Diagnostic Criteria and Management of Nephrotic Syndrome

Core Diagnostic Criteria

• The American Journal of Kidney Diseases defines nephrotic syndrome by the triad of proteinuria exceeding 3.5 g/24 hours, hypoalbuminemia (<3.0 g/dL), and edema, often accompanied by hyperlipidemia and lipiduria 1
• For children, proteinuria is defined as ≥40 mg/h/m² or first morning UPCR of ≥2 g/g, according to the American Journal of Kidney Diseases 1
• Hypoalbuminemia is defined as serum albumin <3.0 g/dL in adults, as stated by the American Journal of Kidney Diseases and Kidney International 2, 3
• In children, hypoalbuminemia is traditionally defined as ≤2.5 g/dL, according to the American Journal of Kidney Diseases 1

Associated Features

• The American Journal of Kidney Diseases and Kidney International report that patients with nephrotic syndrome have an increased risk of thromboembolism, especially when serum albumin falls below 2.9 g/dL 2, 4

Diagnostic Evaluation

Laboratory Assessment

• The American Journal of Kidney Diseases recommends measuring serum albumin as part of the diagnostic evaluation 1
• The Nature Reviews Nephrology suggests performing a complete blood count, serum electrolytes, kidney function tests, lipid profile, thyroid function tests, serum IgG level, and calcium, phosphate, alkaline phosphatase, PTH, and vitamin D levels as part of the diagnostic evaluation 5

Imaging

• The Nature Reviews Nephrology recommends renal ultrasound to assess kidney echogenicity and size, abdominal ultrasound to evaluate for ascites, and cardiac ultrasound to check for effusions and left ventricular mass 5

Histopathology

• The Kidney International states that kidney biopsy is not routinely performed in children at initial presentation, but is indicated in children with steroid resistance 3

Special Considerations

• The American Journal of Kidney Diseases notes that the definition of nephrotic syndrome in children has traditionally used a lower albumin threshold (≤2.5 g/dL) compared to adults (<3.0 g/dL) 1
• The Kidney International reports that albumin assay variability can affect the diagnosis, with a serum albumin of 2.5 g/dL with bromocresol green (BCG) equaling approximately 2.0 g/dL with bromocresol purple (BCP) or immunonephelometry 3

Differential Diagnosis

• The Kidney International states that minimal change disease is the most common primary glomerular disease in children 3

Nephrotic Syndrome Diagnosis and Management

Diagnostic Criteria and Evaluation

• The Kidney Disease: Improving Global Outcomes (KDIGO) guideline defines severely increased albuminuria (A3) as uACR ≥300 mg/g (≥30 mg/mmol) 6
• In children, proteinuria ≥40 mg/h/m² or first morning UPCR of ≥2 g/g, serum albumin ≤2.5 g/dL, and edema are diagnostic criteria for nephrotic syndrome 7
• Serum albumin measurement is crucial, and the assay type (bromocresol green vs. bromocresol purple) should be noted 8

Differential Diagnosis and Biopsy Indications

• In children <12 years, minimal change disease is the most common cause of nephrotic syndrome, and initial treatment with glucocorticoids without biopsy is standard 8
• Kidney biopsy is recommended for children ≥12 years and adults to determine the underlying cause of nephrotic syndrome 8
• The American Journal of Kidney Diseases recommends kidney biopsy for adults, except in cases with positive serum anti-phospholipase A2 receptor antibodies (diagnostic of membranous nephropathy) 7

FSGS-Specific Evaluation and Risk Assessment

• For patients with FSGS on biopsy, classification into one of four categories (primary, genetic, secondary, or undetermined cause) guides treatment 9
• Venous thromboembolism risk assessment is crucial, particularly when serum albumin falls below 2.9 g/dL, and membranous nephropathy carries a higher VTE risk than other causes 7, 10
• The Kidney International guideline recommends considering risk assessment tools (e.g., http://www.med.unc.edu/gntools/) for venous thromboembolism risk assessment 8

