Paul G. Catrou

Analytical interference. More than just a laboratory problem.

Specimen integrity is an important preanalytic factor that affects the accuracy and clinical utility of laboratory test results. Some common preanalytic factors that result in the rejection of specimens from analysis include the use of improper collection containers, excessive time delay from specimen collection to analysis, failure to store specimens at an appropriate temperature prior to analysis, failure to shield the specimen from direct light, and collection of the specimen at the wrong time of day or at an inappropriate time after administration of certain pharmacologic agents.1 While most laboratorians can readily identify these factors as responsible for some types of measurement error or leading to incorrect interpretation of test results, it should be recognized that they account for well less that half of the reasons for rejection of specimens by the clinical laboratory. The most common preanalytic factor affecting the acceptability of specimens for analysis is the presence of interfering substances within the specimen. The presence of interfering substances alters the correct value of the measured result and may lead to inappropriate clinical intervention and compromise patient outcome. The article by Tang et al2 in this issue of the Journal attempts to address one important aspect of point-of-care glucose monitoring devices, ie, interference effects from pharmacologic agents administered to patients in the critical care setting. Although the investigation of interference effects should be the responsibility of the instrument manufacturer, Tang et al note that information provided by the manufacturer concerning interference effects is often too vague to be of value. Manufacturers’ performance claims regarding interference effects often do not specify what the manufacturer considers “significant” interference, the concentration or activity of the analyte of interest within the specimen investigated for suspected interference, or the actual experimental protocol used for investigating interference effects. From the manufacturer’s perspective, this approach of providing simple statements with respect to interference claims is justified on the grounds that providing laboratorians more detailed information about assay interference is not helpful, because the actual concentration of the interfering substance is rarely known.3 While this may be true for certain drugs that are not routinely measured in patients, many medications that do interfere with analytical methods, eg, the interference from acetaminophen identified in the current study, are routinely measured in most clinical laboratories. In addition, interference effects due to hemolysis, bilirubinemia, and lipemia can be easily ascertained, since many of the automated clinical chemistry systems now are able to provide quantitative measurement of these common interfering substances. However, some instrument manufacturers that do offer hardware capable of performing quantitative measurements of these common interfering substances still provide nebulous interference claims. For example, although the Hitachi 747 system (Boehringer Mannheim, Indianapolis, IN) can accurately measure serum hemoglobin concentrations, the interference claim for hemolysis from the manufacturer’s alanine aminotransferase assay states that “RBC contamination may elevate results....”4 This information is clearly insufficient to allow the user to make an informed decision about the effect of a potential interferent, regardless of the instrument’s ability to provide quantitative measurement of serum hemoglobin concentrations. Another approach that manufacturers can take to provide interference claim information is to supply the user with quantitative statements such as, “Compound x, at a concentration of 100 mg, may decrease results by 10%.”3 This type

Estimating supply requirements for implementing a laboratory information system.

The implementation of a new laboratory information system requires the total commitment of all laboratory personnel. Difficulties both within and external to the lab are to be expected as the lab and the hospital staff learn to use the system. Proper planning prior to implementation will avert additional problems that can arise due to an inadequate supply inventory. The purpose of this paper is to discuss methods of estimating supply requirements, as well as to point out other operational considerations related to system start-up.

Laboratory equipment maintenance contracts

The increasing level of technical sophistication and complexity found in clinical laboratory instrumentation today more than ever demands careful attention to maintenance service needs. The time-worn caution for careful definition of requirements for acquisition of a system should also carry over to acquisition of maintenance service. Guidelines are presented for specifications of terms and conditions for maintenance service from the perspective of the laboratorian in the automated clinical laboratory.