Kidneys are instrumental in eliminating toxins and waste substances, including uric acid, creatinine, and urea, extracellular fluid volume regulation, electrolyte concentrations, serum osmolality, and hormone production. This paper provides a comprehensive analysis of the chemical procedures used to diagnose kidney disorders and advancements in kidney testing methodologies. I will also present my thoughts regarding the elements a novel examination may target.
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Chemical Methods Used to Diagnose Kidney Disease
Glomerular Filtration Rate (GFR)
The GFR is the most effective glomerular function indicator; it relates to the millilitres per minute filtration rate of compounds contained in plasma via the glomerulus.
Currently, there is no endogenous marker with the recommended features, and therefore, exogenous GFR markers are commonly utilized for assessing GFR. GFR analysis using a polysaccharide identified as inulin is regarded as the reference procedure for GFR estimation. Other common exogenous markers used for GFR assessment include radioisotopes such as 99 Tc-DTPA and 51 Cr-EDTA.
Creatinine is the most conventional endogenous marker used to assess glomerular function. It incorporates urine collection over a twenty-four-hour period, or ideally over a precisely scheduled time (five to eight hours) and, according to Chwala and Ronco (2016), twenty-four-hour collections are notably capricious or unreliable. Incomplete or inappropriate urine sampling is among the primary factors impacting this test’s accuracy; therefore, a scheduled collection is crucial. Serum creatinine is an advanced renal impairment indicator – according to Chwala and Ronco (2016), renal function is reduced by fifty percent before a serum creatinine surge is observed. GFR is categorized in various phases depending on one’s kidney disorder. Since eGFR uses serum creatinine, the effects of issues related to serum creatinine computations are typical; this, therefore, demands corrections for factors, including age, gender, and race.
Blood Urea Nitrogen (BUN)
BUN relates to a nitrogen-comprising substance produced within the liver as a urea cycle and protein metabolism’s end product. Approximately eighty-five percent of urea is excreted by kidneys. Serum creatinine represents a more effective renal function evaluation test compared to urea; nonetheless, urea levels are usually elevated earlier in kidney disorders. The proportion of BUN-to-creatinine (BUN: creatinine) may be instrumental in differentiating prerenal conditions from renal triggers, particularly if BUN rates are high. Cystatin C
This is a protein with low-molecular-weight that works by inhibiting protease secreted by the body’s nucleated cells. This compound is produced continually and is freely cleared by the kidney. This component is usually measured in urine and serum, and it is not impacted by diet, muscle bulk, or age. It is also been included in the eGFR equations, including the creatinine-cystatin KDIGO CKD-EPI equation.
Proteinuria and Albuminuria
Albuminuria relates to the unusual albumin present in the urine. It is utilized as a marker for detecting incipient nephropathy in individuals diagnosed with diabetes. Urine protein measurement can be performed using random urine protein: creatinine proportion or a twenty-four-hour urine collection.
Tubular Function Tests
Renal tubules are instrumental in water and electrolyte reabsorption and in sustaining the acid-base balance. Electrolytes, including glucose, phosphate, magnesium, chloride, potassium, and sodium, can be computed in urine. Urine osmolality measurements facilitate the evaluation of tubules’ concentrating capacity.
Urine Analysis Urine analysis incorporates urine characteristics’ assessment to help in disease diagnosis. It involves microscopic and chemical examination as well as physical observation. Physical inspection is concerned with analyzing clarity and color. It utilizes dry chemical procedures to determine the presence of leukocyte esterase, nitrite, urobilinogen, bilirubin, ketones, blood, glucose, and protein presence. Microscopic analysis entails a wet-prep urine evaluation to examine micro-organisms, casts, and crystals’ presence. The most appropriate specimen for this function test is freshly voided urine – midstream; this is because midstream urine’s contamination by compounds including epithelial cells as well as commensal bacteria is less likely.
Kidney Tubular Distress Assessment
Organ systems within the human body have developed the ability to expand their functioning in distressful conditions. The reserve capacity assessment represents an effective tool for uncovering subclinical disorders. Kidneys stress testing appears to provide significant cognizance of the absence or presence of kidney disorder (KD) and parenchymal loss ascribed to fibrosis and injury. The renal reserve capacity is ground on two primary features: tubular and glomerular (Figure 1). Figure 1: Renal reserve capacity testing.
Glomerular Reserve Testing (GRT)
GRT has been elucidated comprehensively; however, its use in daily clinical practice is limited. GFR, a test utilized as a kidney function surrogate, relies on diet, weight, sex, or age, and, therefore, it presents significant fluctuations among patients. The variation amid baseline and maximal GFR is regarded as the renal glomerular function reserve. It is directly linked with distress-correlated nephron recruitment and elevated renal flow of blood. Nonetheless, the deficiency of large cohort surveys crucial in delineating the renal glomerular function reserve’s populace variability serves as a significant shortcoming for this assessment.
Tubular Reserve Capacity
Tubular reserve capacity’s application in clinical practice bears significant potential. Tubular reserve (TR) may be examined by testing the kidney tubule’s secretion capacity, and it can be informative in various situations. The primary tool for assessing tubular function is to evaluate an exogenous or endogenous substance’s tubular secretion, including furosemide and creatinine. Acid or salt loading can be utilized to assess the tubule’s efficiency in eliminating acid or sodium.
Furosemide Stress Evaluation (FST)
FST is ground on furosemide’s pharmacokinetic attributes, and it aims to evaluate the renal tubule’s functional capacity. Furosemide generates minimal urine levels in CKD patients irrespective of its extended plasma half-life. This phenomenon is attributed to the renal blood flow decline and decreased tubular secretion. Urinary outpost is posited as a renal tubular function capacity surrogate marker; it could assist clinicians in distinguishing individuals with tubular injury and those at significant CKD or AKI progression risks.
Thoughts on What a Novel Test May Target
From the extensive research on kidney diseases and the relevant renal function tests, I believe a novel test for this condition should be capable of detecting early kidney damage signs and prognosis by measuring or computing even low protein marker levels in blood and urine samples. A novel test should consist of non-invasive markers and target a specific site and organ to facilitate the detection of early injury and differentiation amid extrarenal, prerenal, and intrarenal kidney injury causes. It should integrate the use of highly sensitive markers with minimal biological variability to better longitudinal changes evaluation.
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Chawla, L. S. and Ronco, C., “Renal Stress Testing in the Assessment of Kidney Disease,” Kidney International Reports, vol. 1, no. 1, 2016, pp. 57-63. Web.
Coca, A. et. al., “Role of the Furosemide Stress Test in Renal Injury Prognosis,” International Journal Molecular Science, vol. 21, no. 9, 2020, pp. 1–12. Web.
Rivero, J. et al., “Furosemide Stress Test and Interstitial Fibrosis in Kidney Biopsies in Chronic Kidney Disease,” BMC Nephrology, vol. 21, 2020, pp. 1-9. Web.
Ronco, C.and Chwala, L. S., “Glomerular and Tubular Kidney Stress Test: New Tools for a Deeper Evaluation of Kidney Function,” Nephron Clinical Practice, vol. 134, 2016, pp. 191-194. Web.
Rysz, J., “Novel Biomarkers in the Diagnosis of Chronic Kidney Disease and the Prediction of Its Outcome,” International Journal Molecular Sciences, vol. 18, no. 8, 2017, pp. 1-17. Web.