Management and Monitoring

• Disease-specific therapy, based on biopsy findings and underlying cause, is recommended, and for primary causes, immunosuppressive therapy according to specific disease guidelines is suggested 9
• Regular assessment of proteinuria, serum albumin, and kidney function, as well as monitoring for complications (thromboembolism, infections), is essential 8
• The American Journal of Kidney Diseases recommends considering prophylactic anticoagulation in high-risk patients, particularly those with membranous nephropathy and serum albumin <2.9 g/dL 10

Diagnostic Approach for Nephrotic Syndrome

Initial Evaluation

• The American College of Radiology recommends complete blood count with platelets as part of the initial diagnostic workup for nephrotic syndrome 11
• The Infectious Diseases Society of America suggests evaluating complement levels (C3, C4) to assess for immune-mediated disease, and antinuclear antibody testing if systemic lupus erythematosus is suspected, as well as hepatitis B and C serologies to identify secondary causes 12

Secondary Cause Evaluation

• The American Journal of Kidney Diseases recommends suspecting secondary causes in cases of non-nephrotic range proteinuria (<3.5 g/day) with hypoalbuminemia, or nephrotic-range proteinuria but serum albumin >3.0 g/dL, and considering targeted testing based on clinical suspicion, including medication review to identify nephrotoxic agents 13
• The Infectious Diseases Society of America advises HIV testing, particularly in high-risk populations, as part of the secondary cause evaluation 12

FSGS-Specific Workup

• The American Journal of Kidney Diseases suggests genetic testing for patients with familial kidney disease, syndromic features, or steroid-resistant FSGS, and classification into categories to guide treatment, as well as documenting history of prematurity as potential etiology for reduced nephron number 13

Diagnostic Testing

• The American College of Radiology recommends renal ultrasound to assess kidney size and echogenicity, particularly before potential biopsy 11

Renal Biopsy Timing and Technical Requirements for Adult-Onset Nephrotic Syndrome

Biopsy Indications and Technical Requirements

• The American College of Rheumatology recommends performing a kidney biopsy within the first month after nephrotic syndrome onset, preferably before starting immunosuppressive treatment, to establish a specific histologic diagnosis and guide treatment selection 14, 15
• A biopsy sample should include at least 8 glomeruli for light microscopy with H&E, PAS, Masson's trichrome, and silver stain, as well as immunofluorescence for IgG, C3, IgA, IgM, C1q, κ and λ light chains 14, 15
• Electron microscopy is recommended to facilitate recognition of proliferative and membranous lesions, and to provide additional diagnostic information 14, 15
• The biopsy should be performed before initiating immunosuppressive therapy to avoid obscuring histologic changes, and to ensure that the treatment is tailored to the specific underlying cause of the nephrotic syndrome 14, 15
• In patients with advanced chronic kidney disease (GFR <30 mL/min/1.73 m²), biopsy may still be considered if there is evidence of active disease and kidney size is greater than 9 cm in length 14, 15

Nephrotic Syndrome Diagnosis and Management

Diagnostic Criteria and Evaluation

• The American College of Rheumatology recommends suspecting systemic lupus erythematosus in patients with nephrotic syndrome and checking ANA, anti-dsDNA, and complement levels 16, 17
• The National Kidney Foundation suggests that obesity may indicate secondary (maladaptive) FSGS, and genetic testing is indicated for familial kidney disease, syndromic features, or steroid-resistant FSGS 18

Complications Assessment and Management

• The American Journal of Kidney Diseases recommends considering prophylactic anticoagulation in high-risk patients with venous thromboembolism risk, particularly when serum albumin <2.9 g/dL, using validated risk assessment tools 19
• The American Journal of Kidney Diseases suggests that treatment doses of unfractionated or low-molecular-weight heparin or warfarin are preferred for anticoagulation, while factor Xa inhibitors and direct thrombin inhibitors are not recommended due to significant albumin binding and urinary losses 19
• The American College of Rheumatology recommends considering anticoagulant treatment in lupus nephritis with nephrotic syndrome and serum albumin <20 g/L 16, 17

