What is the appropriate management for a 65-year-old male with macrocytic anemia, positive dengue and typhoid IgM, and a peripheral blood smear showing macrocytes, target cells, and tear-drop cells?

Management of Macrocytic Anemia with Concurrent Dengue and Typhoid Infection

This patient requires immediate evaluation for vitamin B12 deficiency with serum B12 and methylmalonic acid levels, while providing supportive care for concurrent dengue and typhoid infections. 1, 2

Primary Diagnostic Consideration: Megaloblastic Anemia

The markedly elevated MCV of 116 fL with macrocytes on peripheral blood smear strongly suggests megaloblastic anemia, most likely from vitamin B12 or folate deficiency. 1, 2

• The presence of macrocytes, target cells, and tear drop cells on PBS indicates a megaloblastic process requiring urgent investigation. 2
• At age 65, vitamin B12 deficiency from pernicious anemia or malabsorption is the most probable etiology. 1
• The hemoglobin of 13.6 g/dL represents mild anemia, but the low RBC count (3.4 million) with high MCV confirms true macrocytosis rather than reticulocytosis. 2

Immediate Diagnostic Workup

Order the following tests immediately:

• Serum vitamin B12 level (most critical test). 1, 2
• Serum folate level. 1, 2
• Methylmalonic acid and homocysteine if B12 is borderline (200-400 pg/mL). 2
• Reticulocyte count to assess bone marrow response. 2
• Peripheral smear review for macro-ovalocytes and hypersegmented neutrophils (>5 lobes), which confirm megaloblastic anemia. 2
• Thyroid function tests and liver function tests to exclude nonmegaloblastic causes. 1, 2

Management of Vitamin B12 Deficiency

If B12 deficiency is confirmed, initiate parenteral vitamin B12 immediately:

• Administer 100 mcg intramuscular or deep subcutaneous injection daily for 6-7 days. 3
• Continue with 100 mcg on alternate days for seven doses, then every 3-4 days for 2-3 weeks. 3
• Maintenance therapy is 100 mcg monthly for life. 3
• Avoid intravenous administration as almost all vitamin will be lost in urine. 3
• Administer folic acid concomitantly if folate deficiency is also present. 3

Management of Concurrent Infections

Dengue Fever Management

Provide supportive care as dengue treatment is entirely symptomatic:

• Manage as outpatient with daily complete blood count monitoring unless warning signs develop. 4, 5
• Ensure adequate hydration with oral fluids. 5
• Use acetaminophen for fever and myalgias; avoid aspirin and NSAIDs due to hemorrhage risk. 4, 5
• Monitor for warning signs of severe dengue: abdominal pain, persistent vomiting, mucosal bleeding, lethargy, hepatomegaly, or rising hematocrit with falling platelets. 5
• Dengue IgM positivity indicates infection within recent months, as IgM can persist for >60 days after acute illness. 4

Typhoid Fever Management

Initiate empirical antibiotic therapy for typhoid fever:

• Start ceftriaxone if the patient appears clinically unstable. 4
• If clinically stable and traveled from areas with preserved ciprofloxacin sensitivity, ciprofloxacin is an alternative. 4
• Treat for 2 weeks total duration. 4
• Blood cultures should be obtained before antibiotics if not already done, as they are 80% sensitive in the first week. 4

Critical Monitoring Parameters

Daily monitoring should include:

• Complete blood count to track hemoglobin, platelet count, and hematocrit for dengue complications. 5
• Clinical assessment for dengue warning signs (critical phase typically occurs days 3-7 of illness). 5
• Response to vitamin B12 therapy: expect reticulocytosis within 3-7 days and hemoglobin improvement within 2-3 weeks. 3
• Temperature curve and clinical response to typhoid treatment. 4

Important Caveats

• The macrocytic anemia is unlikely to be caused by dengue or typhoid infections themselves; these are coincidental findings requiring separate management. 1, 2
• If the patient develops thrombocytopenia, leukopenia, or worsening anemia beyond baseline, consider malaria as a differential diagnosis despite negative initial testing, as three thick and thin films over 72 hours are required to exclude malaria with confidence. 6, 7
• Myelodysplastic syndrome remains a differential diagnosis in this 65-year-old with macrocytosis; if B12/folate levels are normal and no other cause is identified, hematology referral for bone marrow evaluation is warranted. 1
• Do not delay B12 replacement while awaiting test results if clinical suspicion is high, as neurologic complications can develop and may be irreversible. 1