What labs to order for a patient with retroperitoneal liposarcoma on Verzenio (abemaciclib) presenting with bloody diarrhea, without abdominal pain, fever, or other symptoms?

Laboratory Workup for Bloody Diarrhea in Cancer Patient on Verzenio

Order a complete blood count with differential, comprehensive metabolic panel, inflammatory markers (CRP, procalcitonin), coagulation studies, and stool studies including C. difficile testing and bacterial pathogens. 1

Essential Blood Tests

The ESMO guidelines provide a comprehensive framework for laboratory evaluation in cancer patients with diarrhea, which should be obtained immediately in this patient with bloody diarrhea on abemaciclib:

Hematologic and Chemistry Panel

• Complete blood count with differential to assess for:

  • Neutropenia (abemaciclib causes neutropenia in 80% of patients) 2
  • Anemia from blood loss (hemoglobin decreased in 82% on Verzenio) 2
  • Leukocytosis suggesting infection 1
  • Thrombocytopenia (occurs in 36% on Verzenio) 2

• Comprehensive metabolic panel including:

  • Electrolytes (potassium, sodium, calcium, magnesium) to assess dehydration and guide fluid replacement 1
  • Creatinine and BUN for renal function (abemaciclib increases creatinine through tubular secretion inhibition, not true renal impairment) 2
  • Liver function tests (ALT/AST) as abemaciclib causes transaminitis in 48% and 37% respectively 2

Inflammatory and Infection Markers

• C-reactive protein (CRP) and procalcitonin to assess for infection and inflammation severity 1
• Coagulation studies to evaluate bleeding risk, particularly given the bloody diarrhea 1

Stool Studies

Critical stool testing should include:

• C. difficile testing using a two-step approach (glutamate dehydrogenase EIA plus toxin detection or nucleic acid amplification) 1

  • This is particularly important as cancer patients have higher infection rates due to immunosuppression 1
  • C. difficile can present with bloody diarrhea and is common in cancer patients 1

• Bacterial stool culture for Shigella, Salmonella, Campylobacter, and Shiga toxin-producing E. coli (STEC) O157:H7 1

• Parasitic examination for Giardia lamblia, Cryptosporidium, and Entamoeba histolytica 1

Clinical Context and Pitfalls

Abemaciclib-specific considerations: Diarrhea occurs in 81% of patients on Verzenio plus endocrine therapy, with grade 3 diarrhea in 9% 2. However, the presence of blood in the stool is NOT a typical feature of abemaciclib-induced diarrhea and warrants investigation for alternative etiologies including infection, ischemia, or tumor-related bleeding.

Key pitfall: The creatinine elevation seen with abemaciclib (98% of patients) is due to inhibition of renal tubular secretion transporters, not true renal dysfunction 2. Consider alternative markers like BUN or cystatin C if concerned about actual renal impairment 2.

When to expand workup: If the patient develops fever, worsening symptoms, or laboratory evidence of severe inflammation (CRP >100, leukocytosis >15,000), consider blood cultures (minimum two sets including from any indwelling catheters) and imaging to evaluate for complications like colitis or perforation 1.

The absence of fever and abdominal pain does not exclude serious pathology—bloody diarrhea in an immunocompromised cancer patient requires thorough infectious and inflammatory workup regardless of symptom severity 1.