Monitoring and Follow-up

• The Annals of the Rheumatic Diseases suggest monitoring patients with nephrotic syndrome every 2-4 weeks for the first 2-4 months, and then every 3-6 months for renal and extra-renal disease activity and comorbidities 16, 17

Hypercholesterolemia in Nephrotic Syndrome

Clinical Characteristics and Complications

• The American Academy of Pediatrics and other guideline societies imply that nephrotic patients have a four times greater risk of accelerated coronary heart disease due to metabolic complications, including hypercholesterolemia 20
• Patients with nephrotic syndrome, characterized by hypoalbuminemia and proteinuria, face additional risks including thromboembolism, infections, and potential progression to end-stage renal disease, with a 29% risk for renal vein thrombosis when albumin is low 20

Nephrotic Syndrome Management

Diagnostic Evaluation

• The Kidney International recommends assessing for hyperlipidemia, including total cholesterol, LDL-C, HDL-C, triglycerides, apolipoprotein B, and lipoprotein(a), in patients with nephrotic syndrome 21
• The American Journal of Kidney Diseases suggests screening for viral-induced glomerular disease with hepatitis B and C serologies, HIV testing, antinuclear antibody (ANA) and anti-dsDNA, and complement levels (C3, C4) in patients with nephrotic syndrome 22
• The American Journal of Kidney Diseases also recommends serum and urine immunoelectrophoresis/immunofixation plus serum free light chains for all adults to exclude paraprotein-related disease 22

Treatment Approach

• The Kidney International recommends RAS inhibition with ACE inhibitors or ARBs to reduce proteinuria and blood pressure in patients with nephrotic syndrome 21
• The Kidney International suggests considering statin therapy for persistent hyperlipidemia, particularly with other cardiovascular risk factors, and aligning intensity to ASCVD risk 21
• The Kidney International recommends warfarin as the anticoagulant of choice for documented thromboembolic events, with a target INR of 2-3 and frequent monitoring 23
• The Kidney International advises against using Factor Xa inhibitors and direct thrombin inhibitors for anticoagulation in nephrotic syndrome due to unpredictable pharmacokinetics 23

Disease-Specific Immunosuppression

• The Kidney International recommends cyclosporin as an alternative treatment for minimal change disease, with a starting dose of 2 mg/kg/day and gradual increase to a maximum of 4-6 mg/kg/day based on pharmacokinetic monitoring 24
• The Kidney International suggests continuing cyclosporin for a minimum of 6 months, with slow tapering by 0.5 mg/kg/month after complete remission, and maintaining for 1-2 years 24

Nephrotic Syndrome Management

Rationale Against Albumin Infusion

• The KDIGO guidelines do not recommend albumin infusion as part of standard nephrotic syndrome management, focusing instead on diuretics, antiproteinuric therapy with RAS inhibition, and disease-specific immunosuppression 25, 26, 27

Appropriate Management Strategy

Critical Anticoagulation Consideration

• The KDIGO 2021 recommends considering prophylactic full-dose anticoagulation when serum albumin is <20-25 g/L AND the patient has additional risk factors such as proteinuria >10 g/day 25, 26, 27
• Warfarin is the anticoagulant of choice with target INR 2-3, requiring frequent monitoring due to fluctuating albumin-protein binding 25, 28, 29

Disease-Specific Therapy

• Initiate immunosuppressive therapy based on biopsy findings - the definitive treatment to reduce proteinuria and allow albumin recovery 30

Common Pitfalls to Avoid

Monitoring Requirements

• Assess for thromboembolism risk factors beyond just albumin level: BMI >35 kg/m², heart failure, recent surgery, or prolonged immobilization 25, 26, 27

