What blood tests are used to diagnose and manage congestive heart failure (CHF)?

Blood Tests for Congestive Heart Failure (CHF) Diagnosis and Management

Initial laboratory evaluation of patients with suspected CHF should include complete blood count, urinalysis, serum electrolytes (including calcium and magnesium), blood urea nitrogen, serum creatinine, fasting blood glucose (glycohemoglobin), lipid profile, liver function tests, thyroid-stimulating hormone, ferritin, and natriuretic peptides. 1

Essential Blood Tests for CHF Diagnosis

First-line Laboratory Tests (Class I recommendation)

• Complete blood count (CBC): To assess for anemia which can exacerbate or mimic heart failure
• Serum electrolytes: Including sodium, potassium, calcium, and magnesium
  • Hyponatremia may indicate severe heart failure
  • Electrolyte abnormalities may affect cardiac function and treatment safety
• Renal function tests: Blood urea nitrogen (BUN) and creatinine with estimated GFR
  • Essential for medication dosing and prognosis assessment
• Liver function tests: Bilirubin, AST, ALT, GGTP
  • May indicate hepatic congestion from right heart failure
• Fasting blood glucose and HbA1c: To identify diabetes as a comorbidity
• Thyroid-stimulating hormone (TSH): To rule out thyroid disorders that can cause or worsen heart failure
• Lipid profile: To assess cardiovascular risk factors

Biomarkers with Strong Diagnostic Value

• Natriuretic peptides (Class IIa recommendation):
  • B-type natriuretic peptide (BNP) or N-terminal pro-BNP (NT-proBNP)
  • Most powerful supplementary diagnostic test with net reclassification improvement of 69% 2
  • Particularly useful when echocardiography cannot be arranged promptly
  • Helps rule out heart failure when levels are normal (high negative predictive value)

Additional Tests Based on Clinical Suspicion

• Ferritin and transferrin saturation (TSAT): To assess for iron deficiency, which is common in heart failure
• Cardiac troponins: To rule out acute myocardial injury

Specialized Blood Tests for Specific Etiologies (Class IIa)

When clinically indicated, consider:

• Screening for hemochromatosis: Serum iron, ferritin, transferrin saturation
• Tests for rheumatologic diseases: ANA, rheumatoid factor
• Screening for amyloidosis: Serum and urine protein electrophoresis
• HIV testing: Especially in younger patients with unexplained cardiomyopathy
• Metanephrine measurements: If pheochromocytoma is suspected

Blood Tests for Monitoring CHF

• Electrolytes and renal function: Regularly monitor during treatment, especially when using diuretics, ACE inhibitors, or aldosterone antagonists
• Natriuretic peptides: Serial measurements may help guide therapy and assess response to treatment
• Liver function tests: To monitor hepatic congestion in right heart failure
• Complete blood count: To monitor for anemia which can worsen heart failure symptoms

Interpretation and Clinical Pitfalls

Important Considerations

• A normal ECG makes heart failure diagnosis unlikely (less than 10% probability) 3
• Laboratory tests should be interpreted in conjunction with clinical findings, ECG, and imaging studies
• Natriuretic peptides can be elevated in:
  • Advanced age
  • Renal dysfunction
  • Acute pulmonary embolism
  • Right ventricular strain

Common Pitfalls to Avoid

• Relying solely on laboratory tests without clinical correlation
• Failing to consider non-cardiac causes of elevated natriuretic peptides
• Not adjusting natriuretic peptide cutoff values for age, renal function, and obesity (which can lower values)
• Overlooking the need for regular monitoring of electrolytes and renal function during treatment

Algorithmic Approach to Laboratory Testing in CHF

1. Initial Presentation:

   • Order complete baseline panel (CBC, electrolytes, renal/liver function, glucose, lipids, TSH)
   • Measure natriuretic peptide levels (BNP or NT-proBNP)

2. If natriuretic peptides elevated:

   • Proceed to echocardiography
   • Order additional tests based on suspected etiology

3. If natriuretic peptides normal:

   • Heart failure is unlikely; consider alternative diagnoses
   • Exception: Obesity may cause falsely low values

4. During treatment:

   • Monitor electrolytes and renal function within 1-2 weeks of initiating or changing doses of ACE inhibitors, ARBs, or diuretics
   • Consider periodic natriuretic peptide measurements to assess treatment response

5. For worsening symptoms:

   • Repeat electrolytes, renal function, and natriuretic peptides
   • Consider additional tests based on clinical presentation

By following this systematic approach to laboratory testing, clinicians can effectively diagnose heart failure, identify underlying causes, and monitor treatment response while avoiding unnecessary testing.