Renal Function Biomarker Research: Integrated Evaluation of Filtration Function, Tubular Injury, and Urinary Indicators

Renal function biomarker research is used to evaluate renal status from multiple dimensions, including glomerular filtration, tubular injury, filtration barrier integrity, and renal endocrine regulation. Traditional indicators such as serum creatinine, blood urea nitrogen, and urinary protein are suitable for routine renal function screening, but their ability to distinguish early injury or injury sites is limited. Biomarkers such as Cystatin C, KIM-1, NGAL, β2-microglobulin, and Nephrin can further supplement information on early injury, tubular responses, and glomerular barrier changes, shifting renal function assessment from a single endpoint to multi-biomarker integrated analysis.

Keywords: renal function biomarkers; creatinine; Cystatin C; KIM-1; NGAL; β2-microglobulin; urinary protein; tubular injury

 

1 Research Logic of Renal Function Biomarkers

1.1 Why a Single Indicator Is Not Enough

Renal function is not equivalent to serum creatinine alone. The kidney performs filtration, reabsorption, excretion, endocrine regulation, and barrier maintenance simultaneously, and different biomarkers reflect different pathological processes. Relying on a single indicator may miss early injury, localized tubular damage, or filtration barrier abnormalities.

(1) Filtration function indicators

Serum creatinine and Cystatin C are mainly used to reflect glomerular filtration function. Creatinine testing is mature and widely used, but it is affected by muscle mass, age, sex, and dietary status. Cystatin C is less affected by muscle mass and is more suitable as a supplementary indicator for early decline in filtration function.

(2) Tubular injury indicators

KIM-1 and NGAL are commonly used to evaluate tubular injury, especially in studies of acute kidney injury, drug-induced nephrotoxicity, ischemia-reperfusion injury, and tubular stress responses. Compared with creatinine, these indicators are more closely related to injury responses rather than simple filtration function outcomes.

(3) Urinary protein indicators

Urinary protein, β2-microglobulin, and Nephrin can indicate proteinuria, abnormal tubular reabsorption, and glomerular filtration barrier injury, respectively. Urine sampling is relatively convenient and suitable for dynamic monitoring, but urine volume, urinary creatinine correction, and sample stability should be considered.

(4) Regulatory system indicators

Indicators such as Renin can be used to evaluate changes related to the renin-angiotensin system and are suitable for studies of hypertensive renal injury, renal blood flow regulation, and chronic kidney disease progression. These indicators are usually not used as independent renal injury endpoints, but are more suitable as mechanistic supplements.

1.2 Sample Types and Indicator Selection

(1) Serum or plasma samples

Serum or plasma samples are suitable for detecting systemic indicators such as creatinine, Cystatin C, β2-microglobulin, and Renin, and can be used to evaluate overall renal function and circulating changes.

(2) Urine samples

Urine is suitable for detecting indicators such as KIM-1, NGAL, urinary protein, β2-microglobulin, and Nephrin. Urinary biomarkers are closer to local changes in renal tubules and the filtration barrier, but concentration correction is required.

(3) Tissue and cell samples

Renal tissue or renal tubular epithelial cell models are suitable for detecting KIM-1, NGAL, Cystatin C, inflammatory factors, and injury pathway proteins, and can be used for mechanistic studies and intervention validation.

2 Common Renal Function Biomarkers

2.1 Creatinine and Traditional Renal Function Indicators

(1) Serum creatinine

Creatinine is derived from creatine metabolism and is mainly excreted through glomerular filtration. Elevated serum creatinine usually indicates decreased filtration function, but it may lag behind in early kidney injury. In experiments, animal body weight, muscle mass, dosing time, and urinary indicators should be interpreted comprehensively.

(2) Urinary creatinine

Urinary creatinine can be used for correction of urinary biomarkers. For example, urinary KIM-1, urinary NGAL, and urinary protein are often normalized to urinary creatinine to reduce bias caused by urine concentration or dilution.

