A carryover study in haematology equipment or other autoanalyzer assesses the potential for sample carryover, which occurs when traces of a previous sample remain in the system and affect the accuracy of subsequent measurements. Performing a carryover study is essential to ensure the reliability of test results and patient safety. Here’s how to conduct a carryover study in haematology equipment, along with an example:
Carryover Study Steps:
- Select Test Samples:
Choose a set of samples with different levels of the analyte of interest. Include low, normal, and high concentrations to cover the entire range.
- Prepare the System:
Ensure the haematology analyser is in proper working condition, calibrated, and ready for testing.
- Initial Blank Run:
Run a blank (negative control) sample through the analyser. This helps clear any residual sample material from previous runs.
- High-Concentration Sample:
Run a high-concentration sample (Sample A) through the analyzer. Record the result.
- Blank or Low-Concentration Sample:
Run a blank (negative control) sample or a low-concentration sample (Sample B) immediately after Sample A. This assesses whether any carryover from Sample A affects subsequent measurements.
- Calculate Carryover:
Calculate carryover using the formula: Carryover (%) = (Result of Sample B – Result of Blank) / Result of Sample A x 100
- Repeat Steps:
Repeat steps 4 to 6 with different samples (high and low concentrations) to assess carryover across the analyte’s measurement range.
- Analyze Results:
Evaluate the calculated carryover percentages. If carryover exceeds acceptable limits, corrective actions are needed.
- Reporting:
Document the study procedure, results, and any corrective actions taken. This documentation is essential for quality control and regulatory compliance.
Example:
Let’s say you’re conducting a carryover study for a haematology analyser measuring hemoglobin (Hb) levels. Your analyzer measures Hb in g/dL.
Sample A (High Concentration):
Result for Sample A = 15.2 g/dL
Sample B (Blank or Low Concentration):
Result for Sample B = 12.8 g/dL (after running Sample A)
Result for Blank = 13.0 g/dL (initial blank run)
Using the formula: Carryover (%) = (Result of Sample B – Result of Blank) /
Result of Sample A x 100
Carryover (%) = (12.8 – 13.0) / 15.2 x 100 = -1.31%
In this example, the calculated carryover is -1.31%, which indicates that there is no significant carryover from Sample A affecting the measurement of Sample B. Negative carryover suggests that the system is effectively clearing any residues from previous samples.
Remember that acceptable carryover limits vary based on laboratory standards, manufacturer specifications, and the clinical significance of the analyte. If calculated carryover exceeds acceptable limits, further investigation and corrective actions are necessary to address the issue.
About the author
Dr. Sambhu Chakraborty is a distinguished consultant in quality accreditation for laboratories and hospitals. With a leadership portfolio that includes directorial roles in two laboratory organizations and a consulting firm, as well as chairmanship in a prominent laboratory organization, Dr. Chakraborty is a respected voice in the field. For further engagement or inquiries, Dr. Chakraborty can be contacted through email at director@iaqmconsultants.com and info@sambhuchakraborty.com. Additional resourcesand contact information are available on his websites, https://www.quality-pathshala.com and https://www.sambhuchakraborty.com, or via WhatsApp at +919830051583