What initial tests should be ordered in primary care?

Initial Tests to Order in Primary Care

In primary care, the recommended initial laboratory tests for all patients include a complete blood count (CBC), comprehensive metabolic panel, lipid profile, thyroid-stimulating hormone (TSH), urinalysis, and appropriate age/risk-based screening tests. 1

Core Laboratory Testing

Basic Laboratory Panel

• Complete Blood Count (CBC) with differential: Evaluates for anemia, infection, and hematologic disorders
• Comprehensive Metabolic Panel: Includes:
  • Renal function: Blood urea nitrogen (BUN), creatinine with estimated GFR
  • Electrolytes: Sodium, potassium, chloride, calcium, magnesium, phosphate
  • Hepatic function: ALT, AST, alkaline phosphatase, bilirubin
  • Glucose and albumin
• Lipid Profile: Total cholesterol, LDL-C, HDL-C, triglycerides 1, 2
• Thyroid-Stimulating Hormone (TSH): At least once for all patients 1

Additional Basic Testing

• Urinalysis: Though routine screening urinalysis has limited value in asymptomatic patients 3, it remains recommended in the initial evaluation of patients with specific symptoms or conditions
• C-reactive protein (CRP) and Erythrocyte Sedimentation Rate (ESR): For inflammatory markers when clinically indicated 1

Age and Risk-Based Testing

Cardiovascular Risk Assessment

• Fasting Plasma Glucose or HbA1c: For diabetes screening and monitoring 1
• Lipoprotein(a): One-time measurement for cardiovascular risk assessment 2

Women's Health

• Cervical Cytology: As indicated by age-appropriate screening guidelines 1
• Pregnancy Testing: When relevant to symptoms or treatment decisions

Infectious Disease Screening

• HIV, Hepatitis B, Hepatitis C: Based on risk factors and age-appropriate screening recommendations
• Sexually Transmitted Infection Testing: Gonorrhea, chlamydia, syphilis based on risk factors 1

Special Considerations

Cognitive Concerns

For patients with cognitive or behavioral symptoms, a multi-tiered approach is recommended:

• Tier 1 "Cognitive Lab Panel": CBC, comprehensive metabolic panel, TSH, vitamin B12, homocysteine, CRP, and ESR 1
• Structural Brain Imaging: MRI preferred, or CT if MRI is contraindicated 1

Preconception Care

For women planning pregnancy:

• Blood Type and Screen
• Rubella Immunity Status
• Vitamin B12 Levels
• Additional Testing: Based on risk factors and ethnic background 1

Point-of-Care Testing Benefits

Point-of-care testing for comprehensive metabolic panels can reduce waiting times and improve efficiency in urgent situations, with studies showing a median reduction of 22 minutes in emergency department length of stay 4.

Common Pitfalls to Avoid

1. Overordering Tests: Routine screening tests without clinical indication have limited value and may lead to unnecessary follow-up testing 3, 5

2. Underordering Critical Tests: Missing key tests like lipid profiles or diabetes screening can delay identification of modifiable cardiovascular risk factors

3. Misinterpreting Results: Laboratory values should be interpreted in clinical context rather than in isolation 1

4. Failing to Follow Up: Establishing a reliable system for test result follow-up is essential to prevent missed diagnoses

5. Not Considering Cost: The financial impact of testing should be considered, especially for uninsured patients

By following these evidence-based recommendations for initial testing in primary care, clinicians can efficiently screen for common conditions while avoiding unnecessary testing, ultimately improving patient outcomes through early detection and intervention.