Nephrotic Syndrome Diagnosis and Management

Diagnostic Criteria and Laboratory Assessment

• The Kidney International guideline recommends that the biopsy sample must include at least 8 glomeruli for light microscopy with H&E, PAS, Masson's trichrome, and silver stain 31
• Immunofluorescence for IgG, C3, IgA, IgM, C1q, κ and λ light chains is necessary for diagnosis 31
• Electron microscopy is required to facilitate recognition of proliferative and membranous lesions 31
• Loop diuretics, such as furosemide, are commonly used for edema control 31
• Target blood pressure should be ≤125/80 mmHg 31

Disease-Specific Immunosuppression

• The Kidney International guideline recommends prednisone 1 mg/kg/day (maximum 80 mg) or alternate-day dose of 2 mg/kg (maximum 120 mg) as first-line therapy for primary FSGS with nephrotic syndrome 32, 33, 34, 31
• Cyclosporine or tacrolimus may be used as alternative first-line therapy for patients with contraindications to corticosteroids 34, 31
• Cyclosporine may be preferred over tacrolimus due to lesser tendency to precipitate diabetes 31

FSGS-Specific Evaluation and Treatment

• The Kidney International guideline recommends classification of FSGS into one of four categories to guide treatment: primary FSGS, genetic FSGS, secondary FSGS, and FSGS of undetermined cause 32, 33
• Genetic testing should be considered for familial kidney disease, syndromic features, steroid-resistant FSGS, and early-onset cases 31

Guideline‑Based Diagnosis of Nephrotic Syndrome

1. Initial Clinical Screening

• Exclude benign causes of periorbital or peripheral edema such as menstrual cycle changes, intense exercise, recent sexual activity, or trauma when evaluating suspected nephrotic syndrome. 35

2. Quantitative Assessment of Proteinuria

• Perform a dipstick urinalysis as the first screening step; a result of ≥ 1+ protein mandates quantitative confirmation. 35
• Quantify proteinuria using a urine protein‑to‑creatinine ratio (UPCR) or albumin‑to‑creatinine ratio (ACR) on a first‑morning specimen. 36
• A UPCR > 300–350 mg/mmol (≈ 2 g/g in children) defines nephrotic‑range proteinuria; an ACR ≥ 300 mg/g (≥ 30 mg/mmol) denotes severe albuminuria (A3). 36
• Confirm nephrotic‑range proteinuria with a 24‑hour urine collection; total protein excretion > 3.5 g/24 h in adults meets the diagnostic threshold. 35

3. Baseline Laboratory Evaluation

• Obtain a complete blood count with differential and platelet count as part of the initial work‑up. 37
• Assess renal function with serum creatinine, blood urea nitrogen, electrolytes, and calculate estimated glomerular filtration rate. 38
• Measure lactate dehydrogenase (LDH) and β2‑microglobulin to gauge disease activity or tumor burden when relevant. 38

4. Screening for Secondary Causes

• Test fasting glucose and HbA1c to identify diabetes mellitus, the most common secondary cause of adult nephrotic syndrome. 39
• Perform autoimmune serology—including ANA, anti‑dsDNA, and complement components C3, C4, and C1q—to evaluate for systemic lupus erythematosus. [37][40]
• Check hepatitis B and C serologies to rule out viral‑related glomerulopathies. 37
• Review the patient’s medication list to detect potential nephrotoxic agents. 39
• Obtain a detailed family history to uncover hereditary kidney diseases. 39
• Document body‑mass index; obesity (BMI > 35 kg/m²) is associated with secondary or maladaptive focal segmental glomerulosclerosis. 39

5. Urine Sediment Microscopy

• Examine urine sediment for dysmorphic red blood cells; > 80 % dysmorphic RBCs suggest glomerular hemorrhage. [37][35]
• Identify red‑cell casts, which are virtually pathognomonic for glomerulonephritis. [37][35]

