What tests should be included in an initial blood workup (complete blood count, CBC)?

Initial Blood Work-Up: Complete Blood Count (CBC)

An initial blood work-up should include a complete blood count (CBC) with differential and platelets, along with a comprehensive metabolic panel, liver function tests, coagulation studies, and additional disease-specific markers based on clinical context.

Core Components of Initial Laboratory Assessment

Essential First-Line Tests

The foundational laboratory evaluation should include 1:

• Complete blood count (CBC) with differential and platelet count – provides critical information on red blood cells, white blood cells, and platelets 2, 3
• Comprehensive metabolic panel – includes electrolytes (sodium, potassium, chloride, bicarbonate, calcium, magnesium), renal function (blood urea nitrogen, creatinine), and glucose 1
• Liver function tests – ALT, AST, alkaline phosphatase, total bilirubin, albumin, and GGT 1, 4
• Urinalysis – essential screening test for renal and systemic disease 1

Additional Baseline Studies

Beyond the core CBC and chemistry panel, initial work-up should include 1:

• Lipid profile (fasting preferred) – for cardiovascular risk assessment 1
• Thyroid-stimulating hormone (TSH) – screens for thyroid dysfunction that can affect multiple organ systems 1
• Fasting blood glucose or glycohemoglobin (HbA1c) – for diabetes screening and metabolic assessment 1

Disease-Specific Considerations

When Hematologic Malignancy is Suspected

If acute lymphoblastic leukemia or other hematologic conditions are being evaluated, expand the work-up to include 1:

• Coagulation panel – D-dimer, fibrinogen, prothrombin time (PT), partial thromboplastin time (PTT) to assess for disseminated intravascular coagulation 1
• Tumor lysis syndrome panel – lactate dehydrogenase (LDH), uric acid, potassium, phosphate, and calcium 1
• Immunophenotyping – flow cytometry panel including CD19, CD20, CD5, CD10, CD11c, CD22, CD25, CD103, CD123 for lineage determination 1

When Liver Disease is Suspected

For patients with suspected hepatic pathology, the initial panel should include 1, 4:

• Bilirubin, albumin, ALT, alkaline phosphatase, and GGT – core liver assessment 1
• Full blood count if not performed within the previous 12 months 1
• AST – can be added reflexively to calculate AST:ALT ratio for fibrosis assessment (ratio >1 suggests advanced fibrosis/cirrhosis) 1
• Prothrombin time – assesses synthetic liver function 1

When Renal Malignancy is Being Evaluated

For kidney cancer work-up, laboratory assessment should include 1:

• CBC – baseline hematologic assessment 1
• Comprehensive metabolic panel – with specific attention to serum calcium, liver function studies, LDH, and creatinine 1
• Coagulation profile – PT/PTT assessment 1
• Urinalysis – essential for renal pathology 1

Clinical Context and Interpretation

Understanding CBC Components

The CBC provides multiple parameters with clinical significance 2, 3, 5:

• White blood cell count and differential – evaluates immune function and can indicate infection, inflammation, or hematologic malignancy 2, 3, 5
• Hemoglobin and hematocrit – assesses for anemia or polycythemia 2, 3
• Mean corpuscular volume (MCV) – helps classify anemia type 2, 3
• Red cell distribution width (RDW) – predicts cardiovascular disease and metabolic conditions 3
• Platelet count and indices – evaluates hemostatic function 2, 3
• Neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR) – emerging markers for cardiovascular and metabolic disease risk 3

Common Pitfalls to Avoid

Do not order liver transaminases (AST/ALT) together routinely on every initial panel – this approach lacks evidence support and increases false positives 1. Instead, order one transaminase initially (typically ALT), then add AST reflexively if abnormal to calculate the AST:ALT ratio 1.

Recognize that normal transaminases do not exclude cirrhosis – both AST and ALT can be within normal range even with advanced liver disease 1.

Consider that 10-20% of CBC results are reported as abnormal – not all abnormalities require immediate subspecialty referral 2. Structured algorithms help determine when consultation is necessary versus when primary care management is appropriate 2.

Risk-Based Testing

For high-risk populations (injection drug users, migrants from high-prevalence areas, prisoners), consider simultaneous second-line testing including 1:

• Hepatitis B surface antigen, hepatitis B core antibody, hepatitis C antibody 4
• Ferritin, iron levels, and transferrin saturation 4

Pregnancy testing should be performed in all female patients of childbearing age when treatment decisions may be affected 1.

Hepatitis B virus testing is recommended when immunotherapy or chemotherapy is being considered due to reactivation risk 1.