Acute kidney injury (AKI) is not a rare complication during anti-TB treatment in some special population[7]. Renal function impairment failure to recover within 7 days will progress to acute kidney disease (AKD)[14]. Therefore, the prediction model to Identify the risk for AKI is of great significance.
Chronic diseases such as diabetes, hypertension, viral hepatitis are common causes of kidney function damage[15]. More importantly, diabetes mellitus is a major risk factor for the infection of latent tuberculosis[16]. To avoid mixed effects, 184 PTB patients with the underlying disease were not included in our study. After comparing the clinical data of 371 PTB patients, 7 factors (Microalbuminuria, Hematuria, CYS-C, Albumin, eGFR, BMI and CA-125) are acquired to develop the predictive model. The independence of factors is verified before the logistic analysis. According to the binary logistic regression, 4 parameters (Microalbuminuria, Hematuria, CYS-C, CA-125) were high-risk factors for AKI in PTB patients during anti-tuberculosis treatments, and ALB is a protective parameter against AKI development.
Urine microalbumin is considered an important marker of preclinical nephropathy[17]. Patients with increased urine microalbumin have a higher risk of long-term eGFR reduction[18]. In this study, approximately 50% of PTB patients with AKI have to find haematuria before anti-tuberculosis treatment. According to the AUA guideline, haematuria is generally secondary to the potential underlying risk of the clinical syndrome, including tumor, urolithiasis, and nephropathy[19]. Compared with serum creatinine or eGFR (creatinine-based glomerular filtration rate estimates), cysteine protease inhibitor C (CYS-C) has a higher sensitivity to predict early renal injury. CYS-C is useful to differentiate types of AKI and is strong predictors for acute renal injury[20]. As an endogenous inhibitor of cysteine proteinases, CYS-C has the characteristics of non-adhesion to plasma proteins and low molecular weight and is freely filtered by the glomeruli. Cysteine protease inhibitors belong to a group of proteins with characteristic tertiary structure and the ability to bind closely but reversibly to the active site of cysteine protease (cathepsin) and thereby inhibit its activity. Cysteine protease inhibitor C plays an important role in controlling protease activity in immune system regulation, antiviral, and antimicrobial activities[21]. Eventually, CYS is partially reabsorbed and decomposed in the proximal tubular cells[22]. While studies have confirmed that the value of CA-125 is related to the severity of pulmonary tuberculosis[23]. Serum CA-125 is beneficial in the differentiation between active and inactive pulmonary tuberculosis[24]. However, the mechanism of CA-125 elevation after TB infection is still unclear. Tuberculosis can lead to malnutrition and poor nutritional status may predispose to tuberculosis. ALB(albumin) and BMI(body mass index) are the direct indicators to reflect the nutritional status of patients. Cell-mediated immunity is the key host defense against Mycobacterium tuberculosis. Malnutrition is an important risk factor of immune system abnormality in tuberculosis patients[25]. Both innate immune and adaptive immune play specific roles in the development of AKI[26]. In consequence, severely malnourished PTB patients have a higher risk of developing AKI.
Nomograms are introduced to the medical field by J.L. Henderson in 1928. Nomograms can be used to predict the probability of the outcome of the regression model[27]. As shown in the nomogram plot (Fig. 3), PTB patients with microalbuminuria, hematuria, a higher value of CYS-C, and CA-125 are more likely to develop AKI during anti-tuberculosis treatment. Nevertheless, PTB patients who had higher ALB are at a lower risk in AKI development. By summing the total score and locating the score on the total point scale, the development of AKI can be predicted for PTB patients before anti-tuberculosis treatment. PTB patients with a total score of 132 have 50% risk of developing AKI after the start of anti-tuberculosis. The prediction model discrimination and calibration are evaluated by ROC Curve, and Hosmer-Lemeshow analysis. According to the above-mentioned analysis, we believe that the initial treatment of PTB patients with malnutrition, microalbuminuria, hematuria, CA-125 positive, and high value of Cystatin-C should not be received anti-tuberculosis immediately. If patients with pulmonary tuberculosis fail to improve their nutritional status and take measures to protect kidney function in advance, they have a greater risk of AKI after the start of anti-tuberculosis.
After comparing the immunological indexes, we confirmed that PTB patients with AKI have high numbers of CD3+ T cells, and the value of CD4+T cell/CD8+ T cell, IgG and IgA in AKI Group are significantly higher than those in the control Group. The natural infection process of Mycobacterium tuberculosis is complex. Firstly, Mycobacterium tuberculosis invades alveolar macrophages, replicates in macrophages, and spreads to macrophages, myeloid dendritic cells, and neutrophils recruited from the surrounding areas, and finally triggers adaptive immunity[28]. The tubercle bacillus produces excessive tumor necrosis factor after infection, and produces excessive mitochondrial reactive oxygen species (ROS) through the mitochondrial-endoplasmic reticulum circuit, triggering the programmed necrosis of macrophages[29]. Acute kidney injury is associated with increased oxidative damage, superoxide radical anion, peroxide, and hydroxyl radical can oxidize biomolecules and membrane, affect organelle function, and eventually induce renal tubular cell injury[30]. Active TB is frequently associated with a substantial increase in serum IgA levels. Besides, the ratio of T cells is positively correlated with serum IgA level. The deposition of immune complexes in the kidney leads to renal dysfunction[31]. Confusingly, we do not yet know the exact cause of AKI in PTB patients, whether the deposition of immune complexes produced by tuberculosis infection damages the glomerulus, or whether anti-tuberculosis drugs such as rifampicin can damage the tubular or interstitial substance AKI, or whether both play an important role[7]. At present we can make it clear that some PTB patients have a higher risk of AKI during anti-tuberculosis treatment, and nephrotoxic drugs and special tests such as coronary angiography need to avoid[32].
Limitations
The proportion of AK in PTB patients in this study is higher than that reported in relevant clinical studies. The individuals included in our study are hospitalized patients with more severe pulmonary lesions, which may lead to statistical bias. This study failed to collect the long-term outcomes of AKI patients, and the relevant factors affecting the long-term outcomes of patients will be statistically verified in the future. The mechanism of AKI in PTB patients needs to be further studied to provide a theoretical basis for clinical prevention and treatment.