6. Kidney Biopsy: Indications and Timing

• Kidney biopsy is the gold‑standard diagnostic tool for glomerular disease and should be performed within the first month after onset of nephrotic syndrome, ideally before initiating immunosuppressive therapy. 41
• In adults, biopsy is indicated for all cases of nephrotic syndrome except when serum anti‑phospholipase A2 receptor antibodies (PLA2R‑Ab) are positive, indicating primary membranous nephropathy. 41
• Additional adult indications include MPO‑positive or PR3‑positive ANCA vasculitis, Fabry disease, and genetically characterized familial FSGS. 41
• In children < 12 years with a typical presentation (most commonly minimal change disease), routine biopsy is not required; it is reserved for steroid‑resistant disease or for children ≥ 12 years. 41

7. Biopsy Technical Requirements

• Obtain a specimen containing at least 8–10 glomeruli for light‑microscopy stains (H&E, PAS, Masson’s trichrome, and silver). 41
• Perform immunofluorescence studies for IgG, C3, IgA, IgM, C1q, and κ/λ light chains. 41
• Conduct electron microscopy to detect proliferative or membranous lesions and to assess podocyte foot‑process effacement. 41

8. Histologic Classification and Management Guidance

• Classify biopsy results into categories such as minimal change disease, focal segmental glomerulosclerosis (primary, genetic, secondary, or undetermined), membranous nephropathy, or other glomerulopathies. 39
• For focal segmental glomerulosclerosis, further stratify into four histologic/clinical subgroups to guide therapeutic decisions. 39

HIV Testing in Tuberculosis‑Associated Nephrotic‑Range Proteinuria

Diagnostic Evaluation

• In patients with active tuberculosis who present with nephrotic‑range proteinuria, HIV serology should be performed to exclude HIV‑associated nephropathy (HIVAN), because HIVAN can produce a similar proteinuria pattern and TB‑HIV co‑infection is common. 42

First‑Line Corticosteroid Therapy for Primary Focal Segmental Glomerulosclerosis with Nephrotic Syndrome

Initial Supportive Care

• ACE‑inhibitor or ARB therapy should be employed to lower proteinuria and achieve a blood‑pressure target of ≤125/75 mmHg in patients with primary FSGS and nephrotic syndrome. 43

Corticosteroid Regimen (KDIGO 2021)

• High‑dose oral prednisone (1 mg/kg/day, maximum 80 mg, or 2 mg/kg on alternate days, maximum 120 mg) is recommended as first‑line treatment for a minimum of 4 weeks and up to 16 weeks, or until complete remission is attained, followed by a gradual taper to complete a 6‑month total course. 44, 45
• An early decline in proteinuria within the first 4–8 weeks predicts likely steroid responsiveness. 45
• If proteinuria remains high after 8–12 weeks or steroid‑related toxicity becomes significant, clinicians should consider switching to a calcineurin inhibitor rather than extending steroid exposure to the full 16 weeks. 44, 45
• After complete remission, continue the high‑dose regimen for an additional 2 weeks, then reduce prednisone by 5 mg every 1–2 weeks to finish a 6‑month treatment period. 44, 45
• After partial remission achieved at 8–12 weeks, maintain steroids until week 16, then taper by 5 mg every 1–2 weeks over the subsequent 6 months. 44, 45

Calcineurin Inhibitor (CNI) Therapy (KDIGO 2021)

Indications

• Transition to a CNI is indicated for steroid‑resistant disease (no response after 16 weeks), steroid intolerance, or unacceptable steroid toxicity. 43

Dosing and Therapeutic Targets

• Cyclosporine – start 2–3 mg/kg/day in two divided doses; titrate up to 4–5 mg/kg/day based on response; aim for a trough (C0) level of 100–175 ng/mL (or C2 < 500 ng/mL). 45, 43
• Tacrolimus – start 0.05–0.1 mg/kg/day in two divided doses; target trough level 5–10 ng/mL. 45
• Maintain target trough levels for at least 4–6 months before declaring treatment failure. 45
• If remission is achieved, continue CNI therapy for a minimum of 12 months, then slowly taper by ≈0.5 mg/kg per month to the lowest effective dose, with maintenance for 1–2 years thereafter. 43, 45

