Clozapine and Monitoring the Absolute Neutrophil Count

  • PixCell Medical
  • 08 May 2023

Clozapine is an atypical antipsychotic medication that has been a game-changer in the treatment of schizophrenia and schizoaffective disorders. While its efficacy in managing treatment-resistant cases is undeniable, the drug is also associated with the risk of serious side effects, including potentially life-threatening agranulocytosis.

To mitigate this risk, it’s crucial for care providers to monitor the absolute neutrophil count (ANC) in patients on clozapine therapy using an accurate complete blood count (CBC) analyzer with a 5-part differential white blood cell (WBC) count. In this article, we will delve into the workings of clozapine, the importance of ANC monitoring, and how a healthcare provider’s choice of WBC analyzer can affect patient experience and outcomes.

Understanding Clozapine

Clozapine is the most effective antipsychotic drug for treating schizophrenia. Unlike typical antipsychotics that primarily target dopamine receptors, clozapine acts on multiple neurotransmitter systems, including dopamine, serotonin, and glutamate.

However, clozapine use is limited due to its side effect profile. Most notably, clozapine can cause agranulocytosis, which is a severe drop in neutrophils that can leave patients vulnerable to infections. This side effect is rare, occurring in approximately .04% of patients, but it is essential to monitor patients closely to prevent potentially fatal complications.

Eosinophilia, which is a high count of eosinophils, is also an uncommon side effect of patients on clozapine. Other side effects include weight gain and sedation.

Monitoring the Absolute Neutrophil Count (ANC)

Absolute neutrophil count (ANC) is a measure of the number of neutrophils in the blood, which are the most common type of white blood cell and play a vital role in defending the body against infections. Monitoring the ANC is a critical component of clozapine therapy to ensure safe use of the drug and detect early signs of agranulocytosis.

In general, patients initiating clozapine therapy should have a baseline ANC value and be monitored weekly for the first six months, every two weeks for the following six months, and every four weeks thereafter. If the ANC remains within the normal range, it is considered safe for patients to continue taking clozapine.

Monitoring the ANC requires a precise complete blood count analysis with a 5-part differential, which is typically done by sending a venous blood sample to a laboratory. However, the delays associated with additional patient scheduling and waiting on lab results can affect the provider’s ability to identify problems quickly. Frequent venous blood draws can also impact the patient experience or discourage them from continuing clozapine.

HemoScreen™ from PixCell Medical is a point-of-care WBC analyzer that performs lab-grade analysis with a 5-part differential in just five minutes, allowing care providers to quickly and conveniently check ANC levels while enhancing the patient experience. It requires only a finger prick of blood and provides comparable results to the standard laboratory method.

Managing Neutropenia in Patients on Clozapine Therapy

Neutropenia refers to a low neutrophil count, which can increase a patient’s risk for infections. It is essential to identify and manage neutropenia in psychiatric patients receiving clozapine.

Here are some general guidelines for managing neutropenia:

  1. Mild Neutropenia (ANC between 1,500 and 2,000 cells/μL): Generally, no intervention is needed, but it is important to continue regular ANC monitoring and closely monitor the patient for any signs of infection.
  2. Moderate Neutropenia (ANC between 1,000 and 1,500 cells/μL): This level of neutropenia warrants closer monitoring. Increase the frequency of ANC monitoring and evaluate the patient’s condition for potential causes of neutropenia, such as concurrent medications, infections, or underlying conditions.
  3. Severe Neutropenia (ANC below 1,000 cells/μL) or Agranulocytosis: In this case, clozapine should be discontinued immediately. Patients should receive medical evaluation and treatment for any infections. Consult with a hematologist to determine the cause and management of the neutropenia. Once the ANC has recovered to a safe level, the decision to re-initiate clozapine should be carefully considered and only undertaken with close monitoring and consultation with a specialist.


Choosing the Right WBC Analyzer

Using an accurate and reliable complete blood count analyzer is crucial in monitoring clozapine absolute neutrophil count levels for patients on clozapine therapy. Although eosinophilia is a rare side effect, your WBC analyzer should also be able to provide precise eosinophil counts.

