What preoperative laboratory tests should be ordered for a patient with a history of diabetes, potential bleeding disorders, and anticoagulant medication use, such as warfarin (Coumadin) or aspirin, undergoing major foot surgery?

Preoperative Laboratory Testing for Major Foot Surgery

For a patient with diabetes, potential bleeding disorders, and anticoagulant use undergoing major foot surgery, order: PT/INR (for warfarin monitoring), hemoglobin/hematocrit, HbA1c (if diabetes is poorly controlled), and renal function tests (creatinine/BUN), with additional coagulation studies only if the bleeding history is abnormal. 1, 2

Coagulation Testing

Essential for anticoagulated patients:

• PT/INR is mandatory for patients on warfarin to verify INR <1.5 before surgery, as warfarin should be stopped 5-6 days preoperatively 2, 3
• Coagulation testing (PT, aPTT, platelet count) should be reserved for patients taking anticoagulants, those with liver disease or hematopoietic disorders, or patients with abnormal bleeding history (spontaneous bruising, excessive surgical bleeding, family history of coagulopathy) 1
• Indiscriminate preoperative coagulation testing is not warranted in patients without these risk factors 1
• For aspirin users, routine coagulation tests are not indicated as aspirin affects platelet function (not PT/aPTT), and bleeding history is more predictive than laboratory values 1

Critical pitfall: Routine coagulation panels detect only 2.1% abnormalities in unselected patients, and most abnormal results don't predict bleeding complications 4. Von Willebrand disease, the most common inherited coagulopathy, may show normal routine coagulation tests 1.

Hemoglobin/Hematocrit

• Obtain baseline hemoglobin/hematocrit to establish preoperative values and predict transfusion need, particularly important for major foot surgery with expected significant blood loss 2
• This allows for appropriate blood product availability planning 2

Glucose and HbA1c Testing

For diabetic patients:

• HbA1c is more useful than random glucose if results would change perioperative management 1
• Random glucose testing reflects only the past few hours and rarely alters perioperative management in known diabetics 1
• If HbA1c ≥8%, refer to endocrinology and delay elective surgery until improved to <8% (ideally <7%) 5
• Preoperative HbA1c should be measured for risk stratification in all diabetic patients 5

Important consideration: Careful perioperative glucose management affects surgical outcomes, but the incidence of occult diabetes in presurgical populations is only 0.5% 1.

Renal Function Testing (Electrolytes and Creatinine)

Indicated based on clinical factors, not age alone:

• Order BUN/creatinine for patients with hypertension, heart failure, chronic kidney disease, complicated diabetes, liver disease, or those taking diuretics, ACE inhibitors, ARBs, NSAIDs, or digoxin 1
• Renal function testing is particularly important for warfarin users, as warfarin effects may last several days depending on renal clearance 2
• Chronic kidney disease independently predicts abnormal postoperative creatinine (OR 3.1) and potassium (OR 1.8) requiring medical intervention 6

Avoid this pitfall: One guideline advocates testing in patients >40 years, but consensus favors history and physical examination findings over age alone 1

Tests NOT Routinely Indicated

Do not order routinely:

• Electrolyte panels in patients without the above risk factors - no trials document outcome changes from routine electrolyte testing 1
• Random glucose in well-controlled diabetics 1
• Coagulation panels (PT/aPTT/thrombin time/fibrinogen) in patients without bleeding history or anticoagulant use - only 8% of panel orders are clinically indicated, and 98% of fibrinogen results are normal 7
• Routine basic metabolic panels in patients with normal preoperative values and no major comorbidities contribute minimal actionable information 6

Anticoagulation-Specific Management

For warfarin users:

• Stop warfarin 5-6 days before surgery 2
• Verify INR <1.5 for most procedures 2
• Document bridging anticoagulation decision and reversal agent availability (vitamin K, prothrombin complex concentrate, FFP) 2

For clopidogrel users:

• Stop 7-10 days before elective surgery 2
• Consider special circumstances for coronary stents 2

Algorithm Summary

1. All patients: Hemoglobin/hematocrit 2
2. Warfarin users: PT/INR 2, 3
3. Diabetics: HbA1c if poorly controlled or if results would change management 1, 5
4. Patients with hypertension, heart failure, CKD, complicated diabetes, liver disease, or on specific medications: BUN/creatinine 1, 2
5. Abnormal bleeding history only: PT, aPTT, platelet count 1

Cost consideration: Routine unnecessary testing generates substantial hospital charges without improving outcomes - one study documented $472,372 in charges for tests that didn't contribute to actionable information 6.