1.1 Presenting Clinical Data

The patient presented with a clinical syndrome characterized by progressive renal insufficiency and volume overload in the setting of prior evaluation by an outside oncologist for severe anemia. The following data were collected at the time of nephrology involvement:

Admission data: - Creatinine: 2.5 mg/dL (rising to 4.0 with aggressive diuresis) - Bicarbonate: 21 mEq/L (mild metabolic acidosis) - Albumin: 3.1 g/dL - Hemoglobin: 8.2 g/dL (prior range 7–9 g/dL, worked up by outside oncology) - Platelets: 192 × 10³/µL (normal) - Calcium: 8.8 mg/dL (normal) - Edema: 3+ bilateral - Urine albumin-to-creatinine ratio: >4 - Urine protein-to-creatinine ratio: 7.9 - Volume response: Minimal fluid removed with aggressive loop diuretic therapy; creatinine worsened

Subsequent evaluation: - Free light chain kappa: 17.4 mg/dL (= 174 mg/L) - Free light chain lambda: 3.24 mg/dL (= 32.4 mg/L) - κ/λ ratio: 5.37 - Echocardiogram: EF 45%, LVH, impaired relaxation (Grade I–II diastolic dysfunction) - BNP: 4,598 pg/mL - Troponin I: 59 ng/L - Monoclonal evaluation: Pending at time of nephrology consultation (no prior SPEP, immunofixation, or FLC had been obtained)

1.2 Initial Clinical Impression

The combination of massive albuminuria, hypoalbuminemia, preserved platelet count, normal calcium, and absent bone pain placed this patient outside the classical CRAB (hypercalcemia, renal failure, anemia, bone lesions) framework of symptomatic multiple myeloma. The outside oncologic workup had not specifically addressed plasma cell dyscrasia with renal-organ manifestation. Nephrology involvement reframed the presentation from “anemia workup with CKD” to a potential monoclonal gammopathy of renal significance (MGRS) or systemic AL amyloidosis.

3.1 Unit Conversion — A Critical Potential Error Source

Serum free light chains are measured and reported in mg/L at most reference laboratories, including Mayo Clinic. When values are reported in mg/dL (as in this case), conversion is mandatory before clinical interpretation:

1 mg/dL = 10 mg/L

The kappa of 174 mg/L is approximately 9× the upper limit of normal. The lambda of 32.4 mg/L is only mildly above the standard reference upper limit, and this mild elevation is entirely attributable to reduced renal clearance (kappa clears faster than lambda in normal renal function; impaired GFR raises both proportionally, but the smaller monomer kappa typically rises more in CKD as a non-clonal artifact).

3.2 Renal-Adjusted Reference Range

The standard κ/λ FLC reference range (0.26–1.65) was established in patients with normal renal function. In CKD, differential renal clearance of κ vs. λ light chains alters the ratio independent of clonality. The extended reference range for renal impairment is approximately 0.37–3.1. This patient’s ratio of 5.37 exceeds the renal-adjusted upper limit of 3.1, confirming a true clonal process rather than a CKD artifact (1,2).

3.3 Delta FLC (dFLC) Calculation

The dFLC (involved minus uninvolved FLC) = 174 − 32.4 = 141.6 mg/L

The measured dFLC is 174 − 32.4 = 141.6 mg/L, below the Mayo 2012 dFLC threshold of 180 mg/L. Heavy total proteinuria does not quantify urinary light-chain loss and cannot justify increasing the measured dFLC or treating it as an underestimated floor. Stage with the actual required biomarkers and assay definitions.

⚠️ Warning: In patients with heavy nephrotic-range proteinuria, serum FLC levels are spuriously lowered by urinary losses. The degree of clonal disease burden is likely greater than the serum FLC values imply. Do not use the dFLC alone to assess clone burden in this setting.

5.1 Biomarker Staging

The reported BNP and high-sensitivity troponin I indicate a concerning cardiac phenotype but are not interchangeable with the NT-proBNP and specified troponin assays of another staging system. Confirm amyloid diagnosis and apply a validated assay-specific scheme before assigning a stage or stage-based prognosis. CKD also affects biomarker interpretation.

An important caveat: this patient has a creatinine of 4.0 mg/dL. Natriuretic peptides are renally cleared, and NT-proBNP in particular rises as a function of reduced GFR. However, a BNP of 4,598 pg/mL far exceeds what renal failure alone produces. Published data suggest that in impaired renal function (CKD Stage III+), BNP thresholds for cardiac amyloid involvement shift to approximately 427 pg/mL — still orders of magnitude below this patient’s value. The biomarker elevation is cardiac, not purely renal (8).

5.2 Echocardiographic Reinterpretation

The echocardiogram showing EF 45%, LVH, and impaired relaxation was initially framed as hypertensive heart disease. The biomarker and hemodynamic findings warrant reassessment for infiltrative and other causes; a formal stage remains unconfirmed:

• EF 45% in cardiac amyloidosis does not represent mild systolic dysfunction — it represents the transition point where systolic reserve is becoming exhausted. Early cardiac amyloidosis presents with preserved EF; declining EF below 50% reflects progression into the systolic failure phase.
• “LVH” in amyloidosis is infiltrative pseudohypertrophy — amyloid fibrils depositing in the myocardial interstitium — not true myocyte hypertrophy driven by pressure overload. These walls appear thick but are physiologically hostile: stiff, non-compliant, and dependent on elevated filling pressures to maintain stroke volume.
• The echocardiogram should be re-read with a dedicated amyloid protocol including: posterior wall + septal thickness, mitral annular velocity (e’), E/e’ ratio, and most importantly global longitudinal strain (GLS) with apical sparing pattern. The relative apical sparing pattern on strain imaging (Bull’s-eye map) is highly specific for cardiac amyloidosis (sensitivity and specificity both exceeding 80%).