(3) Urinary protein

Elevated urinary protein suggests glomerular filtration barrier abnormalities or reduced tubular reabsorption capacity. If only total urinary protein is measured, it is difficult to distinguish the injury site, and it should be interpreted together with Nephrin, β2-microglobulin, or histological results.

2.2 Cystatin C

Cystatin C is a low-molecular-weight protein commonly used to evaluate glomerular filtration function. Compared with creatinine, Cystatin C is less affected by muscle mass and provides supplementary value in some studies of early renal function decline.

(1) Serum Cystatin C

Elevated serum Cystatin C usually indicates reduced filtration function. If creatinine has not increased significantly but Cystatin C has already changed, urinary injury biomarkers should be combined to determine whether early renal dysfunction is present.

(2) Combined use of Cystatin C and creatinine

Creatinine and Cystatin C reflect renal function from different perspectives. Their combined use can improve the interpretation of filtration function changes, especially in chronic kidney disease progression, mild renal function decline, and drug nephrotoxicity evaluation.

(3) Detection methods

Cystatin C can be analyzed by ELISA, immunoturbidimetry, Western blot, or antibody-based detection. In mechanistic studies, recombinant proteins and antibodies can also be used to verify assay specificity.

2.3 KIM-1

KIM-1, also known as TIM-1/HAVCR1, is a marker markedly upregulated after proximal tubular injury. Urinary KIM-1 is commonly used to evaluate renal tubular epithelial injury and is suitable for studies of drug-induced renal injury, ischemia-reperfusion injury, and toxicological models.

(1) Early injury response

KIM-1 can increase relatively early after proximal tubular injury, often before obvious changes in serum creatinine. If KIM-1 increases while creatinine remains unchanged, this may indicate an early injury stage or injury that has not yet caused overall filtration function decline.

(2) Model applicability

In cisplatin, gentamicin, ischemia-reperfusion, and some chemical toxicant models, KIM-1 can serve as a sensitive indicator of tubular injury. Species-specific ELISA kits should be selected for different species.

(3) Result interpretation

Increased KIM-1 indicates a tubular injury response, but it does not independently represent complete renal function loss. NGAL, urinary protein, histopathology, and serum creatinine should be integrated for analysis.

2.4 NGAL

NGAL, also known as Lipocalin-2, is a commonly used early biomarker in acute kidney injury research and can increase under renal tubular injury, inflammation, and stress conditions. It can be detected in serum, urine, or cell culture supernatant.

(1) Acute kidney injury evaluation

Elevated NGAL often indicates acute tubular stress or injury response and is suitable for dynamic monitoring within a short time window. Compared with creatinine, NGAL is more closely related to early injury signals.

(2) Inflammation-related interference

NGAL is also associated with inflammation and immune cell responses. Therefore, in infection, inflammation, or systemic stress models, NGAL changes should not be interpreted entirely as kidney-specific injury.

(3) Value of combined detection

Combined detection of NGAL and KIM-1 can improve the reliability of tubular injury assessment. KIM-1 is more biased toward proximal tubular injury, while NGAL is more suitable for reflecting acute injury and stress responses.

2.5 β2-Microglobulin

β2-microglobulin can be filtered through the glomerulus and is associated with proximal tubular reabsorption function. Elevated urinary β2-microglobulin often indicates tubular reabsorption dysfunction or tubular injury.

(1) Urine detection

Urinary β2-microglobulin is suitable for evaluating changes in tubular function. Sample storage conditions and urine pH may affect detection stability and should be controlled during experimental design.

(2) Serum detection

Serum β2-microglobulin can be affected by renal function, immune status, and cell turnover. If used in renal function research, it should be interpreted together with urinary indicators and other renal function endpoints.

2.6 Nephrin, Nephronectin, and Renin

(1) Nephrin

Nephrin/NPHN is associated with the slit diaphragm structure of podocytes. Changes in NPHN in urine or samples can help evaluate glomerular filtration barrier injury and podocyte damage.

(2) Nephronectin

Nephronectin/NPNT is associated with the glomerular basement membrane and extracellular matrix, and can serve as a supplementary indicator in studies of structural changes and matrix remodeling.

