What laboratory monitoring is required during maintenance therapy with Kessimpta (ofatumumab)?

Laboratory Monitoring for Kessimpta (Ofatumumab) During Maintenance Therapy

Kessimpta requires minimal routine laboratory monitoring during maintenance therapy, with the primary focus on immunoglobulin levels and hepatitis B screening—not the frequent CBC and liver function tests required by traditional immunosuppressants.

Pre-Treatment Mandatory Screening

Before initiating Kessimpta, two critical laboratory assessments are required:

• Hepatitis B virus (HBV) screening is mandatory before the first dose, as active HBV infection is an absolute contraindication to therapy 1
• Quantitative serum immunoglobulin levels (IgG and IgM) must be obtained at baseline to establish a reference point for future monitoring 1

Maintenance Laboratory Monitoring Requirements

Immunoglobulin Monitoring

The FDA label explicitly requires monitoring immunoglobulin levels at the beginning of treatment, during therapy, and after discontinuation until B-cell repletion occurs 1. This is the cornerstone of laboratory surveillance during maintenance therapy.

• Monitor IgM and IgG levels regularly throughout treatment, as low IgM increases the risk of infections with encapsulated bacteria 2
• Over 6 years of treatment data show that mean IgG levels remain stable, with 98.0% of patients maintaining IgG above the lower limit of normal (5.65 g/L) at all assessments 3
• Mean IgM levels decrease during therapy, but 64.1% of patients maintain IgM above the lower limit of normal (0.4 g/L) throughout treatment 3
• Consider discontinuing Kessimpta if a patient develops serious opportunistic infections or recurrent infections when immunoglobulin levels indicate immune compromise 1

B-Cell Monitoring

• CD19+ B-cell counts (not CD20, as ofatumumab interferes with CD20 assays) reach below the lower limit of normal in 95-99% of patients within 2 weeks of treatment initiation 1
• B-cell counts remain below the lower limit of normal in approximately 92-97% of patients from Week 12 through Week 120 while on continuous therapy 1
• Median time to B-cell recovery after treatment discontinuation is 24.6 weeks, with modeling predicting 23 weeks to reach the lower limit of normal 1

What Is NOT Required

Unlike traditional disease-modifying antirheumatic drugs that require frequent CBC and liver function test monitoring every 2-4 weeks initially, then every 8-12 weeks, Kessimpta does not require routine hematologic or hepatic laboratory monitoring 4. This represents a significant practical advantage over other immunosuppressive therapies.

• No routine CBC monitoring is mandated during maintenance therapy 4
• No routine liver function test monitoring is required 4
• No lipid monitoring is necessary, unlike JAK inhibitors which cause dose-dependent lipid elevations 5
• Ofatumumab does not carry warnings for hepatotoxicity, thrombocytopenia, cardiac toxicity, or QT prolongation 2

Infection Surveillance

• Delay Kessimpta administration in patients with active infection until the infection resolves 1
• The exposure-adjusted incidence rates of serious infections and malignancies do not increase over 6 years of continuous treatment 3
• Overall infection rates with ofatumumab (51.6%) are similar to those with teriflunomide (52.7%), and serious infection rates are comparable (2.5% vs. 1.8%) 6

Critical Clinical Pitfalls to Avoid

• Live-attenuated vaccines are absolutely contraindicated during ofatumumab treatment and after discontinuation until B-cell repletion occurs 2, 1
• All two-dose vaccine regimens should be completed at least 4-6 weeks before starting therapy 2
• Do not assume normal immunoglobulin levels persist indefinitely—regular monitoring is required to detect immune compromise before serious infections develop 1
• Switching from stable ofatumumab therapy risks disease reactivation during washout periods, as median B-cell recovery takes nearly 6 months 1

Practical Monitoring Algorithm

Baseline (before first dose):

• HBV screening (HBsAg, anti-HBc, anti-HBs) 1
• Quantitative IgG and IgM levels 1

During maintenance therapy:

• Immunoglobulin levels (IgG and IgM) at regular intervals—specific frequency not defined in FDA label but should be individualized based on infection history 1
• Clinical assessment for infections before each monthly dose 1

After discontinuation:

• Continue immunoglobulin monitoring until B-cell repletion (approximately 24-26 weeks post-treatment) 1