Safety Monitoring

• Monitor serum creatinine; if it rises >30 % from baseline and does not plateau, reduce the CNI dose, and discontinue the drug if the rise persists despite dose reduction. 45
• Perform a renal biopsy when it is unclear whether rising creatinine reflects CNI nephrotoxicity or disease progression. 43

Definitions of Treatment Response

• Partial remission – ≥ 50 % reduction in proteinuria, which still confers clinical benefit and should be maintained with the lowest effective CNI dose. 43
• Failure to achieve ≥ 50 % proteinuria reduction after 6 months of CNI therapy indicates non‑response and warrants alternative agents or referral to an expert center. 43

Management of Treatment‑Resistant Disease

• For patients who fail both corticosteroids and CNI, adding or switching to cyclophosphamide or mycophenolic acid is recommended. 44
• Accepting a stable partial remission may be preferable to escalating to more toxic regimens. 45

Guideline Authority

• The KDIGO 2021 guidelines provide the current evidence‑based framework for managing primary focal segmental glomerulosclerosis with nephrotic syndrome, superseding earlier recommendations. 44, 45

Calcineurin Inhibitor Therapy for Primary FSGS

Indications for Calcineurin Inhibitors

• Steroid dependence (relapse when tapering steroids) warrants initiation of a calcineurin inhibitor in adults with primary focal segmental glomerulosclerosis. 46

Dosing and Therapeutic Monitoring

Cyclosporine

• Begin cyclosporine at 2–3 mg/kg/day divided twice daily, and titrate upward to 4–5 mg/kg/day according to clinical response and tolerability. 46
• Aim for a trough (C0) concentration of 100–175 ng/mL (or a C2 level < 500 ng/mL) to achieve adequate immunosuppression. 46
• Maintain target drug levels for at least 4–6 months before labeling the regimen a failure. If remission is attained, continue cyclosporine for a minimum of 12 months, then taper slowly by 0.5 mg/kg per month to the lowest effective dose, with therapy sustained for 1–2 years. 46

Definitions of Treatment Response

• Partial remission: ≥ 50 % reduction in proteinuria from baseline, providing clinical benefit and requiring maintenance with the lowest effective calcineurin inhibitor dose. 46
• Treatment failure: < 50 % reduction in proteinuria after 6 months of calcineurin inhibitor therapy at target drug levels. 46

Practical Pitfalls and Management

• Rapid CNI tapering after remission can trigger swift relapse; therefore, taper should be gradual over 6–12 months, reaching the minimum effective dose and maintaining therapy for 1–2 years to preserve remission. 46

Renal Biopsy Guidelines for Nephrotic and Nephritic Syndromes

1. Indications for Performing a Kidney Biopsy

• Kidney biopsy is the gold‑standard diagnostic tool for glomerular diseases presenting with nephrotic or nephritic syndrome and should be performed whenever the result is expected to modify therapy or provide essential prognostic information, except in cases where serologic testing or a classic clinical picture permits empiric treatment. 47, 48
• A biopsy is warranted when the histologic diagnosis is likely to change management or supply prognostic data that cannot be obtained through non‑invasive methods. 47, 48
• The decision to biopsy hinges on whether tissue diagnosis will alter the therapeutic approach or risk‑stratification plan. 47

2. Situations Where Biopsy May Be Deferred (Serology‑Driven Exceptions)

3. Technical Requirements for an Adequate Biopsy

• Glomerular count: The core specimen must contain at least 8–10 glomeruli for light‑microscopy evaluation to reliably diagnose or exclude specific histopathologic patterns. 47, 48
• Mandatory complementary modalities:
• Focal and segmental lesions (e.g., FSGS): Additional tissue may be required to capture the affected glomerular segments and ensure diagnostic accuracy. 47

Evidence strength for the above technical recommendations is not explicitly graded in the source material.

