What labs are recommended for patients undergoing gastric bypass surgery?

Recommended Laboratory Tests for Gastric Bypass Surgery

Before undergoing gastric bypass surgery, patients should have comprehensive laboratory testing to assess nutritional status, identify deficiencies, and evaluate comorbidities. 1

Essential Preoperative Laboratory Tests

• Complete blood count (CBC) to evaluate for anemia and assess platelet count 1
• Ferritin, folate, and vitamin B12 levels to screen for hematologic deficiencies 1
• Serum 25-hydroxyvitamin D levels to assess vitamin D status 1
• Serum calcium levels to establish baseline 1
• Parathyroid hormone (PTH) levels to screen for hyperparathyroidism 1
• Coagulation studies including prothrombin time, partial thromboplastin time, and INR for patients undergoing percutaneous procedures 1
• Liver function tests to assess for non-alcoholic fatty liver disease (NAFLD) 1
• Renal function tests to establish baseline kidney function 1
• HbA1c to screen for diabetes 1
• Lipid profile to assess cardiovascular risk 1

Additional Tests for Malabsorptive Procedures

For patients undergoing more extensive malabsorptive procedures such as biliopancreatic diversion with duodenal switch (BPD/DS):

• Serum vitamin A levels 1
• Serum zinc levels 1
• Serum copper levels 1
• Serum selenium levels 1

Discretionary Tests Based on Clinical Indication

• Arterial blood gas analysis if there are concerns about respiratory compromise 1
• Thiamine levels if there is suspicion of deficiency 1
• Magnesium levels if clinically indicated 1

Postoperative Laboratory Monitoring

Regular monitoring is essential after gastric bypass surgery:

• Complete blood count, ferritin, folate, and vitamin B12 levels at regular intervals 1
• Calcium, vitamin D, and PTH levels to monitor bone health 1
• Liver and kidney function tests 1
• HbA1c for patients with preoperative diabetes 1
• Lipid profile for patients with preoperative dyslipidemia 1

For patients who have undergone Roux-en-Y gastric bypass (RYGB), additional monitoring should include:

• Zinc levels 1
• Copper levels 1
• Selenium levels 1

Timing of Postoperative Monitoring

• Initial follow-up laboratory tests at 6 months post-surgery 1
• Subsequent testing at 1 year post-surgery 1
• Annual testing thereafter 1

Clinical Considerations

• Nutritional deficiencies are common in patients with obesity even before surgery, with vitamin D deficiency reported in up to 99% of patients 1
• Iron deficiency and anemia are prevalent in 0-47% of patients preoperatively 1
• Folate deficiency ranges from 0-63% preoperatively 1
• Vitamin B12 deficiency ranges from 0-23% preoperatively 1
• Preoperative deficiencies should be corrected before surgery as patients have an increased risk of worsening deficiencies postoperatively 1

Common Pitfalls to Avoid

• Failing to check vitamin B12 levels when prescribing high-dose folic acid, as folic acid can mask B12 deficiency 1
• Overlooking the need for more frequent monitoring in patients with malabsorptive procedures 1
• Not checking zinc and copper simultaneously, as supplementation of one can affect levels of the other 1
• Relying solely on vitamin B12 levels to diagnose deficiency, as methodological problems can affect sensitivity and specificity 1
• Neglecting to monitor patients long-term, as some deficiencies may develop years after surgery 1

By following these laboratory testing recommendations, clinicians can help minimize complications and optimize outcomes for patients undergoing gastric bypass surgery.