dl, whereas it was 0.79 ± 0.09 mg/dl in the non-AKI group. There was no significant difference with respect to serum creatinine after 12 h between the AKI and non-AKI groups.
The mean value of serum creatinine after 48 h in the AKI group was 1.48 ± 0.58 mg/dl, whereas it was 0.97 ± 0.09 mg/dl in the non-AKI group. There was no significant difference with respect to serum creatinine after 48 h between the AKI and non-AKI groups.
The mean value of the peak level of serum creatinine reached within 5 days of hospitalization in the AKI group was 7.5 ± 2.38 mg/dl, whereas it was 0.82 ± 0.1 mg/dl in the non-AKI group. The difference between the two groups was highly significant [Table 2].
|Table 2: Comparison between AKI and non-AKI groups with respect to KIM-1 levels and serum creatinine levels at different time points|
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In the AKI group, the mean level of KIM-1 during the patients' duration of stay in the ICU was 8.05 ± 3.33 ng/ml; development of sepsis was seen in 27% of patients, and hospital mortality was seen in 23%. In contrast, in the non-AKI group the mean level of KIM-1 during the patients' stay in the ICU was 4.06 ± 1.57 ng/ml; development of sepsis was seen in 6% of patients, and in-hospital mortality was seen in 6% [Table 3].
|Table 3: Comparison between AKI and non-AKI patients with respect to days in the ICU, sepsis, and in-hospital mortality|
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The mean level of KIM-1 after 6 h in the AKI group in patients who developed sepsis was 5.59 ± 1.78 ng/ml, whereas in patients who did not develop sepsis it was 4.51 ± 1.37 ng/ml. The mean level of KIM-1 after 12 h in the AKI group in patients who developed sepsis was 6.56 ± 1.74 ng/ml, whereas in those who did not develop sepsis it was 5.33 ± 1.32 ng/ml.
The mean level of KIM-1 after 6 h in the AKI group in patients with positive hospital mortality was 5.65 ± 1.67 ng/ml, whereas in patients with negative hospital mortality it was 4.56 ± 1.44 ng/ml. The mean level of KIM-1 after 12 h in the AKI group in patients with positive hospital mortality was 6.48 ± 1.81 ng/ml, whereas in patients with negative hospital mortality it was 5.43 ± 1.38 ng/ml [Table 4].
|Table 4: Association between KIM-1 levels at 6 and 12 h and the presence or absence of sepsis and in-hospital mortality in the AKI group (N = 44)|
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With regard to KIM-1 levels after 6 h, sensitivity was 100% and specificity was 97.1%. With regard to KIM-1 levels after 12 h, both sensitivity and specificity were 100%.
With regard to serum creatinine after 12 h, sensitivity was 86% and specificity was 42.9%. With regard to serum creatinine after 48 h, both sensitivity and specificity were 100% [Table 5].
|Table 5: Cutoff points, sensitivity, specificity, and predictive values of KIM-1 and serum creatinine for the detection of AKI in the studied critically ill patients (N = 44)|
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| Discussion|| |
Human KIM-1 is a type 1 transmembrane protein that is not detectable in normal kidney tissue or urine but is expressed at very high levels in dedifferentiated proximal tubule epithelial cells in human and rodent kidneys after ischemic or toxic injury and in renal cell carcinoma  . High urinary KIM-1 expression was also associated with adverse clinical outcomes in patients with AKI  .
Our study proved that KIM-1 can detect AKI as early as 6 h after its occurrence. This may be considered an addition to studies that have concluded that KIM-1 can be expressed in urine 12 h after initial renal ischaemic insult before regeneration of epithelium and that it persists over time. A sensitive urine test for proximal tubule injury will be useful for the evaluation of nephrotoxicity of pharmaceutical agents  .
Our study proved that diabetes mellitus is a risk factor for development of AKI in critically ill patients. This is consistent with the results of Leblanc et al.  who concluded that diabetes is a generally recognized risk factor for AKI in several settings. Hyperglycemia and insulin resistance are also common in critically ill patients, even in those without diabetes  , and are associated with increased morbidity and mortality.
Observational trials  , after correction for diabetes and other known risk factors, have shown an association between preoperative or intraoperative hyperglycemia and postoperative AKI after cardiac surgery  , between hyperglycemia at cardiac catheterization and contrast nephropathy,  and between hyperglycemia during total parenteral nutrition and the development of AKI  . Whether the degree of hyperglycemia simply reflects the severity of illness or actually contributes to adverse renal outcome can be demonstrated only by a randomized trial comparing correction or tolerance of elevated blood glucose levels.
Our study proved that hypertension is not a risk factor for the development of AKI. This was concordant to some extent with the results of Santhi et al.  who proved that mean arterial pressure in the critically ill is often tolerated up to a value of 135 mmHg for some hours. However, in some disorders (e.g. dissecting aortic aneurysm, cardiac failure, angina, acute myocardial infarction, pre-eclampsia, or eclampsia and following cardiac, vascular, or cerebral surgery) a mean arterial blood pressure of 90 mmHg or greater should be treated urgently.
In contrast, Szczech et al.  said that in cases of acute severe hypertension, AKI is a frequent form of acute target organ dysfunction, particularly in those with baseline chronic kidney disease. Any degree of AKI is associated with a greater risk for morbidity and mortality.
Our study proved that higher levels of KIM-1 are associated with higher incidence of morbidity and mortality, as established by Liangos et al.  , who studied the relationship between adverse events and the levels of KIM-1 and N-acetyl-μ glucosaminidase (NAG) activity in urine in 201 hospitalized patients with AKI. They divided patients into four quartiles depending on the levels of KIM-1 and NAG. They found that patients in the higher quartiles of KIM-1 and NAG levels were at high risk of undergoing dialysis or have higher mortality compared with patients in the lower quartiles on univariate analysis. For the composite outcome of dialysis or death.
In our study, we proved that assessment of urinary KIM-1 levels serves as a noninvasive, rapid, sensitive, reproducible, and potentially high-throughput method to detect early kidney injury in critically ill patients.
The FDA and EMEA have included KIM-1 in the small list of kidney injury biomarkers that they will now consider in the evaluation of kidney damage as part of their respective drug review processes of new drugs  .
| Conclusion|| |
Our study stated that KIM-1 is a reliable early marker for AKI with excellent sensitivity and specificity, especially in critically ill patients, as compared with traditional markers. KIM-1 can detect AKI as early as 6 h from its occurrence and before elevation of conventional markers (e.g. serum creatinine). KIM-1 was found to be a reliable indicator of morbidity and mortality in critically ill patients.
| Acknowledgements|| |
The authors thank all the workers and the participants who generously agreed to participate in the study.
Conflicts of interest
There are no conflicts of interest.
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[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]