⚠️ Warning: A patient with suspected cardiac amyloidosis and EF 45% has already lost significant systolic reserve. Standard heart failure medications that reduce preload (aggressive diuretics), afterload (ACE-inhibitors, ARBs), or heart rate (beta-blockers, non-dihydropyridine calcium channel blockers) may be poorly tolerated or harmful. Cardiology co-management with amyloid expertise is required before titrating any cardiac medications.

5.3 The European IIIB Substage

The European modification of the Mayo staging system subdivides Stage III into IIIA (NT-proBNP 332–8,500 ng/L or BNP equivalent) and IIIB (NT-proBNP >8,500 ng/L). BNP and NT-proBNP are different molecules and not interchangeable by simple ratio, but a BNP of 4,598 pg/mL corresponds to a very high-risk profile. Whether this patient meets IIIB criteria requires NT-proBNP confirmation. Stage IIIB disease carries a median survival of approximately 5 months — the extreme high-risk category where speed of hematologic response is the dominant modifiable outcome predictor.

7.1 Why Diuresis Failed

Creatinine rising from 2.5 to 4.0 during aggressive loop diuretic therapy with minimal fluid removal is the pathognomonic hemodynamic signature of advanced cardiorenal amyloidosis:

1. Oncotic failure: With albumin at 3.1 g/dL, plasma oncotic pressure is insufficient to draw interstitial edema fluid back into the intravascular compartment. Diuresis removes intravascular volume faster than it can be refilled.
2. Stiff ventricle dependence on preload: The amyloid-infiltrated left ventricle requires elevated filling pressures to maintain stroke volume. Reduction of preload through diuresis drops cardiac output, reducing renal perfusion.
3. Tubular light chain toxicity: Loop diuretics concentrate tubular fluid, potentially increasing tubular light chain concentration and promoting Tamm-Horsfall protein binding — the same mechanism driving cast nephropathy. In a patient with heavy kappa light chain burden, aggressive furosemide may simultaneously worsen tubular injury.

7.2 Right Heart Catheterization — The Case For and Against

The diagnostic question (is this cardiac amyloidosis?) is answered. RHC is not needed to establish the diagnosis.

The management question (how do we safely manage volume?) remains open. RHC is justified to define: - Cardiac output and index (CI <2.0 L/min/m² confirms low-output state driving pre-renal AKI) - Right atrial pressure and PCWP (defining safe operating filling pressures) - Pulmonary vascular resistance (relevant if cardiac transplant consideration arises later)

If CI is markedly reduced, the appropriate response is not diuretic escalation but rather a shift to slow ultrafiltration or continuous renal replacement therapy with carefully defined net negative fluid removal rates that the ventricle can tolerate.

⚠️ Warning: Screen for Factor X deficiency before any invasive procedure. Systemic AL amyloid fibrils adsorb and sequester clotting Factor X, producing an acquired Factor X deficiency in up to 14% of AL amyloidosis patients. This causes procedure-related hemorrhage risk independent of platelet count and INR. A Factor X activity level should be sent before kidney biopsy or RHC.

9.1 Standard of Care: Dara-VCd

The ANDROMEDA phase 3 randomized controlled trial established daratumumab, bortezomib, cyclophosphamide, and dexamethasone (Dara-VCd) as the first FDA-approved therapy for newly diagnosed AL amyloidosis (January 2021). In 388 patients, the addition of subcutaneous daratumumab to VCd resulted in a hematologic complete response rate of 53.3% versus 18.1% in the VCd-alone arm, with significantly superior survival free from major organ deterioration or hematologic progression (5).

Key ANDROMEDA eligibility nuances relevant to this patient: - Patients with cardiac Stage IIIB (NT-proBNP >8,500 ng/L) were excluded from ANDROMEDA — this patient’s NT-proBNP equivalent needs verification - eGFR ≥20 mL/min was required — this patient’s current eGFR is borderline - Symptomatic multiple myeloma (meeting CRAB criteria) was an exclusion

These nuances underscore why a hematologist with specific AL amyloidosis expertise — not general oncology — is required for treatment planning. The dosing of bortezomib and cyclophosphamide, the management of fluid overload from IV infusions, and the decision-making around early mortality risk all require specialized experience.

9.2 Three Pillars of Outcome Improvement

Three pillars have been identified for improving AL amyloidosis outcomes: 1. Early disease recognition before advanced organ damage — partially failed here (delayed diagnosis with Cr already 4.0 and concerning cardiac involvement) 2. Rapid and deep hematologic response — the dominant modifiable variable going forward 3. Comprehensive multi-specialty supportive care — cardiology, nephrology, hematology working in parallel, not sequentially

9.3 Supportive Care Considerations

• Diuresis: Hold or dramatically reduce; if volume management is mandatory, consider ultrafiltration after RHC-guided hemodynamic assessment.
• Albumin infusions: Physiologically intuitive but not proven to improve outcomes; may precipitate pulmonary edema if cardiac function is compromised — use with caution and only with cardiac monitoring.
• Avoid: ACE inhibitors, ARBs, beta-blockers, non-dihydropyridine calcium channel blockers (poorly tolerated with amyloid cardiomyopathy).
• Coagulopathy surveillance: Factor X level, CBC, INR before procedures.
• Renal support: If creatinine continues to rise and the patient cannot tolerate adequate fluid removal for pulmonary protection, early renal replacement therapy planning should begin.