Essential Records for Intermediate Checks in a Microbiology Laboratory

In every microbiology laboratory, accurate and reliable test results depend on the proper functioning of equipment. Equipments like autoclaves, incubators, pH meters, and balances are used daily for testing and positive culture work. Over time, however, these instruments may show small variations due to regular use, environmental changes, or mechanical wear and tear. To ensure consistent performance between two calibration intervals, intermediate checks are required.

Intermediate checks are routine verifications carried out on equipment to confirm that it continues to perform as expected after calibration and before the next scheduled calibration. Intermediate checks act like regular check-ups for laboratory instruments. It help in early detection of any drift or malfunction, ensuring that test results remain accurate and dependable. According to ISO/IEC 17025:2017, particularly clause 6.4.10, laboratories must perform intermediate checks to maintain confidence in the calibration status of their equipment.

These checks are extremely important in microbiology laboratories because even minor deviations in temperature, pressure, or pH can directly affect microbial growth and test results. For example, if an incubator is not maintaining the correct temperature or an autoclave fails to reach proper sterilization conditions, it can lead to inaccurate results or contamination. Therefore, performing intermediate checks is not just a quality requirement but also an important part of laboratory safety and reliability.

Common equipment used in microbiology labs and their recommended intermediate checks include the following: Autoclaves should be verified using Bowie-Dick tests, chemical and biological indicators to ensure proper sterilization. These checks are typically done daily or weekly, and the results are recorded in the autoclave logbook. Incubators and hot air ovens should be checked daily with a calibrated thermometer or data logger to ensure that the internal temperature is within the acceptable range, usually within ±2°C of the set value. Refrigerators and deep freezers should also be monitored daily to maintain the required temperature for sample and media storage.

For analytical instruments like pH meters, it is essential to verify readings daily using standard buffer solutions (pH 4.0, 7.0, and 9.2). The reading should not deviate more than ±0.1 pH units from the true value. Balances used for weighing reagents or samples should be checked daily with standard calibrated weights to ensure they provide accurate measurements. Similarly, micropipettes should be verified monthly using the gravimetric method to confirm volume accuracy within ±1%.

In microbiology labs where Laminar Air Flow (LAF) cabinets or biosafety cabinets are used, intermediate checks include verifying HEPA filter integrity. Airflow should remain between 0.36 to 0.54 m/s to ensure effective air sterilization and exposure of plates is required to ensure a contamination-free environment for analysis. Microscopes should be checked regularly for proper focus, illumination, and mechanical movement. Other instruments such as water baths, orbital shakers, and colony counters also require periodic verification to confirm they are working correctly.

All intermediate check results must be properly documented in a dedicated Intermediate Check Register or Equipment Verification Logbook. Each record should include the date of verification, equipment name and ID, parameter checked, result obtained, acceptance criteria, and the name of the person performing the check. These records serve as important evidence during NABL or ISO 17025 audits, demonstrating that the laboratory maintains control over its equipment between calibrations.

Performing intermediate checks has several benefits. It helps in maintaining the accuracy of test results, prevents the use of faulty equipment, minimizes non-conformities during audits, and ensures compliance with national and international quality standards. It also builds confidence among laboratory staff and clients that test results are scientifically valid and reliable.

To make intermediate checks more effective, laboratories should always use calibrated reference instruments for verification. Checks should be performed before starting routine work, and any deviation from acceptable limits should be reported immediately to the quality manager for corrective action. Regular review and trending of intermediate check data can also help identify gradual changes in equipment performance, allowing preventive maintenance before failure occu

Intermediate checks ensure that laboratory instruments are stable, and trustworthy every single day — not just on the day of calibration. It is a step that makes a big difference in the reliability of microbiological testing. Every accredited or quality-conscious laboratory should make intermediate checks a daily habit because maintaining quality is not a one-time event, it’s a continuous process.