What is the most likely diagnosis and appropriate management for a patient with chronic kidney disease stage 3b (estimated glomerular filtration rate ≈37 mL/min/1.73 m²), prerenal azotemia (BUN/creatinine ratio 23), hyperchloremic metabolic acidosis (serum CO₂ 15 mm Hg, normal anion gap), hyperglycemia (glucose 149 mg/dL), and iron‑deficiency microcytic anemia (MCV 63 fL, hemoglobin 11.8 g/dL)?

Diagnosis and Management of CKD Stage 3b with Multiple Complications

This patient has chronic kidney disease stage 3b (eGFR 37 mL/min/1.73 m²) with hyperchloremic metabolic acidosis, iron-deficiency anemia, and prerenal azotemia requiring immediate evaluation of underlying causes, treatment of metabolic acidosis with sodium bicarbonate, iron supplementation, and optimization of volume status and blood pressure control.

Primary Diagnosis: CKD Stage 3b with Multiple Complications

The patient meets diagnostic criteria for CKD stage 3b based on eGFR of 37 mL/min/1.73 m², which represents approximately 60-65% loss of kidney function 1, 2. The elevated BUN/creatinine ratio of 23 suggests a prerenal component, though this is at the borderline of normal (typically >20 suggests prerenal azotemia) 3.

Key Laboratory Abnormalities Requiring Action:

• Hyperchloremic metabolic acidosis (CO₂ 15 mmol/L, chloride 115 mEq/L, normal anion gap 10) is the most urgent metabolic derangement requiring treatment 4, 5
• Microcytic anemia (MCV 63.2 fL, hemoglobin 11.8 g/dL) with iron deficiency pattern requires evaluation and supplementation 1
• Hyperglycemia (glucose 149 mg/dL) suggests diabetes or prediabetes as the likely underlying cause of CKD 1, 6
• Leukocytosis with left shift (WBC 8.5 with 91% segs, 3% bands, 1% metamyelocytes) suggests possible infection or inflammatory process requiring evaluation 3

Immediate Diagnostic Workup

Confirm CKD Diagnosis and Determine Etiology

• Measure urinary albumin-to-creatinine ratio (UACR) immediately on a random spot urine sample, as this is essential for CKD diagnosis confirmation, risk stratification, and treatment decisions 1, 6, 2
• Review historical eGFR measurements to confirm chronicity (>3 months duration) and distinguish CKD from acute kidney injury 6, 2
• Obtain hemoglobin A1c to confirm diabetes diagnosis, as the hyperglycemia combined with CKD stage 3b strongly suggests diabetic kidney disease 1, 6
• Evaluate for diabetic retinopathy through ophthalmologic examination, as its presence supports diabetic kidney disease diagnosis 1

Evaluate for Prerenal Component

• Assess volume status through jugular venous distention, peripheral edema, orthostatic vital signs, and recent weight changes 7, 3
• Review medication list for nephrotoxins including NSAIDs, ACE inhibitors, ARBs, and diuretics that may be contributing to prerenal azotemia 1, 6
• Evaluate for gastrointestinal losses or reduced oral intake that could explain the elevated BUN/creatinine ratio 3

Screen for CKD Complications

The following laboratory tests should be obtained immediately for CKD stage 3b 1, 6:

• Parathyroid hormone (PTH) and 25-hydroxyvitamin D levels, as secondary hyperparathyroidism occurs in 25-60% of patients with eGFR 30-60 mL/min/1.73 m² 1
• Serum phosphate (already obtained, currently normal at baseline)
• Iron studies including serum ferritin and transferrin saturation to confirm iron deficiency and guide replacement therapy 1
• Repeat complete blood count in 2-4 weeks to assess anemia trajectory 1

Management of Metabolic Acidosis

Initiate sodium bicarbonate therapy immediately for this patient with serum bicarbonate of 15 mmol/L, as metabolic acidosis at this severity is associated with muscle wasting, bone disease, CKD progression, and increased mortality 4, 8, 5.

Treatment Protocol:

• Target serum bicarbonate concentration of 22-24 mEq/L using oral sodium bicarbonate supplementation 4, 5
• Starting dose: Sodium bicarbonate 650 mg (approximately 8 mEq) three times daily, with dose titration based on repeat bicarbonate measurements 8, 5
• Monitor for complications including volume overload, hypertension exacerbation, and hypernatremia, particularly given the patient's CKD stage 3b 4, 5
• Recheck serum bicarbonate within 2-4 weeks after initiation to assess response and adjust dosing 8, 5

Dietary Modifications:

• Increase base-producing foods including fruits and vegetables while limiting acid-producing animal-sourced protein intake 8
• Maintain protein intake at 0.8 g/kg/day as recommended for non-dialysis CKD stage 3 1

Important Considerations:

Metabolic acidosis typically develops when eGFR decreases below 20-25 mL/min/1.73 m² (stage 4-5 CKD), but this patient has acidosis at eGFR 37 mL/min/1.73 m² 4, 5. This earlier presentation may indicate:

• Diabetic kidney disease, as patients with diabetes can develop more severe acidosis at higher eGFR levels 9
• Type 4 renal tubular acidosis (hyperchloremic, normal anion gap acidosis) which is common in diabetic nephropathy 4, 5
• Concurrent acute illness suggested by the leukocytosis with left shift 3

Management of Iron-Deficiency Anemia

Initiate oral iron supplementation after confirming iron deficiency with serum ferritin and transferrin saturation measurements 1.

