What labs should I order for a patient with suspected congestive heart failure (CHF) exacerbation?

Laboratory Tests for CHF Exacerbation

For a patient with suspected CHF exacerbation, order a comprehensive metabolic panel including electrolytes (sodium, potassium, calcium, magnesium), renal function tests (BUN, creatinine with eGFR), complete blood count, liver function tests (bilirubin, AST, ALT, GGT), glucose or HbA1c, TSH, and consider BNP or NT-proBNP to confirm the diagnosis and guide management. 1, 2

Core Laboratory Panel (Class I Recommendation)

The following tests are essential for initial assessment and should be ordered in all patients with suspected CHF exacerbation:

Renal Function and Electrolytes

• Serum electrolytes including sodium, potassium, calcium, and magnesium are critical because diuretic therapy (the mainstay of acute decompensation treatment) causes rapid shifts in these values, and abnormalities directly affect cardiac function and arrhythmia risk 1, 2
• BUN, creatinine, and estimated GFR are mandatory because renal dysfunction independently predicts mortality and cardiovascular outcomes in heart failure patients, with significantly increased risk when eGFR falls below 60 mL/min/1.73m² 1, 2, 3
• Serial monitoring of electrolytes and renal function is necessary when adjusting diuretic doses or medications affecting these parameters 2, 4

Hematologic Assessment

• Complete blood count with hemoglobin and white blood cell count identifies anemia (which worsens heart failure symptoms and prognosis) and infection as potential precipitants of decompensation 1, 2

Metabolic and Endocrine Evaluation

• Fasting blood glucose or glycohemoglobin (HbA1c) is necessary because diabetes is a major comorbidity that affects heart failure management and prognosis 1, 2
• Thyroid-stimulating hormone (TSH) must not be skipped—thyroid dysfunction is a reversible cause of heart failure that is easily missed and should be tested in all patients 1, 2

Hepatic Function

• Liver function tests (bilirubin, AST, ALT, GGT) detect hepatic congestion from right heart failure and guide medication safety monitoring 1, 2

Iron Studies

• Ferritin and transferrin saturation (TSAT) should be checked as iron deficiency is common in heart failure and affects prognosis 1

Natriuretic Peptide Testing (Class IIa Recommendation)

• BNP or NT-proBNP measurement is useful when clinical diagnosis is uncertain, helps establish disease severity, and guides prognosis 1, 2
• This is particularly valuable in the urgent care setting when differentiating heart failure from other causes of dyspnea 1, 2

Additional Testing in Selected Patients (Class IIa Recommendation)

Consider these tests when clinical suspicion exists based on presentation:

• Hemochromatosis screening in younger patients with unexplained cardiomyopathy 1, 2
• HIV testing in at-risk populations 1, 2
• Rheumatologic disease panels, amyloidosis workup, or pheochromocytoma screening when history and physical examination suggest these diagnoses 1, 2

Critical Pitfalls to Avoid

• Never omit calcium and magnesium from the electrolyte panel—these are specifically required by guidelines, not just sodium and potassium 1, 2
• Do not skip TSH testing even if the patient seems euthyroid clinically, as thyroid dysfunction is a reversible cause that significantly impacts outcomes 1, 2, 5
• Monitor renal function and electrolytes serially during acute management, particularly when titrating diuretics, as deteriorating renal function (eGFR <60 mL/min/1.73m²) independently predicts worse outcomes with hazard ratios of 1.54-1.86 for cardiovascular death or hospitalization 3, 4
• Assess for residual congestion as inadequate decongestion is associated with worse outcomes and readmission 4