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Specimen Minimum Volume

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Published: January 2011

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Dr. Dale discusses the patient focus in the development of specimen minimum volumes (SMV), where to find the SMV in Mayo’s test information, and how to optimize your testing by using the correct volume for your patient’s situation.

Presenter: Jane C. Dale, MD of the Division of Laboratory Medicine and Pathology at Mayo Clinic

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Welcome to Mayo Medical Laboratories' Hot Topics. These presentations provide short discussions of current topics and may be helpful to you in your practice.

Our presenter for this program is Dr. Jane Dale, a consultant in the Department of Laboratory Medicine and Pathology at Mayo Clinic. Dr. Dale discusses the patient focus in the development of specimen minimum volumes (SMV), where to find the SMV in Mayo's test information, and how to optimize your testing by using the correct volume for your patient's situation.

Iatrogenic Anemia

The amount of blood needed to perform a laboratory test is a concern of laboratorians, as well as a concern of patients and their family members. Why do we care?

The terms iatrogenic anemia, nosocomial anemia and investigational anemia are applied to the anemia that results from blood loss due to repeated venipunctures for the purposes of obtaining specimens for laboratory testing. This type of anemia is not uncommon and is most often seen in seriously ill hospitalized patients who are tested frequently and in infants with small blood volumes.

Adverse Consequences of Anemia

The anemia can result in serious adverse effects, most notably shortness of breath and fatigue due to decreased delivery of oxygen to tissues. When significant anemia occurs, transfusions may be required, and transfusions carry their own set of risks.

Specimen Volumes Have Decreased Over Time

As laboratory instrumentation technology has advanced, the amount of sample needed for testing has decreased. For example, when I began my career in the laboratory, we drew 15 mLs of blood for a routine chemistry profile that consisted of 12 analytes. Now, we routinely collect 5 mLs to perform those12 tests, and when necessary, we can perform them using much less. So, we have made a lot of progress, thanks primarily due to miniaturization of the handling and analytic components of testing equipment. Technological advances make it possible to perform testing on smaller and smaller amounts of sample, amounts that can be accommodated by micro-collection containers. However, those advances are often off-set by the increased use of laboratory automation systems that allow hands-free specimen processing and testing because most automation systems work best with standard, nonmicrosized collection containers. Nevertheless, we continue to watch how much blood we require because it is in the best interest of the patient and because healthcare providers, patients and their families expect us to do so.

Specimen Volume Reduction Initiatives at Mayo

In the past 10 years, the laboratory staff at Mayo have conducted a number of quality improvement initiatives aimed at reducing blood specimen volume requirements. In this presentation I would like to present a few of them, show where we provide specimen volume requirement information, and discuss the implications of submitting too little specimen to our laboratory.

Specimen Minimum Volume (SMV) Definitions

One of our first projects was to establish, across all laboratories and all tests at Mayo, a standard definition of the minimum volume required to perform a test. We called this amount "specimen minimum volume" and developed 2 different definitions, 1 for automated tests and another for manual assays.

Automated Assay SMV

For automated assays: The "specimen minimum volume" is the amount required to perform the assay once, without giving a low-volume instrument alarm. This includes instrument pick-up volume (or analytic volume), instrument dead space, and container dead space. It does not include enough to perform repeat or additional testing.

Manual Assay SMV

For manual assays: The "specimen minimum volume" is the amount required to perform the assay once with operator assistance and includes pipetted volume instrument dead space, and container dead space.

Locating Minimum Volume on the Test Catalog

The "minimum volume" is listed under a header with that name in our electronic test catalog. It is also included in our paper catalog.

Specimen Minimum Volume

By applying a standard definition, and requiring use of it, we decreased volume requirements for the majority of our tests. For example, using a sample of the 35 most frequently ordered tests, we decreased the requested volume for approximately 70% of the tests.

