What lab tests are recommended pre and post Rituxan (rituximab) infusion?

Laboratory Testing for Rituximab (Rituxan) Infusion

Pre-Infusion Laboratory Testing

Before initiating rituximab therapy, obtain hepatitis B screening (HBsAg and anti-HBc), hepatitis C antibodies, complete blood count with differential and platelets, and baseline immunoglobulin levels (IgG, IgA, IgM). 1, 2, 3

Mandatory Pre-Treatment Screening

• Hepatitis B virus screening is required before the first infusion, measuring both hepatitis B surface antigen (HBsAg) and hepatitis B core antibody (anti-HBc) to detect occult infection 1, 2, 3
• Hepatitis C antibody screening should be performed before treatment initiation 1, 2
• Complete blood count (CBC) with differential and platelet count must be obtained prior to the first dose 1, 3
• Baseline immunoglobulin levels (IgG, IgA, IgM) should be measured, as pre-existing hypogammaglobulinemia (IgG <6 g/L) predicts increased risk of severe hypogammaglobulinemia and serious infections after rituximab 1
• Latent tuberculosis screening is recommended before initiating therapy 1

Critical Pre-Treatment Considerations

A common pitfall is failing to screen for hepatitis B core antibody in addition to surface antigen—both are required because occult hepatitis B can reactivate with fatal consequences. 1, 3

• Patients who are hepatitis B core antibody positive require prophylactic antiviral therapy (not just monitoring) when initiating rituximab, regardless of surface antigen status 1
• Pre-existing hypogammaglobulinemia (IgG <3 g/L) predicts greater risk of secondary immunodeficiency with rituximab treatment 1

During Treatment Monitoring

For Lymphoid Malignancies

• During rituximab monotherapy: Obtain CBC with differential and platelet counts prior to each rituximab course 3
• During rituximab plus chemotherapy: Obtain CBC with differential and platelet counts at weekly to monthly intervals, with more frequent monitoring in patients who develop cytopenias 3

For Autoimmune Conditions (RA, GPA, MPA)

• Obtain CBC with differential and platelet counts at 2-4 month intervals during rituximab therapy 1, 2, 3
• Continue monitoring for cytopenias after the final dose until resolution 3

Monitoring for Myelosuppression

Monitor for myelosuppression throughout treatment, as this is a key toxicity requiring dose adjustments or treatment delays. 4

• Antibiotic prophylaxis for shingles and pneumocystis is recommended when rituximab is combined with purine analog-based therapy 4
• For alemtuzumab-containing regimens, monitor for CMV reactivation 4

Post-Infusion Monitoring

Immediate Post-Infusion (First 24 Hours)

Infusion reactions occur in up to 77% of patients during their first rituximab exposure, with most reactions occurring within 3 hours of infusion initiation. 4, 1, 5, 6

• The risk of infusion reactions paradoxically decreases with subsequent infusions 4
• Respiratory symptoms are the most common type of infusion reaction (66% of all events) 6
• Most reactions are mild to moderate (grade 1-2), with only 18% requiring medical intervention 6
• Severe infusion reactions (bronchospasm, hypotension) occur in approximately 10% of patients 7

Laboratory Changes During Infusion Reactions

Two distinct mechanisms cause rituximab infusion reactions: mast cell-mediated hypersensitivity and cytokine release syndrome—distinguishing between them guides management. 4

Mast Cell-Mediated Reactions

• No change in CBC with differential 4
• Elevated serum tryptase 4
• Clinical features: urticaria, angioedema, wheezing, hypotension 4

Cytokine Release Syndrome

• Decreased cell counts on CBC 4
• Elevated creatinine, ESR, CRP, LDH, uric acid 4
• Decreased potassium and calcium 4
• Elevated IL-6 4
• Clinical features: fever >38.4°C, rigors, chills 4

Long-Term Monitoring (Weeks to Months)

• B-cell depletion begins within 3 days of rituximab administration but clinical improvement typically becomes evident between 6-11 weeks after treatment initiation 8
• Circulating B cells remain depleted for 6-12 months in most patients, with recovery beginning at approximately 6 months and median B-cell levels returning to normal by 12 months 2, 8
• Unexpected T cell depletion (mainly CD4+ cells) occurs in most patients, with CD4+ counts decreasing by a mean of 37% at week 12; lack of CD4+ depletion is associated with poor clinical response 9
• CD4+ cell counts can fall below 200 cells/μL in some patients, requiring monitoring for opportunistic infections 9

Post-Treatment Surveillance

• Continue monitoring CBC for cytopenias after the final dose until resolution 3
• Monitor for infectious complications, as B-cell depletion may persist for more than 8-12 months 8
• Remain vigilant for progressive multifocal leukoencephalopathy, a rare but fatal complication 1, 2