Original Articles

By Mr. Rinu John Mathew , Mr. Nikhil Raj , Mr. Vivek Raghavan , Dr. Ganesh Kamath , Dr. Asha Kamath , Dr. Saleena U Velladath , Dr. K Nalini , Dr. K Gopalakrishna
Corresponding Author Dr. Saleena U Velladath
Medical Lab Technology, School of Allied Health Sciences, Manipal University, Associate Professor, Dept. of MLT, MCOAHS, Manipal University - India 576104
Submitting Author Dr. Saleena U Velladath
Other Authors Mr. Rinu John Mathew
Medical Lab Technology, Sikkim Manipal University, - India

Mr. Nikhil Raj
Al-Sabah Hospital, Kuwait City, - India

Mr. Vivek Raghavan
Medical Lab Technology, School of Allied Health Sciences, Manipal University, - India

Dr. Ganesh Kamath
Cardiothoracic Surgery, - India

Dr. Asha Kamath
KMC Manipal, - India

Dr. K Nalini
KMC Manipal, - India

Dr. K Gopalakrishna
KMC Manipal, - India


Acute Kidney Injury, Cardiac Surgery, Estimated Glomerular Filtration Rate, AKIN criteria, RIFLE criteria

John Mathew R, Raj N, Raghavan V, Kamath G, Kamath A, Velladath SU, et al. Acute kidney injury in post cardiac surgery - An evaluation with eGFR (Estimated glomerular filtration rate) and akin Criteria. WebmedCentral CLINICAL BIOCHEMISTRY 2014;5(11):WMC004745
doi: 10.9754/journal.wmc.2014.004745

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Submitted on: 04 Nov 2014 05:59:52 PM GMT
Published on: 06 Nov 2014 12:29:45 PM GMT


Acute Kidney Injury (AKI) is one of the major complications of cardiac surgery affecting 17% to 45% of the cardiac surgical patients and is associated with high morbidity and mortality. Prevention and management of AKI in post cardiac surgery is still a clinical problem as the lack of early markers. We designed this study as a single centered retrospective cohort study to find out the proportion of the kidney injury in patients underwent cardiac surgery and to evaluate the efficiency of eGFR and AKIN criteria for the early prediction of AKI. From the medical records the retrospective data of consecutive patients (January 2008 to November 2013), were collected and analyzed. Diagnosis of kidney injury was confirmed by a serum creatinine level > 1.4mg/dL. Out of 301 patients (aged between 18 to 75 years) studied 26.91% were diagnosed with AKI. AKIN criteria identified 31.22% with AKI and based on eGFR it was 29.25%. Our findings say that, both AKIN and eGFR estimations may be useful for earlier detection of AKI than serum creatinine. The high incidence of AKI associated with cardiac surgery should prompt the inclusion of these parameters in the prediction of kidney damage to identify patients at increased risk for the timely management and patient care.


Acute kidney injury (AKI), is a rapid loss of kidney function[1]. AKI occurs in as many as 45% of patients after cardiac surgery and requires dialysis in 1% of cases. It is associated with an increased hazard of morbidity and mortality, leads patients to a long hospitalization, requires additional treatments, and increases the hospital costs[2]. It is indicated by a progressive worsening course, being the result of the interplay of different pathophysiologic mechanisms, with patient- associated factors and cardiopulmonary bypass as major reasons. It may directed to a number of complications, including metabolic acidosis, high potassium levels, uremia, changes in body fluid balance, and effects to other organ systems[3,4].

AKI is diagnosed on the basis of characteristic laboratory findings, such as raised serum creatinine and blood urea nitrogen and, or inefficiency of the kidneys to produce sufficient amounts of urine. Several novel biomarkers have emerged during the last few years, demonstrating reasonable sensitivity and specificity for AKI prediction and protection[5]. The development and execution of potentially protective therapies for AKI remains essential, especially for the relevant impact of AKI on early and late survival[2].

Reports from various groups have described the incidence and prognostic importance of cardiac surgery-associated AKI for clinical outcomes in different patient settings, and these have been placed both in the context of the specific operation performed and the type of practice. It is at present realized that the overall incidence of AKI after adult cardiac surgery is about 5% to 10% and is highly dependent on pre-existing renal function and the complexity of the proposed surgery[6].

Acute kidney injury network (AKIN) introduced a specific criteria for the diagnosis of AKI[7]. This criteria depends on the reduction of kidney function which is dependent on rise in serum creatinine, ie, absolute increase in serum creatinine of ≥ 0.3 mg/dl or ≥ 26.4 µmol/L and reduction in urine output, defined as < 0.5 ml/kg/hr for more than 6 hours.

