Calibrating Digital Timers

A blood banker wrote that her lab uses calibrated digital timers to time their antibody screen and other tests performed in the Transfusion Service. The digital timer has a certificate of calibration and a due date for calibration that is two years from the previous one. The inquring blood banker wants to know if it is an acceptable practice to use a timer with a valid calibration certificate to re-calibrate other timers that are due for their re-calibration?

Before sharing the above question with the full e-Network Forum, expert opinion was solicited. According to a Technical Specialist of the Laboratory Accreditation Programs of the College of American Pathologist (CAP), regarding electronic timer checks, the above suggested method for verifying calibration of timers is acceptable. There are no specific checklist items in the Transfusion Medicine Checklist (MS Word) (PDF) that address calibration of digital timers used for timing blood banking tests.

Please share with the e-network forum your local policy/procedure for recalibration of digital timers that are used in your laboratories.

The following responses have been received:

ADDENDA April 16, 2002

1. One blood banker reported that his blood bank calibrates its timers with the National Oceanographic and Atmospheric Administration (NOAA) via telephone. NOAA is considered to be the authority on atmospheric and oceanographic conditions including time. The telephone number for the automated system is (303) 499-7111. At the start of the tone, the stopwatch started. At the end of the tone (1 minute), the stopwatch is stopped. The difference variance is then recorded. Variance limits are +/- 1 second. They report not having had any problems with their regulatory and accrediting agencies by performing QC this way.

ADDENDA April 22, 2002

2. A blood banker in Arizona reported that according to their Biomedical Department, digital timers on equipment such as MTS centrifuges and Sorvall Cell washers are considered 'synchronous timers'. The calibrated time does not vary for these timers. Thus, at the Arizona blood banker's facilities, calibrations are performed only on receipt and after repairs to the instrument. Stopwatches, battery-operated timers, and other mechanical timers are calibrated on receipt and quarterly. The responding blood banker says that the inspectors who have been to their 8 locations have not argued this logic.

Please submit comments to the e-Network Forum.

Ira A. Shulman, MD
CBBS e-Network Forum Editor & Moderator