How Accurate?

The lab made a mistake!

Everyone working in the laboratory cringes when these words are heard. No one likes or wants to make a mistake, especially when the consequences are potentially life-threatening. Unfortunately, mistakes do occasionally occur. However, the mistake may occur at many levels and may not necessarily be the fault of the laboratory.

We are often asked, How accurate are the laboratory tests? Translated...Can I trust these results?

Think about the events that occur from the time your blood or urine sample is taken until the time the laboratory report is generated.

1. Proper Laboratory Test Selected

The physician ordering the test must be careful to order precisely what is wanted. A Lupus test may be misinterpreted as a request for a Lupus panel or a Lupus Inhibitor panel. If the precise terminology is not used, the risk for an incorrectly ordered test is increased.

2. Proper identification

As simple and as basic as this sounds, patient identification labels can be wrong. The laboratory phlebotomist is trained to confirm the name of the patient but sometimes the patient is unable to answer. In other circumstances, two patients with the same name may be confused. There is always a cross check with a unique hospital identification number but it is easy to see how a potential mistake can be made if one is not vigilant.

3. Proper Technique To Obtain the Specimen

The laboratory phlebotomist does not always draw the specimen. Nurses, medical students, physician's assistants, any number of medical professionals may draw a blood sample. There is a proper technique to obtain a blood or urine sample. Some patients have an intravenous (IV) line in one of the arm veins. If a blood sample is taken from one of these lines, care must be taken to not contaminate the blood sample with the IV solution. Some IV solutions contain glucose which can lead to a spurious increase in the blood glucose measurement if the sample is contaminated with it.

Error or Variation?

If the body's temperature can vary from minute to minute, it should come as no surprise that the chemicals and enzymes that are measured can also vary with similar rapidity. But did you know that even a change in posture may change some laboratory values? Some values, such as blood glucose, will directly be influenced by a recent intake of a meal. Other values, such as magnesium, are less likely to be affected. All of these conditions which may alter the laboratory value before the actual blood sample or specimen is taken are known as pre-analytical variables. Careful attention to potential pre-analytical variables can often resolve puzzling laboratory values.

Errors can occur, however. The prudent course of action is always to repeat the laboratory test to ensure that the value which was first reported is accurate. If the two values differ significantly, sometimes an additional sample can be requested. In addition, a careful check of the quality control samples (see next section) is made to ensure the equipment is functioning properly.

Quality Control and Quality Assurance

These two terms describe similar concepts and are related. Quality control (QC) involves the monitoring of intraday and intratest variation. Quality Assurance (QA) is the ongoing assurance that the laboratory tests are measuring what is intended to measure. Every laboratory test is performed with several control samples, a sample which has a known premeasured value. In addition, any value which is out of the usual range can be analyzed again to ensure that it is a true value. Any aberrant value which is confirmed is immediately reported to the physician ordering the test.

Accreditations

The laboratory is one of the most highly regulated areas in medicine. There are several levels of accreditation. Every laboratory must have a CLIA license (Clinical Laboratory Investigation Act). In addition, a hospital based laboratory must be accreditated by the JCOAH (Joint Commission of Accreditation of Hospitals). This is the same agency which inspects hospitals and certifies them for operations. The highest level of accreditation for all laboratories in the United States is CAP (College of American Pathologists) accreditation. The CAP maintains a rigorous set of standards which usually exceeds the other certifying agencies' requirements. In fact, JCOAH will often waive the inspection of the laboratory if it is CAP accreditated.

The blood bank is subject to even more rigorous regulations. In addition to the above mentioned agencies, the blood bank must answer to two additional federal agencies, the FDA (Food and Drug Administration) and the Department of Health. Blood and blood products are regarded as drugs and thus must be regulated as such. These products are also perishable with a finite shelf life and subject to different regulations than reagents used in chemistry or hematology. Finally, there is an even higher level of accreditation, unique to blood banks. This is the AABB (American Association of Blood Banks). All blood banks aspire to this level. Their standards are the most rigorous in the entire laboratory field.

Proficiency Testing

I took my last test in school!

You did...but we have tests several times a year. After accreditation is achieved, a laboratory must demonstrate continued excellence in all areas where testing is offered. Testing varies for the different areas of the laboratory. For hematology, it may involve review of kodachrome slides demonstrating different blood cells. In chemistry, serum samples are provided and the appropriate tests are evaluated. In microbiology, unknown microbial cultures are provided and identification of the microbe is required..

The answers are submitted to the agency, graded, and then returned. Any wrong answer requires a written explanation. Failure of the testing may lead to a site visit by the inspecting agency. Your laboratory results are also compared to all of the laboratories participating in the testing to assure the testing is fair and also to provide a measure of accuracy. When the laboratory is reinspected (usually every 2 years), all of the proficiency testing is reviewed and the past performance is a critical factor in recommending re-accreditation.

Summary

It may come as a surprise to many of you how highly regulated the laboratory is. The modern laboratory requires state of the art equipment directed by state of art people. You cannot trust your laboratory results with anything less.