(3) Renin

Renin reflects regulation related to the renin-angiotensin system. It is more suitable for mechanistic studies of hypertensive renal injury, renal blood flow regulation, and chronic kidney disease, and should not replace creatinine, Cystatin C, or urinary injury biomarkers.

Table 1 Functional Classification of Renal Function Biomarkers

Biomarker Category	Representative Indicators	Main Sample Types	Reflected Information	Applicable Research Scenarios
Filtration function indicators	Creatinine, Cystatin C	Serum, plasma, urine	Changes in glomerular filtration function	Renal function screening, chronic kidney disease, drug nephrotoxicity
Tubular injury indicators	KIM-1, NGAL	Urine, serum, tissue, cell culture supernatant	Tubular epithelial injury and stress response	Acute kidney injury, toxicology, ischemia-reperfusion
Tubular reabsorption indicators	β2-microglobulin	Urine, serum	Proximal tubular reabsorption function	Tubular injury, abnormal protein handling
Filtration barrier indicators	Urinary protein, NPHN	Urine, serum, tissue	Glomerular barrier and podocyte injury	Proteinuria, glomerular lesions
Matrix and structural indicators	NPNT	Serum, tissue, cells	Glomerular matrix and structural changes	Chronic kidney disease, fibrosis, and matrix remodeling
Regulatory system indicators	Renin	Serum, plasma, tissue	RAAS-related regulation	Hypertensive renal injury, renal blood flow regulation

3 Detection Methods and Experimental Design

3.1 Serum and Urine Biochemical Detection

(1) Creatinine detection

Creatinine can be detected using the PA rate method, sarcosine oxidase method, or colorimetric method. For animal experiments, blood collection time, fasting status, sample processing, and detection platform should be standardized.

(2) Urinary protein detection

Urinary protein can be detected using the Ponceau colorimetric method or sulfosalicylic acid method. The colorimetric method is suitable for quantitative analysis, while qualitative methods are suitable for rapid screening. Urinary protein results should preferably be corrected using urinary creatinine or urine volume.

(3) Sample correction

Urine samples are greatly affected by water intake, urine volume, and collection time. Urinary indicators such as KIM-1, NGAL, β2-microglobulin, and urinary protein should preferably be corrected by urinary creatinine or 24-hour urine volume.

3.2 ELISA Detection

ELISA is suitable for quantitative detection of protein indicators such as Cystatin C, KIM-1, NGAL, β2-microglobulin, NPHN, NPNT, and Renin. Species-specific kits should be selected for different species to avoid unreliable results caused by differences in antibody recognition.

(1) Standard curve

The standard curve should cover the concentration range of the samples. If the sample concentration exceeds the detection range, the sample should be diluted and tested again.

(2) Sample matrix

Serum, urine, tissue homogenates, and cell culture supernatants have substantial matrix differences. Before testing, the applicable sample types of the kit should be confirmed, and blanks and quality control samples should be included.

(3) Inter-batch variation

The same experiment should be completed with the same batch of kits whenever possible. When comparing data across batches, internal quality control samples should be included.

3.3 Immunodetection and Mechanistic Validation

Antibodies and recombinant proteins can be used for Western blot, immunofluorescence, immunohistochemistry, and ELISA method validation. For proteins such as Cystatin C, NGAL, and KIM-1, recombinant proteins can serve as positive controls or standardized validation materials.

(1) Western blot

Western blot is suitable for verifying changes in specific biomarker protein expression in renal tissue or cell samples. Internal reference proteins and equal loading controls are required.

(2) Immunofluorescence/immunohistochemistry

Immunofluorescence and immunohistochemistry are suitable for observing the localization of biomarkers in glomeruli, proximal tubules, distal tubules, or interstitial regions, helping to interpret injury sites.

(3) Recombinant protein controls

Recombinant proteins can be used for antibody validation, standard curve establishment, and positive controls in detection systems, especially in method development and antibody specificity validation.

