What is the best course of management for a patient with impaired renal function, hyperglycemia, anemia, hypocalcemia, and eosinophilia, along with abnormal RBC morphology?

Management of Impaired Renal Function with Hyperglycemia, Anemia, Hypocalcemia, and Eosinophilia

This patient requires immediate evaluation for multiple myeloma given the constellation of renal insufficiency (eGFR 53.72), anemia (Hb 10.7), hypocalcemia (8.4), and abnormal RBC morphology with macrocytosis, which collectively suggest a plasma cell dyscrasia until proven otherwise. 1

Immediate Diagnostic Workup

Multiple Myeloma Evaluation (Priority)

• Obtain serum protein electrophoresis (SPEP), serum free light chain assay, and 24-hour urine protein electrophoresis immediately 1
• The combination of renal insufficiency (creatinine 1.10, eGFR 53.72) with anemia and hypocalcemia in the absence of clear alternative causes mandates evaluation for monoclonal gammopathy 1
• If proteinuria consists predominantly of light chains with high serum free light chain levels, renal biopsy may not be necessary; however, if the cause of renal insufficiency remains unclear, proceed with renal biopsy to assess for light chain cast nephropathy or monoclonal immunoglobulin deposition disease 1

Renal Function Assessment

• The eGFR of 53.72 mL/min/1.73 m² places this patient in CKD stage 3a, requiring screening for CKD complications 1
• Check serum calcium, phosphate, intact PTH, and 25-hydroxyvitamin D levels immediately, as these should be monitored at least every 3 months in patients with eGFR <60 mL/min/1.73 m² 1, 2
• The BUN/creatinine ratio of 19 is within normal range, making prerenal azotemia less likely as the primary etiology 1

Anemia Workup

• Perform comprehensive iron studies including transferrin saturation (TSAT) and serum ferritin before considering erythropoiesis-stimulating agents 3, 4
• The macrocytosis (MCV 100.7) with abnormal RBC morphology (burr cells, ovalocytes, anisocytosis) suggests either B12/folate deficiency or underlying bone marrow pathology 1
• Check vitamin B12 and folate levels, though deficiency rates are low (<4% for B12, <1% for folate in cancer patients); reserve testing for high clinical suspicion or when planning ESA therapy 1
• The reticulocyte count should be measured to assess bone marrow response and guide ESA therapy if needed 3, 2

Eosinophilia Investigation

• The absolute eosinophil count of 1.30 (17.0%) requires evaluation for parasitic infection, drug reaction, or hematologic malignancy
• In the context of possible multiple myeloma, eosinophilia may represent a paraneoplastic phenomenon

Initial Management Strategy

Renal Protection

• If multiple myeloma is confirmed, initiate bortezomib-containing regimen immediately to decrease production of nephrotoxic clonal immunoglobulin 1
• Bortezomib/dexamethasone regimens can be administered without renal dose adjustment even in severe renal impairment or dialysis 1
• Consider adding cyclophosphamide, thalidomide, or daratumumab as third agent, all of which do not require dose adjustment 1
• Avoid or use lenalidomide with extreme caution and dose reduction based on creatinine clearance; it requires adjustment in renal impairment 1

Hyperglycemia Management

• Glucose of 127 mg/dL indicates impaired fasting glucose or diabetes
• If metformin is being considered or currently used, it is NOT recommended for initiation in patients with eGFR between 30-45 mL/min/1.73 m², and this patient's eGFR of 53.72 allows continued use with annual eGFR monitoring 5
• Obtain eGFR at least annually; in elderly patients or those at risk for renal deterioration, assess more frequently 5
• If eGFR falls below 45 mL/min/1.73 m², reassess benefit-risk of continuing metformin 5

Anemia Management

• Do NOT initiate ESA therapy until iron deficiency is corrected and multiple myeloma workup is complete 3, 4
• Target hemoglobin depends on underlying diagnosis; if myeloma-related, treat underlying disease first 1
• If iron deficiency is confirmed (TSAT <20%, ferritin <100 mg/L), start oral iron supplementation for mild anemia in non-dialysis CKD 3
• Monitor hemoglobin every 3 months in patients with eGFR <60 mL/min/1.73 m² 3, 2

Hypocalcemia and Bone Health

• Calcium of 8.4 mg/dL is low and requires correction, particularly if multiple myeloma is diagnosed
• Check 25-hydroxyvitamin D levels, as deficiency is common in CKD and contributes to hypocalcemia and secondary hyperparathyroidism 2
• Avoid calcium-based phosphate binders to prevent inappropriate calcium loading and vascular calcification 2

Electrolyte Monitoring

• Monitor serum potassium closely, as patients with eGFR <60 mL/min/1.73 m² are at risk for hyperkalemia, especially if ACE inhibitors or ARBs are used 1
• The current potassium of 4.0 mEq/L is normal, but requires periodic reassessment 1
• Restrict dietary sodium to <2 g/day once volume status is optimized 1, 6

Critical Pitfalls to Avoid

• Do NOT delay multiple myeloma workup based on "atypical" presentation; renal disease occurs in 20-50% of myeloma patients and negatively affects outcomes 1
• Do NOT start ESA therapy before excluding iron deficiency and completing hematologic malignancy workup 3, 4
• Do NOT restrict protein intake to "protect the kidneys" in the absence of nephrotic syndrome; maintain 0.8 g/kg/day 6
• Do NOT use NSAIDs, which worsen renal function and increase hyperkalemia risk 6
• Do NOT initiate metformin if eGFR falls below 45 mL/min/1.73 m² without careful benefit-risk assessment 5
• Do NOT administer iodinated contrast without stopping metformin in patients with eGFR 30-60 mL/min/1.73 m²; re-evaluate eGFR 48 hours post-procedure 5

Ongoing Monitoring Plan

• Monitor serum creatinine, eGFR, calcium, phosphate, and electrolytes every 3 months 1, 2
• Monitor hemoglobin every 3 months 3, 2
• Measure vitamin B12 levels every 2-3 years in patients on metformin due to risk of deficiency 5
• If multiple myeloma is confirmed, monitor response to therapy with serial free light chains and SPEP 1