Comparison to 5 Commercial Labs

Because we receive specimens from patients outside our medical system, we also wanted to see how our volumes compared to commercial reference laboratories. For our top 50 tests, and the top 25 tests requested by our children's hospital clients, we found that our volumes were the lowest for 50% of tests, or second lowest for an additional 25% of tests, compared to 5 commercial laboratories.

Specimen Volume Review

We are committed to reducing specimen volume requirements for the tests we perform, and continue to emphasize that aspect of patient care when we select new instruments and develop new tests. Specimen volumes are established whenever we introduce a new test. And they are evaluated during the annual review of our existing testings. Tests with high specimen volume requirements are targeted for method modifications and replacement with new tests, or new analytic methods, that do not present that problem.

25-OH Vitamin D: Minimum Volume Requirements

An example of this is our vitamin D test. 25-Hydroxyvitamin D is the preferred test for the evaluation of possible vitamin D deficiency or excess. For many years, we used high performance liquid chromatography (abbreviated HPLC) to do the test, and that method had a very high volume requirement—originally, 3 mL of serum was the minimum amount needed to perform the test. That volume requirement pushed our scientists to develop an assay that did not require so much sample. Subsequently, we replaced the HPLC vitamin D assay with a mass spectrometry assay that is analytically superior AND can be done on as little as 0.25 mL.

Specimen Required or Minimum Volume

When you access the information in Mayo Medical Laboratories' paper or electronic test catalogs, you'll see there is a "Specimen Required" field and a "Minimum Volume" field. The amount requested in the "Specimen Required" field is our preferred volume, which has been established to optimize testing. On the example shown in this slide, our preferred volume is 2.2 mL. That amount allows the laboratory to quickly process specimen containers, present the containers to the instruments, and perform repeat testing, if necessary. Because many of our testing processes are fully automated, this volume allows hands-free processing and testing, and our quickest turnaround time. Because patient values are frequently abnormal, repeat testing, dilutions, or other specimen manipulations often are required to obtain a reliable, reportable result. Our preferred specimen requirements allow this to occur in a timely fashion.

However, when the venipuncture is technically difficult or the patient is at risk of complications from blood loss (such as pediatric or intensive-care patients), it frequently becomes a question of the smallest amount of specimen Mayo can successfully analyze. This is where specimen minimum volume becomes significant. In this example, the minimum volume is 1.1 mL.

Specimen Required Field

It is important to understand the definitions of Mayo's preferred and our minimum specimen volumes, as well as the consequences of deviating from the recommendations. Submission of preferred specimen volume optimizes testing, by providing the fastest turnaround time while also allowing for repeat testing, dilutions, and/or follow-up testing, if necessary, thus assuring that a reportable result will be obtained in a timely fashion.

Minimum Volume Field

Appropriate use of minimum volume information helps caregivers minimize the amount of blood drawn from the pediatric or difficult patient. But, submitting less than the preferred volume may negatively impact the quality of care by slowing turnaround time, increasing the hands-on personnel time (and cost) required to perform the test, and making it impossible to perform necessary follow-up testing in many cases. Specimens that are less than the minimum volume will, in most cases, be insufficient for analysis (and will be flagged as QNS, or quantity not sufficient).

Submitted Volume

So, when patient conditions do not mandate reduced collection volumes, we ask that our clients submit the preferred volume to facilitate rapid, cost-effective, reliable test results, reserving minimum volume submission to those exceptional cases.

Finally, please recognize that Mayo staff will make every possible effort to successfully test your patient’s specimen. In some cases, because of volume limitations, specimens will be inadequate for the desired testing. But, if you have concerns about submitting a specimen for testing, please call Mayo Laboratory Inquiry at 800-533-1710. Our staff can discuss the testing you desire and the specimen you have available, and determine if testing can be performed, possibly using alternative techniques.

Together we can assure that our patients receive the testing that they need, while at the same time minimizing the risk of phlebotomy-induced anemia.