What additional lab tests are recommended for a patient?

Additional Laboratory Tests for Patient Evaluation

The specific additional laboratory tests required depend entirely on the clinical context and suspected diagnosis, but several guidelines provide clear frameworks for common scenarios.

Iron Deficiency Anemia Workup

For patients with anemia, diagnose iron deficiency using a ferritin cutoff of <45 ng/mL rather than the traditional <15 ng/mL threshold 1. This higher threshold improves diagnostic accuracy, particularly in patients with underlying inflammation or chronic kidney disease where additional laboratory tests may be needed 1.

Essential Testing for IDA:

• Serum ferritin (cutoff <45 ng/mL) 1
• Complete blood count (CBC) 1
• Serum chemistry including creatinine 1
• H. pylori testing (non-invasive testing recommended if suspected) 1
• Celiac disease serology (initial test; small bowel biopsy only if serology positive) 1

Acute Severe Colitis Monitoring

For hospitalized patients with acute severe colitis, perform daily laboratory monitoring throughout the hospital stay 1:

Daily Required Tests:

• Full blood count (FBC) 1
• Urea and electrolytes (U&E) 1
• C-reactive protein (CRP) 1
• Liver function tests (baseline) 1
• Stool culture and Clostridium difficile testing (baseline) 1

Additional Baseline Screening:

• Hepatitis B and C serology 1
• HIV testing 1
• Varicella-zoster virus (VZV) status (if no history of chickenpox, shingles, or vaccination) 1
• Tuberculosis screening with interferon-gamma release assay 1

Fournier's Gangrene/Necrotizing Fasciitis

For suspected Fournier's gangrene with signs of systemic infection or sepsis, immediately obtain the following laboratory tests 1:

Essential Tests:

• Complete blood count 1
• Serum creatinine and electrolytes 1
• Inflammatory markers: C-reactive protein and procalcitonin 1
• Blood gas analysis 1
• Serum glucose, hemoglobin A1c, and urine ketones (to investigate undetected diabetes mellitus—this is a strong recommendation) 1

Risk Stratification Scores:

• Laboratory Risk Indicator for Necrotising Fasciitis (LRINEC) score for early diagnosis 1
• Fournier's Gangrene Severity Index (FGSI) for prognosis 1

Community-Acquired Pneumonia (Hospitalized Patients)

For admitted patients with community-acquired pneumonia, obtain the following tests rapidly without delaying initial empiric therapy 1:

Required Laboratory Tests:

• Complete blood count with differential 1
• Blood chemistry: glucose, serum sodium, liver and renal function tests, electrolytes 1
• Oxygen saturation by oximetry (all patients) 1
• Arterial blood gas (for severe illness or chronic lung disease patients to assess oxygenation and CO2 retention) 1
• Two sets of blood cultures (before antibiotic initiation; yield approximately 11%) 1

Optional Tests:

• Sputum Gram stain and culture (if drug-resistant pathogen or unusual organism suspected; collect before antibiotics) 1

Alzheimer's Disease and Dementia Evaluation

When diagnostic uncertainty remains after initial evaluation, obtain additional (Tier 2-4) laboratory tests guided by the patient's individual medical, neuropsychiatric, and risk profile 1. Use a deliberate, personalized approach rather than broad-based "shotgun" testing 1.

Tier 2 Tests (Primary Clinicians May Consider):

Based on clinical characteristics and risk profile 1

Tier 3-4 Tests (Specialist Guidance):

Reserved for atypical, rare, or rapidly progressive conditions with continued diagnostic uncertainty 1

Multiple Myeloma Surveillance

For smoldering myeloma patients under observation, perform surveillance tests at 3-6 month intervals 1:

Blood Tests:

• CBC 1
• Serum chemistry: creatinine, albumin, LDH, calcium, β2-microglobulin 1
• Serum quantitative immunoglobulins, SPEP, and SIFE 1
• Serum free light chain (FLC) assay 1

Urine Tests:

• 24-hour urine assay for total protein, UPEP, and UIFE 1

Key Principles for Additional Testing

Avoid routine broad-based testing; instead, use clinical judgment to select tests based on specific diagnostic uncertainty 1. The goal is to answer specific clinical questions rather than perform exhaustive screening 2.

For patients on anticoagulation (warfarin), perform periodic PT/INR determination, with additional testing immediately after hospital discharge and whenever medications (including botanicals) are initiated, discontinued, or taken irregularly 3.