4 Indicator Combinations in Different Research Scenarios

4.1 Acute Kidney Injury Research

Acute kidney injury often requires early, dynamic, and site-related indicators. Serum creatinine alone may lag behind, and KIM-1, NGAL, and urinary protein should be combined for evaluation.

(1) Early stage

NGAL, KIM-1, and Cystatin C should be prioritized to capture early changes in tubular injury and filtration function.

(2) Progression stage

Serum creatinine, urinary protein, and β2-microglobulin can be added to determine whether injury affects overall renal function and tubular reabsorption capacity.

(3) Recovery stage

The decreasing trends of KIM-1 and NGAL should be dynamically monitored, while creatinine, urinary protein, and histopathological recovery should also be observed.

4.2 Chronic Kidney Disease Research

Evaluation of chronic kidney disease should focus on long-term decline in filtration function, proteinuria, podocyte injury, and matrix remodeling. Cystatin C, creatinine, urinary protein, NPHN, and NPNT can form a relatively complete indicator combination.

(1) Progression of filtration function

Creatinine and Cystatin C can be used for long-term tracking of renal function changes. If the trends of the two are inconsistent, body weight, muscle mass, and urinary injury markers should be considered.

(2) Proteinuria and barrier injury

Increased urinary protein suggests filtration barrier injury or tubular reabsorption abnormalities. If NPHN changes occur simultaneously, podocyte or glomerular barrier injury is more strongly supported.

(3) Structural remodeling

NPNT and histological results can be used to analyze glomerular matrix and structural changes, which are suitable for chronic progression models or fibrosis-related studies.

4.3 Drug-Induced Nephrotoxicity Research

Drug-induced nephrotoxicity often affects proximal tubules and may also affect glomeruli and renal blood flow regulation. Experimental design should cover functional, injury-related, and mechanistic indicators.

(1) Basic functional endpoints

Creatinine, Cystatin C, and urinary protein should be detected to evaluate overall renal function and changes in proteinuria.

(2) Tubular injury endpoints

KIM-1, NGAL, and β2-microglobulin should be detected to assess tubular injury and reabsorption dysfunction.

(3) Mechanistic endpoints

Histology, oxidative stress, inflammatory factors, apoptosis, and Renin-related indicators can be combined to further explain the mechanism of toxicity.

Table 2 Indicator Combinations in Different Research Scenarios

Research Scenario	Recommended Core Indicators	Supplementary Indicators	Interpretation Focus
Acute kidney injury	NGAL, KIM-1, Cystatin C	Creatinine, urinary protein, β2-MG	Early tubular injury and filtration function changes
Chronic kidney disease	Creatinine, Cystatin C, urinary protein	NPHN, NPNT, Renin	Long-term filtration decline, proteinuria, and structural changes
Drug-induced nephrotoxicity	Creatinine, KIM-1, NGAL	β2-MG, urinary protein, histopathology	Toxicity site, injury severity, and recovery
Glomerular injury	Urinary protein, NPHN, Cystatin C	Creatinine, NPNT	Filtration barrier and podocyte injury
Tubular injury	KIM-1, NGAL, β2-MG	Urinary protein, creatinine	Tubular epithelial injury and reabsorption abnormalities
Hypertensive renal injury	Creatinine, urinary protein, Renin	NPHN, NPNT	RAAS regulation, filtration barrier, and structural changes

5 Data Interpretation and Common Misconceptions

5.1 Normal Creatinine Does Not Mean No Kidney Injury

Creatinine is a routine renal function indicator, but it is not sensitive enough for early tubular injury. If KIM-1 or NGAL has increased while creatinine has not changed, early injury or localized tubular response should be considered.

5.2 Elevated NGAL Does Not Necessarily Originate Entirely from the Kidney

NGAL can be affected by inflammation, infection, and systemic stress. If the model has an obvious inflammatory background, urinary NGAL, renal tissue expression, and KIM-1 results should be combined to determine the renal contribution.