Diagnostic Criteria for Iron Deficiency in CKD:

• Absolute iron deficiency: Transferrin saturation ≤20% with serum ferritin ≤100 μg/L (for non-dialysis CKD patients) 1
• The microcytosis (MCV 63.2 fL) with elevated RDW (18.2%) strongly suggests iron deficiency as the primary cause 1

Treatment Approach:

• Oral ferrous sulfate 325 mg (65 mg elemental iron) once or twice daily is first-line therapy for non-dialysis CKD patients 1
• Evaluate for gastrointestinal blood loss given the iron deficiency, particularly in the context of possible NSAID use or other bleeding sources 1, 3
• Consider upper and lower GI endoscopy if iron deficiency is confirmed and no other obvious cause is identified, as occult GI bleeding is common in CKD patients 1
• Recheck hemoglobin and iron studies in 8-12 weeks to assess response to therapy 1

Anemia Monitoring in CKD Stage 3b:

• Measure hemoglobin at least twice per year for patients with eGFR 30-59 mL/min/1.73 m² (CKD stage 3) 1
• Erythropoiesis-stimulating agents (ESAs) are not indicated at this hemoglobin level (11.8 g/dL) until iron deficiency is corrected and other causes are excluded 1

Blood Pressure and Cardiovascular Risk Management

Blood Pressure Target:

• Target blood pressure <130/80 mmHg for all CKD patients, particularly those with albuminuria 1, 6

Renin-Angiotensin System Blockade:

The decision to initiate or continue ACE inhibitor/ARB therapy depends on UACR results 1, 6:

• If UACR ≥300 mg/g: ACE inhibitor or ARB is strongly recommended regardless of blood pressure, with target to reduce albuminuria by ≥30% 1
• If UACR 30-299 mg/g AND hypertension: Initiate ACE inhibitor or ARB 1, 6
• If UACR <30 mg/g with normal blood pressure: ACE inhibitor/ARB is not recommended for primary prevention 1

Monitoring After ACE Inhibitor/ARB Initiation:

• Recheck serum creatinine and potassium 7-14 days after initiation or dose change 1
• Continue therapy if serum creatinine increases ≤30% in the absence of volume depletion 1, 6
• Discontinue if creatinine increases >30% or if hyperkalemia (potassium >5.5 mEq/L) develops 1

SGLT2 Inhibitor Therapy:

If diabetes is confirmed (HbA1c ≥6.5%), initiate SGLT2 inhibitor with demonstrated kidney and cardiovascular benefits (empagliflozin, canagliflozin, or dapagliflozin) as this patient's eGFR of 37 mL/min/1.73 m² is above the threshold of ≥20 mL/min/1.73 m² required for use 1.

Statin Therapy:

• Initiate moderate-to-high intensity statin for cardiovascular risk reduction, as CKD patients have 5-10 times higher cardiovascular mortality risk than progression to end-stage kidney disease 6, 3

Monitoring Frequency and Nephrology Referral

Monitoring Schedule for CKD Stage 3b:

• eGFR and UACR: Every 6 months if UACR <30 mg/g; every 3-4 months if UACR ≥30 mg/g 1, 6
• Hemoglobin: Every 6 months (twice yearly) 1
• Serum bicarbonate, potassium, calcium, phosphate: Every 3-6 months 1, 6
• PTH and vitamin D: Annually or as clinically indicated 1

Nephrology Referral Indications:

Refer to nephrology immediately if any of the following are present 1, 6, 3:

• eGFR <30 mL/min/1.73 m² (this patient is approaching this threshold at eGFR 37)
• Continuously increasing albuminuria despite optimal management
• Rapidly declining eGFR (>5 mL/min/1.73 m² per year)
• Difficulty managing CKD complications including resistant hypertension, refractory metabolic acidosis, or anemia
• Uncertainty about etiology or atypical features suggesting non-diabetic kidney disease (hematuria, rapid progression, absence of retinopathy in type 1 diabetes)

Common Pitfalls to Avoid

• Do not delay treatment of metabolic acidosis while waiting for repeat measurements, as serum bicarbonate of 15 mmol/L requires immediate intervention 4, 8, 5
• Do not discontinue ACE inhibitor/ARB for creatinine increases <30% in the absence of volume depletion, as this represents expected hemodynamic changes 1, 6
• Do not rely on serum creatinine alone—always calculate eGFR using validated equations (CKD-EPI 2021) and measure UACR 6, 2
• Do not skip albuminuria testing, as eGFR and UACR provide independent prognostic information for cardiovascular events, CKD progression, and mortality 1, 6, 2
• Do not initiate erythropoiesis-stimulating agents before correcting iron deficiency and excluding other reversible causes of anemia 1
• Do not overlook the leukocytosis with left shift—evaluate for infection or inflammatory process that may be contributing to acute-on-chronic kidney injury 3