By ensuring the precision of these measurements, healthcare providers can make informed decisions about treatment adjustments, identify potential cases of neutropenia, agranulocytosis, or eosinophilia, and ultimately provide safer and more effective care for their patients.

When selecting a WBC analyzer for ANC monitoring in clozapine therapy, healthcare providers should consider factors such as:

Accuracy and Precision

Inaccurate ANC measurements may lead to unnecessary treatment adjustments or, worse, missed cases of neutropenia or agranulocytosis, putting patients at risk for life-threatening infections.

A reliable WBC analyzer should have a high degree of sensitivity and specificity, meaning it should accurately detect and differentiate between the different types of white blood cells, including neutrophils and eosinophils. In addition, it should provide consistent results, even in cases where the blood sample contains a low number of white blood cells.

When analyzed in a study, HemoScreen provided comparable results with standard venous blood laboratory methods for WBC, neutrophil, and eosinophil counts.

HemoScreen harnesses PixCell Medical’s AI-assisted Viscoelastic Focusing (VEF) technology to perform lab-grade analysis on a single blood drop sample. The device analyzes hundreds of characteristics, making it applicable to countless functions beyond ANC analysis.

Patient Comfort

Patients starting on clozapine must have weekly venous blood sampling, which has been cited as a reason for either refusing to start clozapine or discontinuing it. Rather than frequent blood draws from a vein, a CBC analyzer that can use capillary blood samples drawn from a finger prick is a significant advantage for psychiatric patients.

When studied, finger prick point-of-care analysis was found suitable for monitoring blood counts in patients on clozapine. Patients may still require confirmatory standard venous testing if results are far below acceptable thresholds, but initial testing from a finger prick makes the monitoring process more comfortable and acceptable to psychiatric patients.

HemoScreen can measure CBC with a 5-part differential using a capillary blood sample from a finger prick or a venous sample drawn from a vein. This gives patients a choice in how they’d prefer to provide a blood sample and can overall enhance patient comfort throughout monitoring.

Ease of Use and Speed

The device should be user-friendly and require minimal training for healthcare providers to operate. This makes point-of-care solutions more accessible to healthcare facilities and ensures physicians can receive crucial data without being bottlenecked by staffing shortages.

Furthermore, rapid turnaround times for results are essential in monitoring clozapine absolute neutrophil count levels, allowing for timely decision-making in patient care.

HemoScreen provides results within just five minutes, eliminating the need for outside lab work. The procedure is fully automatic, requiring minimal training, no maintenance, and no calibration.


The analyzer should be cost-effective in terms of initial investment, ongoing maintenance and costs, and impact on patient experience.

Finger prick testing is greatly preferred by patients on clozapine. Patients who discontinue or refuse clozapine due to frequent venous testing may be more willing to start and remain on clozapine if they only need to provide capillary finger prick blood samples. Starting patients on clozapine has been associated with significant reductions in healthcare provider costs, which can justify the initial outlay for the HemoScreen device.

Additionally, many WBC analyzers on the market require reagents to function, which adds to the overall cost of ownership. HemoScreen is the only device on the market that uses cartridges instead, which can save health facilities on labor associated with maintenance and calibration as well as recurring inventory management costs for reagents.

Simplify Real-Time Blood Testing

For health practitioners monitoring the absolute neutrophil count of patients on clozapine, accuracy is only one factor when it comes to blood testing. A fast, accessible point-of-care WBC analyzer that requires only a finger prick of blood can provide rapid results for critical decisions when it matters most.

HemoScreen is the first compact, easy-to-use hematology analyzer that provides a full 5-part differential complete blood count within five minutes. Care providers can monitor and diagnose patients for neutropenia in a single visit with HemoScreen’s lab-accurate results, leading to faster patient care without compromising on quality.

To learn more about how HemoScreen can help your healthcare facility monitor absolute neutrophil counts for psychiatric patients on clozapine, contact PixCell Medical to schedule a demo.


(*) Please note: training must be defined by local, state and federal regulations. In the USA, training is defined for CLIA moderate complexity devices.