What preoperative lab tests are recommended for a patient undergoing major foot surgery, particularly for those with a history of diabetes, cardiovascular disease, or taking anticoagulant medications such as warfarin (coumarin) or aspirin (acetylsalicylic acid), and for patients over 50 years old?

Preoperative Laboratory Testing for Major Foot Surgery

For major foot surgery, obtain hemoglobin/hematocrit on all patients, PT/INR for warfarin users, HbA1c for diabetics (especially if poorly controlled), coagulation studies (PT/aPTT/platelets) for patients with bleeding history or on anticoagulants, and renal function tests (BUN/creatinine) for patients over 50 with cardiovascular disease, diabetes, hypertension, or taking specific medications. 1

Essential Testing for All Patients

Hemoglobin and Hematocrit should be obtained on all patients undergoing major foot surgery to establish baseline values and predict transfusion needs, particularly important when significant blood loss is expected 2, 1. The Network for Advancement of Transfusion Alternatives (NATA) guidelines recommend hemoglobin determination 28 days before elective orthopedic surgery when possible, with a target hemoglobin within the normal WHO range 2. Preoperative anemia (Hb <13 g/dL) occurs in 19-35% of orthopedic surgery patients and is associated with increased morbidity, mortality, and transfusion requirements 2.

Anticoagulation Management

Warfarin (Coumarin) Users

PT/INR testing is mandatory for all patients taking warfarin 2, 1. Warfarin must be discontinued 5-6 days before elective surgery, and INR should be verified <1.5 before proceeding 2, 1. The effects of warfarin may persist for several days depending on patient response and renal clearance 2. Vitamin K should be administered preoperatively for warfarin reversal to potentially avoid FFP transfusion 2.

Aspirin (Acetylsalicylic Acid) Users

Aspirin and other anticoagulation drugs should be discontinued before elective surgery, and surgery should be delayed until anticoagulation effects dissipate 2. For clopidogrel specifically, effects may last approximately one week 2.

Coagulation Panel Indications

Order PT, aPTT, and platelet count for patients with 1, 3:

• Current anticoagulant use
• Liver disease or hematopoietic disorders
• Abnormal bleeding history (spontaneous bruising, excessive surgical bleeding, family history of coagulopathy)

The American Academy of Family Physicians notes that routine coagulation panels detect only 2.1% abnormalities in unselected patients, and most abnormal results don't predict bleeding complications 1. A negative bleeding history eliminates the need for routine coagulation screening 3.

Diabetes-Specific Testing

HbA1c Testing

For diabetic patients, obtain HbA1c for risk stratification and perioperative management 2, 1, 4. HbA1c is more useful than random glucose if results would change perioperative management 1, 4.

If HbA1c ≥8%, refer to endocrinology and delay elective surgery until improved to <8% (ideally <7%) 1. Preoperative HbA1c should be measured in all diabetic patients undergoing major surgery 2, 1.

Cardiovascular Assessment in Diabetics

Diabetic patients require enhanced cardiovascular evaluation due to increased risk of silent myocardial ischemia and cardiac autonomic neuropathy 2. Question patients about:

• Atypical angina symptoms (dyspnea, exercise epigastric pain)
• Orthostatic or postprandial hypotension
• Episodes of serious unfelt hypoglycemia
• History of coronary, cerebrovascular, or peripheral vascular disease 2

ECG should be obtained if the last one was performed several months ago, searching for signs of ischemia, tachycardia, arrhythmia, or prolonged QTc interval 2.

Renal Function Testing

Order BUN and creatinine for patients with 1:

• Hypertension
• Heart failure
• Chronic kidney disease
• Complicated diabetes
• Liver disease
• Taking diuretics, ACE inhibitors, ARBs, NSAIDs, or digoxin

Renal function testing is particularly important for warfarin users, as warfarin effects depend on renal clearance 1. For patients with eGFR <45 mL/min/1.73 m², also check serum calcium, phosphate, PTH, and alkaline phosphatase to assess for metabolic bone disease 5.

Age-Related Considerations (Patients Over 50)

Patients over 50 years old have increased prevalence of undiagnosed conditions 2. The prevalence of anemia in elderly patients (>65 years) is 11% in men and 10.2% in women 2. For patients over 50 undergoing major foot surgery:

• Hemoglobin/hematocrit is essential 2, 1
• ECG if cardiovascular risk factors present or undergoing intermediate/high-risk surgery 5
• Renal function if hypertension, diabetes, or on relevant medications 1, 5
• Consider screening for undiagnosed diabetes if risk factors present 5

Testing NOT Routinely Recommended

Do not order routinely 5, 6:

• Chest radiography (only if new/unstable cardiopulmonary symptoms)
• Urinalysis (only for urologic procedures or prosthesis implantation)
• Electrolytes (only if specific risk factors present)
• Random glucose in non-diabetics (unless high risk for undiagnosed diabetes)

The American Society of Anesthesiologists found that routine testing identifies abnormalities in only 0.8-22% of cases, with changes in clinical management occurring in only 1.1-4% of abnormal results 5. Only order tests that would alter perioperative care 5, 6.

Common Pitfalls to Avoid

• Do not order coagulation studies without specific indications - they are poor predictors of bleeding (positive predictive value 0.03-0.22) in patients with negative bleeding history 3
• Do not delay surgery for mildly abnormal labs that don't affect management - focus on clinically significant abnormalities 6
• Do not skip anemia evaluation - preoperative anemia significantly impacts outcomes in orthopedic surgery and should be corrected when possible 2
• Do not forget to verify INR normalization in warfarin users before proceeding with surgery 2, 1