Should I repeat the blood tests?

Approach to Repeat Blood Testing

Rather than simply repeating abnormal blood tests, you should determine the underlying cause unless there is high clinical suspicion that the abnormality is transient. 1

Decision Framework for Repeat Testing

When to Repeat Testing

• Transient conditions: Only repeat testing when there's high certainty that the abnormality will resolve in response to an identified acute insult 1
• Diagnostic confirmation: When confirming diabetes diagnosis, repeat testing is necessary unless there's a clear clinical diagnosis (e.g., hyperglycemic crisis or classic symptoms with random plasma glucose >200 mg/dL) 1
• Discordant results: If two different tests (e.g., A1C and FPG) show discordant results, the test above diagnostic threshold should be repeated 1
• Results near diagnostic thresholds: For results near diagnostic thresholds, follow-up and repeat testing in 3-6 months is recommended 1, 2

When NOT to Repeat Testing

• Chronic liver diseases: For conditions like HCV and NAFLD, even normalized liver blood tests don't necessarily imply absence or resolution of disease 1
• Already abnormal liver tests: Studies show 84% of abnormal liver tests remain abnormal after 1 month, and 75% remain abnormal after 2 years 1
• COVID-19 testing: For symptomatic or asymptomatic individuals with negative initial NAAT results, routine repeat testing is not recommended 1
• Routine critical value verification: Repeat testing of critical laboratory values (like hemoglobin, WBC, platelets, etc.) does not significantly improve accuracy 3

Test-Specific Considerations

Diabetes Testing

• If A1C is 7.0% and repeat result is 6.8%, diabetes diagnosis is confirmed 1
• Different tests have varying levels of preanalytic and analytic variability:
  • A1C: least variability
  • Fasting plasma glucose: moderate variability
  • 2-hour post-glucose challenge: highest variability 2

Liver Function Tests

• Instead of repeating abnormal liver tests, obtain a thorough clinical history and perform targeted examination to determine the cause 1
• Consider factors like:
  • Age, ethnicity, symptoms (jaundice, pain, weight loss)
  • Comorbidities, drug history, travel history
  • Alcohol consumption, metabolic syndrome features 1

COVID-19 Testing

• Single NAAT testing is generally sufficient 1
• Consider repeat testing only in specific situations:
  • Development of new/worsening symptoms without alternative explanations
  • Poorly collected specimen
  • If performed, repeat testing should occur 24-48 hours after initial testing 1

Potential Harms of Unnecessary Repeat Testing

• False positives: Overutilization carries risk of false positive results, triggering unnecessary investigations and costs 4
• Patient harm: Can cause iatrogenic anemia from repeated blood draws 4
• Resource waste: Repeat testing involves costs of recalling patients, obtaining and transporting samples, and laboratory analysis 1

Special Considerations

• Children: Lower threshold for referral to pediatrician for abnormal liver tests, as common adult causes are less common in children 1
• Critical values: For truly critical values indicating life-threatening conditions, prompt intervention is required rather than repeat testing 2
• Test reliability: Consider the inherent reliability and variability of specific tests when interpreting results 2

Remember that the extent of blood test abnormality is not necessarily a guide to clinical significance - this is determined by the specific analyte and clinical context 1. Focus on investigating the underlying cause rather than simply repeating the same tests.