What laboratory tests should be ordered before referring a patient to nephrology?

Laboratory Tests to Order Before Nephrology Referral

Essential Basic Laboratory Panel

Before referring any patient to nephrology, order a comprehensive metabolic panel that includes serum creatinine with calculated eGFR, blood urea nitrogen (BUN), electrolytes (sodium, potassium, chloride, bicarbonate), calcium, and liver function tests. 1, 2

Core Kidney Function Tests

• Serum creatinine and eGFR are mandatory to stage CKD and determine urgency of referral 1, 2
• Urinalysis with microscopy to detect hematuria, pyuria, casts, and crystals 1, 2
• Urine albumin-to-creatinine ratio (UACR) or protein-to-creatinine ratio (PCR) from a spot urine sample to quantify proteinuria 1, 2
  • Two of three specimens collected within 3-6 months should be abnormal to confirm persistent albuminuria 1

Complete Blood Count and Additional Tests

• CBC to assess for anemia of chronic kidney disease 1
• Serum calcium, phosphorus, and alkaline phosphatase to evaluate for CKD mineral and bone disorder 1
• Lactate dehydrogenase (LDH) may be included at physician discretion 1

Electrolyte Assessment

• Serum potassium is critical as persistent hyperkalemia is itself an indication for nephrology referral 2
• Serum bicarbonate to assess for metabolic acidosis 1

Timing and Interpretation Considerations

Establish Baseline and Trend

• Obtain at least two eGFR measurements 3-6 months apart to calculate rate of decline and distinguish acute from chronic kidney disease 2
• A rapid decline >5 mL/min/1.73 m² per year or abrupt sustained decrease >20% warrants urgent referral 2

Proteinuria Quantification

• Persistent proteinuria >1 g/day (ACR ≥60 mg/mmol or PCR ≥100 mg/mmol) is an absolute indication for nephrology referral regardless of eGFR 2
• Normal to mildly increased albuminuria (<30 mg/g, category A1) does not require specialist input if eGFR is stable 1, 2

Special Populations

Diabetic Patients

• Hemoglobin A1c to assess glycemic control 1
• Lipid panel as cardiovascular risk is the primary concern in early CKD 1
• Absence of diabetic retinopathy with significant proteinuria suggests non-diabetic kidney disease and warrants referral 2

Patients with Hematuria

• Urine microscopy showing >20 RBCs per high-power field or red blood cell casts requires nephrology evaluation 2
• Consider urine cytology if central renal mass suggests urothelial carcinoma 1

Common Pitfalls to Avoid

• Do not refer based on a single elevated creatinine without confirming it is sustained and excluding reversible causes like volume depletion, medication effects, or obstruction 2
• Do not order a bone scan or brain imaging unless the patient has specific symptoms (bone pain, elevated alkaline phosphatase, neurological signs) 1
• Do not delay obtaining urine albumin quantification - dipstick protein alone is insufficient for staging and risk stratification 1, 2
• Do not fail to adjust medication dosages based on eGFR before referral, as this is a primary care responsibility 1, 2

When These Labs Indicate Referral

Refer immediately if labs show: 2, 3

• eGFR <30 mL/min/1.73 m²
• Proteinuria >1 g/day
• Rapid eGFR decline >5 mL/min/1.73 m² per year
• Persistent hyperkalemia despite treatment
• Urinary RBC casts or >20 RBCs/HPF without clear explanation

Consider referral for diabetic patients with: 1, 2

• eGFR <60 mL/min/1.73 m² plus difficult-to-control hypertension or electrolyte abnormalities
• Continuously increasing albuminuria despite optimal treatment
• Absence of retinopathy with significant proteinuria (suggests non-diabetic kidney disease)