Laboratory Evaluation of Suspected Nephrotic Syndrome

Core Diagnostic Laboratory Tests

• A comprehensive initial laboratory panel—including 24‑hour urine protein quantification, serum albumin, complete metabolic panel, lipid profile, complete blood count, and targeted serologic studies—should be ordered to confirm nephrotic syndrome and to screen for secondary causes. [49][50]
• 24‑hour urine collection is the gold‑standard method for quantifying protein loss; nephrotic‑range proteinuria in adults is defined as ≥ 3.5 g per 24 h. 50
• When a 24‑hour collection is impractical, a first‑morning spot urine protein‑to‑creatinine ratio (PCR) can be used; a PCR > 300–350 mg/mmol indicates nephrotic‑range proteinuria. 50
• Urinalysis with microscopy: the presence of > 80 % dysmorphic red blood cells or red‑cell casts suggests glomerulonephritis rather than isolated nephrotic syndrome. 49
• Serum albumin < 3.0 g/dL defines hypoalbuminemia in adults; note that the bromocresol‑green (BCG) assay reads ≈ 0.5 g/dL higher than the bromocresol‑purple (BCP) method. 51
• Serum creatinine and estimated glomerular filtration rate (eGFR) should be measured to assess baseline kidney function. [49][50]
• A complete metabolic panel (electrolytes, BUN, glucose, calcium, phosphate) is recommended to evaluate overall metabolic status. 49
• Complete blood count with differential and platelets helps detect anemia, infection, or hematologic malignancy that may mimic or coexist with nephrotic syndrome. 49

Secondary‑Cause Evaluation (Targeted Serologies)

• Autoimmune screening (ANA, anti‑dsDNA, complement C3 & C4) is indicated when clinical features raise suspicion for systemic lupus erythematosus or complement‑mediated glomerulonephritis. 49
• Viral serologies (hepatitis B surface antigen and hepatitis C antibody) should be obtained to identify viral‑associated glomerular disease. 49
• In adults, serum and urine protein electrophoresis with immunofixation plus serum free light‑chain analysis are mandatory to exclude monoclonal immunoglobulin‑related renal disease, which requires distinct management. [52][53]
• Anti‑phospholipase A2 receptor (PLA2R) antibody testing is recommended when membranous nephropathy is suspected; a positive result may eliminate the need for an immediate kidney biopsy in typical adult presentations. 54
• ANCA testing (anti‑MPO and anti‑PR3) should be performed if vasculitis is in the differential diagnosis. 49

Thromboembolism Risk Assessment

• When serum albumin falls below 2.5–2.9 g/dL, clinicians should assess additional VTE risk factors such as proteinuria > 10 g/day, body‑mass index > 35 kg/m², heart failure, recent surgery, or prolonged immobilization. 51
• Membranous nephropathy carries a particularly high risk of venous thromboembolism and warrants vigilant risk stratification. 51

Practical Considerations

• Albumin assay variability: laboratories must document the assay method used (BCG vs. BCP); a BCG result of 2.5 g/dL corresponds to roughly 2.0 g/dL by BCP, which can materially affect thromboembolism risk assessment and therapeutic decisions. 51
• Timing of laboratory assessment: baseline labs should be obtained before initiating immunosuppressive therapy to avoid obscuring diagnostic findings and to accurately gauge disease severity. 49
• Proteinuria quantification: random spot urine PCR exhibits high day‑to‑day variability; first‑morning specimens are preferred, and 24‑hour collections remain the gold standard when feasible. 50

Genetic Testing (When Indicated)

• Genetic testing should be considered in children with congenital nephrotic syndrome, a family history of kidney disease, syndromic features, or steroid‑resistant disease. 54
• In adults with steroid‑resistant focal segmental glomerulosclerosis, 11–24 % harbor pathogenic variants in podocyte‑ or type IV collagen‑related genes. 54