What initial lab tests are recommended for a patient evaluation, such as Complete Blood Count (CBC), Comprehensive Metabolic Panel (CMP), Liver Function Tests (LFTs), Prothrombin Time (PT), International Normalized Ratio (INR), and Partial Thromboplastin Time (PTT)?

Initial Laboratory Testing Panel

For a comprehensive initial patient evaluation, order: CBC with platelets and peripheral smear, comprehensive metabolic panel (including electrolytes and renal function), liver function tests (bilirubin, albumin, ALT, ALP, GGT), PT/INR, aPTT, and fibrinogen level. 1, 2, 3

Core Laboratory Tests

Complete Blood Count (CBC)

• CBC with platelet count and peripheral blood smear is essential for evaluating thrombocytopenia, anemia from chronic blood loss, and abnormal platelet morphology 2, 3
• The peripheral smear provides critical information about cell morphology that automated counts cannot detect 2

Comprehensive Metabolic Panel (CMP)

• Blood glucose, electrolytes, and renal function tests (BUN, creatinine) should be obtained routinely, as hypoglycemia can mimic other acute conditions and electrolyte abnormalities influence treatment decisions 1
• These tests identify systemic conditions that may cause or complicate the clinical presentation 1

Liver Function Tests (LFTs)

• Initial liver assessment should include bilirubin, albumin, ALT, ALP, and GGT 1
• This panel provides high sensitivity for detecting liver disease without generating excessive false positives 1
• AST can be added reflexively to calculate the AST:ALT ratio if initial tests are abnormal, as a ratio >1 indicates advanced fibrosis/cirrhosis even when both values are within normal range 1

Coagulation Studies

Prothrombin Time and INR

• PT/INR assesses the extrinsic coagulation pathway (factors II, V, VII, X) and is critical before any invasive procedures or when bleeding is present 1, 2, 3
• PT/INR is particularly important for patients on warfarin or with suspected liver dysfunction 1

Activated Partial Thromboplastin Time (aPTT)

• aPTT evaluates the intrinsic coagulation pathway (factors VIII, IX, XI, XII) and detects heparin effect 1, 2, 3
• Both PT and aPTT should be obtained, though therapy should not be delayed waiting for results unless there is clinical suspicion of bleeding abnormality, recent anticoagulant use, or uncertain medication history 1

Fibrinogen Level

• Fibrinogen level (Clauss method) should be included as part of first-line coagulation assessment 2, 3
• This is particularly important for detecting fibrinogen disorders that may not be apparent on PT/aPTT alone 2

Critical Timing Considerations

• Do not delay urgent treatment waiting for coagulation results unless there is specific clinical suspicion of bleeding abnormality, known anticoagulant use, or uncertain medication history 1
• For acute stroke evaluation, thrombolytic therapy should proceed while awaiting PT/aPTT/platelet results unless the three conditions above are present 1

Important Caveats

• Normal PT and aPTT do not rule out all coagulation disorders, as patients can have significant bleeding disorders with normal screening tests 4, 3
• Single measurements are insufficient in evolving clinical situations; serial monitoring may be necessary 3
• For eating disorder evaluation, this same panel (CBC, CMP, liver enzymes) is specifically recommended to identify medical complications 1

Context-Specific Additions

If Bleeding History Present:

• Add von Willebrand factor testing (VWF:Ag, VWF:RCo, Factor VIII) to first-line panel 2, 3
• Include ABO blood group, as type O patients have 25-60% lower VWF levels 2, 3

If Liver Disease Suspected:

• Ensure hepatic function tests are complete, including consideration of PT/INR as a marker of synthetic function 1
• Note that INR is unreliable in liver failure and activity percentage expression should be used instead 5

If Cardiac Concerns:

• Add cardiac enzymes and obtain 12-lead ECG, as cardiac abnormalities are prevalent and acute cardiac conditions may require urgent treatment 1