A recent report from the Laboratory Working Group of the National Kidney Disease Education Program, recommends that serum creatinine alone should not be applied to assess the GFR or to observe the presence of kidney disease.  Because serum creatinine is affected by the GFR and by factors independent of the GFR, including age, sex, race, body size, diet, certain drugs, and laboratory analytical methods[8]. Rather, the Working Group suggests implementing the estimated GFR calculated using the different formulas.

In the absence of suitable baseline data, the ADQI recommends an estimation of serum creatinine levels based on back calculation from the modification of diet in renal disease (MDRD) formula assuming a normal GFR of approximately 75- 100 ml/min/1.73 m2[9]. A commonly used surrogate marker for estimate of creatinine clearance is the Cockcroft-Gault formula, which in turn estimates GFR in ml/min. One of the main features of the Cockcroft and Gault equation is that it shows effect of age on the estimation of CCr[10]. These factors entail the need to evaluate the diagnostic efficiency of eGFR and AKIN criteria for predicting AKI and compare their fulfillment in detecting kidney injury associated with cardiac surgery[11].

The purpose of this study was to find out the proportion of kidney injury in post cardiac surgery patients attending a tertiary care hospital in south India (Kasturba Hospital, Manipal) and to evaluate and compare the eGFR and AKIN criteria for the diagnosis of AKI in patients underwent cardiac surgery.


This study was designed as a retrospective cohort study. The study group comprised of patients who underwent cardiac surgery in Kasturba Medical college, Manipal. Ethical clearance was obtained from institutional ethic committee (IEC 429/2012). Anticipating a 40% of post cardiac surgery cases (based on previous records) to develop AKI for a 15% relative precision and for comparison of the predictive value of the eGFR with that of AKIN, at an alpha value of 0.05, a sample size of 260 post cardiac surgery cases studied at 95% confidence level (80% power to detect a difference in AUC–ROC values of 0.1 performance units). Expecting an exclusion of around 60 patients a total of 320 patients were included in the study. Finally 301 patients were participated in the study after excluding 19 patients as per the eligibility criteria.

Evaluation of the proportion of kidney injury in post cardiac surgery patients

From the medical records the retrospective data of consecutive patients underwent cardiac surgery from January 2008 to November 2012 were collected. The data on age, sex, height, weight, the presence or absence of arterial hypertension, duration of hospital stay, type of surgery, other co-morbidities, and the data on all biochemical parameters of all the enrolled patients were collected and analyzed. Diagnosis of kidney injury was confirmed by a serum creatinine level > 1.4mg/dL.

Evaluation of eGFR and AKIN criteria for the diagnosis of AKI

GFR was estimated using the Cockcroft Gault formula[12], ie,

eGFR   =  (140-age) x Weight in Kg x (0.85 if female) / 72 x SCr.(mg/dl).

The patients were grouped as AKI when the difference in eGFR from the baseline (before Surgery) is > 25% and those with < 25% difference grouped under non-AKI. The selected patients were grouped using AKIN criteria[13] also. ie, Those patients with an increase in serum creatinine of  ≥0.3 mg/dl from baselinewere grouped under AKI and those with < 0.3mg/dl grouped under non-AKI group.

Statistical Analysis

Continuous variables were summarized as mean and standard deviation or standard error. Categorical variables were summarized as percentages. Association of eGFR and AKIN criteria for the diagnosis of AKI was studied by Mc Nemar test. The diagnostic efficiency of these parameters were assessed by ROC analysis and further calculations. The analysis was done using SPSS, version 16.


The present study included 320 patients who underwent cardiac surgery at KMC Hospital, Manipal. Acute kidney injury was confirmed by a serum creatinine level of > 1.4 mg/dl. According to Serum Creatinine levels, out of the total 301 subjects 81(26.91%) were diagnosed with acute kidney injury(Fig 1). Whereas based on AKIN criteria 94 (31.22%) were grouped into acute kidney Injury. When diagnosis of AKI was carried out based on eGFR the number of AKI cases were reduced to 70 (23.25%).

Table 1:  Patient characteristics (Check the attached illustrations)

Evaluation of eGFR and AKIN Criteria

When the Performance of AKIN criteria for the diagnosis of AKI was studied by ROC analysis, an AUC of 0.796( 95% CI: 0.740 – 0.852), with sensitivity of 78% and Specificity of 69% (Cut off value: 13.8% (percentage difference from baseline) were obtained(Fig 3). When the diagnostic efficiency of eGFR was studied by ROC analysis an AUC of  0.797( 95% CI: 0.741 – 0.853), with sensitivity of 77% and Specificity of 70% (Cut off value: 24.5% (percentage difference) were obtained(Fig 2).