5.3 The Source of Increased Urinary Protein Needs to Be Distinguished

Elevated urinary protein may originate from glomerular filtration barrier injury or tubular reabsorption dysfunction. If increased urinary protein is accompanied by NPHN changes, glomerular/podocyte injury is more strongly supported. If it is accompanied by increased β2-MG and KIM-1, tubular injury should be considered.

5.4 ELISA Results Should Be Interpreted According to Sample Type

The meaning of the same biomarker differs in serum, urine, and tissue. For example, urinary KIM-1 more closely reflects release from tubular injury, while serum KIM-1 may be affected by circulating status and detection sensitivity. Interpretation should return to sample source and research purpose.

Table 3 Key Points for Interpreting Renal Function Biomarker Results

Result Pattern	Possible Indication	Recommended Additional Tests
Increased creatinine and increased Cystatin C	Decreased filtration function	Urinary protein, eGFR estimation, histopathology
Normal creatinine and increased KIM-1	Early or localized tubular injury	NGAL, β2-MG, renal tissue KIM-1
Increased NGAL with increased inflammatory indicators	Kidney injury with inflammation or non-renal interference	KIM-1, urinary NGAL, tissue localization
Increased urinary protein with NPHN changes	Glomerular filtration barrier or podocyte injury	Renal histopathology, NPNT, Cystatin C
Increased β2-MG and increased KIM-1	Proximal tubular injury and reabsorption dysfunction	Urinary creatinine correction, NGAL, histology
Renin changes with increased urinary protein	RAAS regulation associated with renal injury	Blood pressure, Ang II, renal fibrosis markers

