CARDIOVASCULAR JOURNAL OF AFRICA • Volume 34, No 5, November/December 2023 282 AFRICA The ROC curves for MHR were associated with postoperative AKI following isolated CABG (Fig. 1). The area under the curve for MHR was 0.851 (95% CI: 0.826– 0.876; p = 0.0001). Using a cut-off value of 0.0212, MHR predicted postoperative AKI with a sensitivity of 78.9% and a specificity of 78.4%. Discussion In this study, elevated pre-operative MHR was associated with early postoperative AKI after isolated CABG operation. To the best of our knowledge, this is one of the first studies to evaluate the relationship between MHR and AKI after CABG operation. One of the most important treatment modalities preferred for many patients with coronary artery disease is CABG, and patients undergoing this surgery are at risk of serious complications.17 One of these complications is AKI, with an incidence rate of 5–42%, and which is associated with higher patient morbidity and mortality rates, length of hospital stay and cost.18 AKI, which has been the subject of intense research in the last 20 years, is the sudden loss of kidney function characterised by an acute increase in sCr concentration.19 There are multiple diagnostic criteria for AKI developing after cardiac surgery. Although there are many new studies available for the diagnosis of advanced AKI, sCr and blood urea nitrogen (BUN) used together with urine output remain the cornerstone of diagnosis in clinical practice.20 In our study, we used sCr and BUN values for the diagnosis of AKI. While AKI causes an increase of 10–30% in hospital mortality rate, this increase reaches up to 40–60%when dialysis is required.21 Hobson et al. reported that 43% of their patients developed AKI during hospital follow up after cardiac surgery.22 For standardisation, patients operated on for only isolated CABG using standard CPB were enrolled in our study. Postoperative AKI and acute renal failure occurred in 16.9 and 4.3% of the patients, respectively, in parallel with the literature. The incidence of AKI following cardiac surgery depends on its definition. The risk, injury, failure, loss of kidney function, and end-stage kidney disease (RIFLE) classification, acute kidney injury network (AKIN) criteria and kidney disease improving global outcomes (KDIGO) stages, are all practical predictors of AKI after cardiac surgery.15 In our study, AKI was defined according to the KDIGO criteria. The pathophysiology of AKI developing after cardiac surgery is complex and multifactorial, including renal ischaemia– reperfusion injury, exogenous and endogenous toxins, radiocontrast agent use, neurohormonal activation, metabolic factors, hypoproteinaemia, inflammation and oxidative stress.23 Ischaemia–reperfusion is the most common cause of post-cardiac surgery AKI and is associated with the pathological features of acute tubular necrosis.24 In addition, there are studies stating that inflammation plays a key role in the initiation and progression of AKI that develops after cardiac surgery, while oxidative stress and haemolysis are pathways that complement inflammation.25 In general, it has been shown that direct or indirect suppression of the inflammatory response could significantly reduce the degree of kidney injury in an animal model, which manifested as a relative decrease in sCr levels and a reduction in tubular necrosis.26 Various risk models have been defined to predict CABGrelated mortality and morbidity, and many blood markers have been investigated in this regard.27 In recent years, novel structural biomarkers used in clinical practice as early and rapid indicators of AKI developing after cardiac surgery have facilitated evaluation of disease occurrence and progression.28 A number of urine and blood biomarkers, including neutrophil gelatinase-associated lipocalin (NGAL), interleukin-18, cystatin C and kidney injury molecule-1 (KIM-1) are elevated before sCr levels and facilitate the early diagnosis of AKI.29 Biomarkers such as urinary liver fatty acid binding protein (L-FABP), urinary NGAL, serum L-FABP, heart type FABP, KIM-1 and interleukin-18 have been found statistically significantly higher in patients who develop AKI after cardiac surgery.28 Novel biomarkers are required to replace current clinical risk classifications in order for clinicians to design new clinical trials to take appropriate preventative measures for AKI and evaluate clinical properties to determine effective treatments.29 In our study, we aimed to identify possible pre-operative blood biomarkers as candidates that would improve the prediction of AKI, alone or in combination with the existing clinical scoring tools, in patients undergoing isolated CABG with CPB. In recent studies, it has been shown that various inflammatory biomarkers, including WBC, leukocyte subtypes, platelet count, CRP level, NLR and PLR are important prognostic determinants in various cardiovascular diseases.7 Meta-analysis studies by Wu et al. reported that strong haematological inflammatory indicators such as haematocrit and red blood cell distribution width were associated with contrast-induced nephropathy.30 In another study, Parlar et al. reported that NLR values measured in the first four postoperative days of CABG were useful in predicting AKI during hospital stay.31 In our study, we found that CRP, ESR and MPV values, which are important inflammatory biomarkers, were significantly higher in patients who developed AKI both pre- and early postoperatively. Neutrophils, lymphocytes, monocytes and eosinophils, which are leukocyte subtypes, have separate roles in inflammation, host defence and tissue repair.32 Monocytes, which are innate and one of the basic components of the human immune system, are circulating leukocytes that play an important role in inflammation and tissue remodelling.25 Activated macrophages andmonocytes secrete various pro-inflammatory andpro-oxidant mediators, attaching to the inner surface of the arterial wall and initiating the atherosclerotic process.32 Monocyte counts have recently been suggested as a predictor of coronary events, and increased monocyte counts have been associated with adverse cardiovascular endpoints in coronary artery patients.9 In our study, similar to other studies, we found that pre-operative high monocyte count was an independent predictor of postoperative AKI development. HDL-C, a component of the lipid profile, can prevent free cholesterol and triglyceride accumulation in the vessels; it protects endothelial cells against the negative effects of LDL-C by preventing its oxidation.33 Studies have reported that HDL-C has pleiotropic protective functions including antiinfectious, antithrombotic, anti-inflammatory, antioxidant and immunomodulatory properties.14 In addition, HDL-C inhibits the endothelial expression of adhesion molecules and prevents the infiltration of monocyte cells into the arterial wall.27 The inverse relationship between HDL-C levels and cardiovascular disease risk has been well known for a long time.33 Many prospective studies from different racial and ethnic groups
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