Comparison of eGFR and AKIN criteria

When the diagnostic characteristics of eGFR and AKIN criteria were compared, the Mc Nemar test revealed a significant association. (P < 0.001). According to AKIN Classification, 92% of the AKI group patients were categorized as AKIN Stage-I and 8% patient as AKIN Stage-II. Based on RIFLE Classifcation, 94% the AKI group patients were grouped under Risk Category and 6% patients in Injury Category

Comparison of biochemical parameters before and after cardiac surgery

Several parameters studied before and after cardiac surgery were compared using student  t Test. Few biochemical parameters including Hb, Urea, Potassium and Creatinine showed a significant difference before and after cardiac surgery.

Table 2: Comparison of Biochemical parameters before and after cardiac surgery in AKI (Check the attached illustrations)


Cardiopulmonary bypass (CPB) surgery is the most frequent major surgical procedure performed in hospitals worldwide, with well over a million operations undertaken each year in adults alone. AKI is common in cardiac surgery patients, particularly those with elevated preoperative serum creatinine and is associated with significant morbidity and death rate[14].

We conducted a retrospective study to compare and clarify the diagnostic importance of the eGFR estimation and AKIN classifications for AKI after cardiac surgery. The proportion of AKI in post cardiac surgery based on AKIN criteria was slightly more than that based on eGFR but ROC analysis shown a similar diagnostic value. There was large agreement between classifications according to patients graded as not having AKI.

Our study compared the sensitivity and specificity of the AKIN and eGFR classifications in assessing the presence of AKI. The RIFLE criteria have been assessed in prior studies in an effort to validate its role in different clinical contexts such as intensive care units (ICU), non-ICU settings, and cardiac patients[15]. With the development of the revised AKI classification with the AKIN criteria, some studies have tried to compare the performance of the RIFLE and AKIN criteria in determining in-hospital mortality[16]. Findings of Study conducted by Joannidis and coworkers were significant for increased observed mortality among patients who had AKI compared with expected mortality based on the severity of their illness, with higher mortality at each stage of AKI[15].

Haase and colleagues led a small prospective study to compare the RIFLE and AKIN criteria in their performance for detection of AKI and prediction of in-hospital mortality. In their analysis conducted on a sample size of 282, patients who underwent cardiac surgery, a similar percentage of patients developed AKI by both the RIFLE and AKIN criteria assessment[17].

Furthermore, both sets of criteria demonstrated similar performance in predicting in-hospital mortality, with sCr being the strongest predictor and urinary output the weakest predictor of in-hospital mortality. Our study extends findings of prior studies by supporting that both RIFLE criteria and AKIN criteria are equivalent predictors of AKI. The advantages of the AKIN criteria are that it does not require a baseline creatinine, as two sCr values within 48 hours would suffice to detect a change in renal function and development of AKI; it does not require measurement of urinary output, as those measurements are clinically known to be inaccurate; and it simplifies the classification of AKI with three stages.

Changes in eGFR are central to clinical decision making in daily practice. For clinical decision making, it is important to consider the clinical context when interpreting changes in eGFR. As such, for routine clinical decision making, we suggest that it would be reasonable for clinicians to interpret a change in eGFR as a reflection of a change in measured GFR and act accordingly. However, if clinical circumstances suggest a change in non-GFR determinants of serum creatinine, the change in eGFR could reflect the change in non-GFR determinants of serum creatinine, rather than a change in measured GFR. In all patients, clinicians should consider measuring GFR as a mandatory test that would improve clinical decision making[18].

Our analysis shows few limitations. We did not use urine output to assist in classifying renal function of patients. Thereason is because accurate documentation of preoperative and postoperative urine output has not been demonstrated.  As we did not want to compromise the accuracy of our analysis, we have only used changes in sCr to stage patients using both the RIFLE criteria and the AKIN criteria. Additionally, the AKIN criteria require changes in serum creatinine or urine output, but not both, as do the previous RIFLE criteria. Furthermore, previous studies (Barrantes and colleagues and Mehta) validated the diagnostic ability of sCr over urine output, demonstrating the predictability of AKI on mortality using only sCr (AKIN definition).

In conclusion, the AKIN criteria and the eGFR criteria were developed in attempt to improve detection of and care for patients who experienced an acute decrease in renal function after cardiac surgery. Based on our analysis, both AKIN and eGFR estimations can be used as an early predictors of AKI. The high incidence of AKI associated with cardiac surgery should prompt the use of either AKIN criteria or eGFR estimation in the early postoperative period to identify patients at increased risk and to stimulate institutional measures that target AKI as a quality improvement initiative.

The biomarkers study can give more accurate result for future studies[18]. According to current scenario, study enlightens the need for eGFR and AKIN classification together with routine estimation as it does not require any additional cost but it gives us vital information for the well being of patient.


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Source(s) of Funding

Manipal University

Competing Interests


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