6 Selection of Related Reagents and Materials

Table 4 Product Selection for Renal Function Biomarker Research

Cat. No.	Product Name	Specification/Purity	Application Module	Application Positioning
C108393	Creatinine	≥99%	Glomerular filtration function evaluation	Used as creatinine standard, method validation material, and calibration reference for serum/urine creatinine detection
C425006	Creatinine	10mM in Water	Creatinine standard solution	Used for creatinine standard curve preparation, quality control, and method development
C1505879	Creatinine (Cr) Content Assay Kit (PA Rate, Micro Method)	BioReagent	Creatinine content detection	Used to determine creatinine levels in micro-samples and evaluate glomerular filtration function
C1515992	Creatinine (Cr) Content Assay Kit (SOX, Micro Method)	BioReagent	Creatinine content detection	Used to analyze creatinine content in serum, urine, or tissue samples
C1515993	Creatinine (Cr) Content Assay Kit (SOX, Colorimetric Method)	BioReagent	Creatinine content detection	Used for colorimetric creatinine detection and routine renal function evaluation
Ab098648	Cystatin C Antibody	≥90%(SDS-PAGE), See COA	Cystatin C detection	Used for detecting Cystatin C protein expression and evaluating early changes in glomerular filtration function
Ab008364	Recombinant Cystatin C Antibody	Recombinant,ExactAb™,Validated,See COA	Cystatin C detection	Used for Cystatin C immunodetection and protein level validation
Ab326859	Recombinant Cystatin C Antibody	KD Validation	Cystatin C detection	Used for Cystatin C knockdown validation, Western blot, or immunoassay validation
rp169603	Recombinant Human Cystatin C Protein	Carrier Free,His Tag,≥95%(SDS-PAGE)	Cystatin C standard/control	Used for Cystatin C detection system establishment, positive control, and antibody validation
EJ1514664	Human Kidney Injury Molecule 1 (Kim1) ELISA Kit	BioReagent	KIM-1 detection	Used to determine KIM-1 levels in human samples and evaluate proximal tubular injury
EJ1512247	Rat Kidney Injury Molecule 1 (Kim-1) ELISA Kit	BioReagent	KIM-1 detection	Used for quantitative KIM-1 detection in rat kidney injury models
EJ1513088	Mouse Kidney Injury Molecule 1 (Kim-1) ELISA Kit	BioReagent	KIM-1 detection	Used for KIM-1 detection in mouse acute kidney injury and drug-induced renal injury models
rp176720	Recombinant Human TIM-1/KIM-1/HAVCR Protein	Animal Free,Carrier Free,His Tag,PBS Only,≥95%(SDS-PAGE)	KIM-1 standard/control	Used for KIM-1 antibody validation, ELISA method development, and positive control
Ab113231	Lipocalin-2/NGAL Mouse mAb	Carrier Free, ExactAb™, Azide Free, Validated, See COA	NGAL detection	Used for detecting Lipocalin-2/NGAL protein expression and evaluating acute tubular injury
Ab113226	NGAL Mouse mAb	≥90%(SDS-PAGE), See COA	NGAL detection	Used for NGAL immunodetection and protein level validation
Ab113225	NGAL Mouse mAb	≥90%(SDS-PAGE), See COA	NGAL detection	Used for NGAL-related Western blot, immunostaining, or method validation
Ab113227	Recombinant Lipocalin-2/NGAL Antibody	Recombinant, ExactAb™, Validated, See COA	NGAL detection	Used for high-specificity NGAL immunodetection and acute kidney injury biomarker research
rp148318	Recombinant Human Lipocalin-2/NGAL Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,Azide Free,His Tag,≥97%(SDS-PAGE)	NGAL standard/control	Used for NGAL detection system establishment, antibody validation, and positive control
rp176712	Recombinant Human Lipocalin-2/NGAL Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,His Tag,PBS Only,≥95%(SDS-PAGE)	NGAL standard/control	Used for human NGAL-related detection method development and functional studies
rp154312	Recombinant Mouse Lipocalin-2/NGAL Protein	Animal Free,Carrier Free,Bioactive,ActiBioPure™,His Tag,≥95%(SDS-PAGE)	NGAL standard/control	Used for NGAL detection system validation in mouse models
rp329641	Recombinant Rat NGAL Protein	≥90%(SDS-PAGE)	NGAL standard/control	Used as a detection control for NGAL in rat kidney injury models
EJ1513756	Human Neutrophil Gelatinase Associated Lipocalin (NGAL) ELISA Kit	BioReagent	NGAL quantitative detection	Used to detect NGAL levels in human serum, urine, or cell culture supernatant
EJ1511957	Rat Neutrophil Gelatinase Associated Lipocalin (NGAL) ELISA Kit	BioReagent	NGAL quantitative detection	Used for rat acute kidney injury or drug-induced nephrotoxicity models
EJ1512610	Mouse Neutrophil Gelatinase Associated Lipocalin (NGAL) ELISA Kit	BioReagent	NGAL quantitative detection	Used to evaluate NGAL levels in mouse kidney injury models
EJ1513702	Human Beta-2-Microglobulin (BMG/β2-MG) ELISA Kit	BioReagent	β2-MG detection	Used to detect β2-MG levels in human samples and evaluate tubular reabsorption function and tubular injury
EJ1511928	Rat Beta-2-Microglobulin (BMG/β2-MG) ELISA Kit	BioReagent	β2-MG detection	Used for renal function and tubular injury studies in rats
EJ1512582	Mouse Beta-2-Microglobulin (BMG/β2-MG) ELISA Kit	BioReagent	β2-MG detection	Used to evaluate tubular function and proteinuria-related changes in mouse models
EJ1511798	Monkey Beta-2-Microglobulin (BMG/β2-MG) ELISA Kit	BioReagent	β2-MG detection	Used for β2-MG detection in monkey samples and non-human primate renal function studies
H1506744	Urine Protein Content Assay Kit (Ponceau S, Colorimetric Method)	BioReagent	Urinary protein detection	Used for quantitative detection of total urinary protein and evaluation of proteinuria and glomerular barrier injury
U1506746	Urine Protein Assay Kit (Sulfosalicylic Acid Method)	BioReagent	Urinary protein screening	Used for qualitative urinary protein detection and rapid proteinuria screening
EJ1514666	Human Nephrin (NPHN) ELISA Kit	BioReagent	Podocyte injury detection	Used for Nephrin/NPHN detection in human samples and evaluation of glomerular filtration barrier injury
EJ1512249	Rat Nephrin (NPHN) ELISA Kit	BioReagent	Podocyte injury detection	Used for podocyte-related biomarker detection in rat glomerular injury models
EJ1513091	Mouse Nephrin (NPHN) ELISA Kit	BioReagent	Podocyte injury detection	Used to evaluate glomerular filtration barrier and podocyte injury in mouse models
EJ1514667	Human Nephronectin (NPNT) ELISA Kit	BioReagent	Glomerular matrix/structural biomarker detection	Used to detect Nephronectin/NPNT in human samples and assist in evaluating glomerular matrix and structural changes
EJ1514665	Human Renin (Renin) ELISA Kit	BioReagent	Renin-angiotensin system evaluation	Used to detect Renin levels in human samples and assist in evaluating renal endocrine regulation and RAAS status
EJ1512248	Rat Renin (Renin) ELISA Kit	BioReagent	Renin-angiotensin system evaluation	Used for Renin level detection in rat models
EJ1513089	Mouse Renin (Renin) ELISA Kit	BioReagent	Renin-angiotensin system evaluation	Used for Renin level detection in mouse models

