How can you determine if a patient is adhering to their hydroxyurea regimen?

Assessing Hydroxyurea Adherence in Patients

Adherence to hydroxyurea therapy should be assessed through a combination of laboratory monitoring, specifically mean corpuscular volume (MCV), hemoglobin F (HbF) levels, and complete blood count parameters, along with direct patient interviews about medication use. 1

Laboratory Parameters to Monitor Adherence

Primary Laboratory Indicators

• Mean Corpuscular Volume (MCV):

  • An increased MCV is a reliable marker of hydroxyurea adherence
  • 75.3% of providers use this parameter to assess adherence 2
  • Look for elevation from baseline as a sign of good adherence

• Hemoglobin F (HbF) levels:

  • Elevated HbF indicates good adherence to hydroxyurea
  • 70.7% of providers use HbF levels to monitor adherence 2
  • Typically increases within 3-6 months of consistent therapy

Complete Blood Count Parameters

• Neutrophil count: Moderate neutropenia may indicate adherence
• Platelet count: Mild thrombocytopenia may indicate adherence
• Reticulocyte count: Decreased counts suggest adherence

Clinical Response Assessment

Hematologic Response

• Complete response is defined as 1:

  • Hematocrit less than 45% without phlebotomy
  • Platelet count < 400 × 10^9/L
  • WBC count < 10 × 10^9/L
  • No disease-related symptoms

• Partial response is defined as 1:

  • Hematocrit less than 45% without phlebotomy
  • Response in three or more of the other criteria

Monitoring Schedule

• Most providers (64.7%) follow laboratory values monthly 2
• Nearly half (41.9%) see patients monthly for clinical assessment 2
• Consistent monitoring allows for detection of adherence patterns

Direct Assessment Methods

• Patient interviews: 84.2% of providers use this method 2

  • Ask specific questions about:
    • Missed doses in the past week
    • Barriers to taking medication
    • Side effects experienced

• Medication refill history:

  • Check pharmacy records for timely refills
  • Calculate medication possession ratio

Signs of Non-Adherence

Laboratory Indicators

• Failure to achieve expected laboratory changes:
  • No increase in MCV
  • No elevation in HbF levels
  • No expected mild myelosuppression

Clinical Indicators

• Persistent disease manifestations despite adequate prescribed dosing:
  • For PV: Need for frequent phlebotomy to keep hematocrit < 45% 1
  • Uncontrolled myeloproliferation (platelet count > 400 × 10^9/L AND WBC > 10 × 10^9/L) 1
  • Failure to reduce splenomegaly or relieve splenomegaly-related symptoms 1

Common Barriers to Adherence

Understanding barriers can help identify non-adherence:

Unintentional Non-Adherence (70% of cases) 3

• Forgetfulness: Most common reason for missed doses
• External factors: Work schedules, travel, lack of access

Intentional Non-Adherence (30% of cases) 3

• Negative perceptions of hydroxyurea
• Fear of side effects
• Aversion to taking medications in general

Pitfalls in Assessing Adherence

• Relying solely on patient self-report: May overestimate adherence
• Assuming laboratory abnormalities are due to non-adherence: Other factors may affect blood counts
• Inconsistent monitoring: Makes pattern recognition difficult
• Not accounting for health literacy: More than half of patients may have low health literacy 4

Strategies to Improve Adherence Assessment

• Combine multiple assessment methods (laboratory, clinical, and direct)
• Establish baseline values before initiating therapy
• Document trends over time rather than single measurements
• Create a non-judgmental environment for discussing adherence
• Consider digital tools or mobile apps for adherence tracking 4

By systematically assessing these parameters at regular intervals, clinicians can effectively determine whether patients are adhering to their hydroxyurea regimen and address barriers to improve outcomes.