What is the appropriate management for a patient with chronic kidney disease (CKD) stage 3 or worse, anemia, and elevated eosinophil count, considering the patient's lab results show impaired renal function, hypocalcemia, and other hematological abnormalities?

Management of CKD Stage 3b with Anemia and Eosinophilia

This patient requires immediate iron studies evaluation and iron supplementation before considering erythropoiesis-stimulating agents (ESAs), while simultaneously investigating the cause of eosinophilia which may indicate an underlying inflammatory or autoimmune process affecting the kidneys. 1, 2

Immediate Anemia Management

Iron Status Assessment (Priority #1)

• Check transferrin saturation and serum ferritin immediately before any ESA consideration, as iron deficiency is the most common cause of treatment failure in CKD-related anemia 1, 2
• The patient's hemoglobin of 9.8 g/dL (98 g/L) is below the treatment threshold of 11 g/dL (110 g/L) recommended by KDIGO guidelines 1
• Iron supplementation should be initiated if ferritin <100 ng/mL or transferrin saturation <20% 1, 2, 3

Iron Supplementation Strategy

• Intravenous iron is preferred over oral iron in CKD patients, increasing hemoglobin by 7-10 g/L versus 4-7 g/L with oral supplementation 1
• For non-dialysis CKD stage 3 patients, either IV or oral iron is acceptable, though IV is more effective 3
• Oral iron should be taken with meals to minimize gastrointestinal discomfort and not within 2 hours of antibiotics 4

ESA Therapy Considerations

• Do not initiate ESAs until iron studies are checked and iron deficiency is addressed 1, 2
• Target hemoglobin should be 11-12 g/dL (110-120 g/L); avoid exceeding 13 g/dL as this increases cardiovascular mortality and stroke risk 1
• If ESAs are eventually needed, monitor hemoglobin every 2-4 weeks during dose titration 1

Evaluation of Eosinophilia

Differential Diagnosis Priority

The elevated eosinophil count (5.8%, absolute 0.50) in the context of CKD stage 3b requires investigation for:

• Acute interstitial nephritis (AIN) - a common cause of both eosinophilia and kidney dysfunction that is often underdiagnosed 5
• ANCA-associated vasculitis (specifically EGPA) - particularly important given the renal impairment and eosinophilia combination 5
• IgG4-related disease - an overlapping syndrome that can present with eosinophilia and kidney involvement 5
• Medication-induced AIN - review all current medications for potential nephrotoxins 5

Specific Workup for Eosinophilia

• Obtain urinalysis looking for eosinophiluria, white blood cell casts, and proteinuria patterns 5
• Check ANCA panel (MPO and PR3 antibodies) given the combination of eosinophilia and renal dysfunction 5
• Consider IgG4 levels if clinical suspicion warrants 5
• Review medication list for recent additions that could cause drug-induced AIN 5

Additional Laboratory Abnormalities

Hypocalcemia Management

• Calcium of 8.3 mg/dL is low and requires correction, particularly in CKD stage 3b where mineral bone disorder begins 6
• Check vitamin D (25-OH and 1,25-OH), phosphate, and intact PTH levels to assess CKD-mineral bone disorder 6

Anemia Workup Beyond Iron

• Obtain reticulocyte count to distinguish decreased RBC production from hemolysis or blood loss 2
• Check vitamin B12 and folate levels, as deficiencies impair hemoglobin synthesis and cause poor ESA response 1, 2
• Perform stool guaiac testing to exclude occult gastrointestinal bleeding, which is common in CKD and causes both anemia and iron depletion 1, 2

Nephrology Referral

This patient meets criteria for nephrology referral based on:

• eGFR of 38 mL/min/1.73m² (CKD stage 3b, approaching stage 4 threshold of <30) 6
• Persistent anemia requiring specialized management 6
• Eosinophilia suggesting possible glomerulonephritis or interstitial nephritis requiring kidney biopsy consideration 6, 5

The 2024 KDIGO guidelines recommend nephrology referral when eGFR <30 mL/min/1.73m² or when there are features suggesting specific kidney diseases requiring specialized evaluation 6

Common Pitfalls to Avoid

• Never start ESAs without checking iron studies first - this is the most common cause of treatment failure 1, 2
• Do not assume anemia is solely due to erythropoietin deficiency - 25-37.5% of CKD patients have concurrent iron deficiency 2
• Do not target hemoglobin >13 g/dL - this increases cardiovascular events without benefit 1
• Do not dismiss eosinophilia as incidental - it may indicate treatable causes of kidney disease like AIN or vasculitis that require urgent intervention 5
• Do not delay nephrology referral - late referral (within 1 year of dialysis) is associated with increased mortality 6