7 Frequently Asked Questions

7.1 Is it sufficient to detect only creatinine in renal function research?

It is not recommended to detect only creatinine. Creatinine is suitable for evaluating overall filtration function, but it is not sensitive enough for early tubular injury. In studies of acute kidney injury or drug-induced nephrotoxicity, KIM-1, NGAL, Cystatin C, and urinary protein should be combined.

7.2 What is the difference between Cystatin C and creatinine?

Creatinine is more affected by muscle mass, age, sex, and diet, whereas Cystatin C is less affected by muscle mass and is more suitable as a supplementary indicator of filtration function decline. Using both together improves interpretation reliability.

7.3 What does simultaneous elevation of KIM-1 and NGAL indicate?

Simultaneous elevation of KIM-1 and NGAL usually suggests enhanced tubular injury or stress response. KIM-1 is more biased toward proximal tubular injury, while NGAL is more suitable for evaluating acute injury and inflammation-related responses.

7.4 Why should urinary biomarkers be corrected by urinary creatinine?

Urine concentration is affected by water intake, urine volume, and sampling time. Correction by urinary creatinine can reduce differences caused by urine dilution and improve comparability between samples.

7.5 What is β2-microglobulin suitable for evaluating?

β2-microglobulin is commonly used to evaluate proximal tubular reabsorption function and tubular injury. Increased urinary β2-MG is more indicative of tubular dysfunction, while serum β2-MG may be affected by both renal function and immune status.

7.6 Does increased urinary protein necessarily indicate glomerular injury?

Not necessarily. Increased urinary protein may result from glomerular filtration barrier abnormalities or tubular reabsorption dysfunction. NPHN, β2-MG, KIM-1, and histopathology should be combined to determine the injury site.

7.7 Is Renin suitable as a core indicator of renal injury?

Renin is not suitable as a standalone core indicator of renal injury. It is more appropriate as a supplementary indicator in studies of RAAS regulation, blood pressure-related renal injury, or chronic kidney disease mechanisms.

Renal function biomarker research should design indicator combinations from multiple dimensions, including filtration function, tubular injury, urinary protein changes, filtration barrier integrity, and renal regulatory systems. Creatinine and Cystatin C are suitable for evaluating filtration function; KIM-1 and NGAL are suitable for capturing early tubular injury; β2-MG, urinary protein, NPHN, and NPNT can further localize tubular reabsorption abnormalities, proteinuria, and glomerular structural changes.

For more related articles, please see below:

[1] Animal model of chronic aristolochic acid nephropathy

[2] Animal models of hyperuricemia and uric acid nephropathy

[3] Animal model of lupus-like nephritis

[4] Animal model of gentamicin nephropathy

[5] A new animal model of uric acid nephropathy

[6] Animal model of diabetic nephropathy

[7] Animal model of chronic renal failure