Why do I say pediatric labs are different? A blood test is a blood test, right? Of course it is, however there are a lot of aspects of operating a pediatric lab that really are different from the way operations run in a lab whose clientele is mainly adults.
Most people can think of the most obvious difference: age-related reference intervals. The concentration of various biomarkers in the body changes as an infant grows and develops into an adult. In some cases, there’s not a lot of change in the biomarker. A blood pH is pretty constant over the course of a person’s life, as are the electrolytes. The reference intervals for these may be broader in infancy, but in general they don’t change a lot. However some biomarkers change so drastically that normal levels in childhood would be considered pathological in an adult. Without reference intervals tied to age or developmental state, these tests are not able to be properly interpreted. Alkaline phosphatase during bone growth and steroid hormones during puberty are two good examples of this.
The things that people tend not to think about that cause a pediatric lab to be different are predominately all centered on issues with sample volume. Especially in infancy, children have limited blood volume for testing, and this fact affects nearly every operation in a pediatric laboratory.
Front end processing of samples is affected, as often more than 60% of the tubes arriving in the lab are microtubes, which hold 1 mL or less. These tubes may not be able to hold a barcode label, nor fit on an instrument robotic system. The sample must be aliquotted into tubes that will fit a system, or hand fed into an instrument, and often hand-programmed into the instrument. More manual steps results in more opportunities for human error. In addition, the amount of sample used by any given instrument for testing must be considered. That sample volume includes the actual volume necessary for analysis, plus the volume necessary to run HIL (hemolysis, icterus, and lipemia) indices and the instrument dead volume (the volume below which an instrument cannot pipet the sample). Instruments with large dead volumes will not be found in pediatric labs.
Small sample volumes also affect the ability of the lab to add-on tests to samples already in the lab, or rerun samples later to check results. There may be insufficient volume to run more tests or rerun tests, or the sample may have evaporated and be unacceptable for running additional analyses. A study done using a 5 mL serum sample and a 0.1 mL serum sample and allowing both to sit open to the air for 4 hours showed that the 5 mL serum sample had less than 10% difference between original test values and those run 4 hours later. The 0.1 mL sample had more than 50% difference in its values. In addition, with just enough sample to run a test one time, if a dilution needs to be made, it may not be possible.
Lastly, there are a few test menu differences in a pediatric laboratory. Tests commonly found in pediatric labs, but essentially never in predominately adult labs include things like testing for inborn errors of metabolism and sweat chloride testing for Cystic Fibrosis. Conversely, common tests in an adult lab that are not performed in a pediatric lab include serum protein electrophoresis, PSA and other tumor markers. Some tests are performed in both labs but for different indications. For example, AFP is used as a tumor marker for hepatocellular carcinoma in pediatrics instead of as a maternal prenatal screening tool like in an adult lab.
These are some of the ways in which pediatric lab medicine differs from adult lab medicine, and offers unique challenges in day to day operations.
-Patti Jones PhD, DABCC, FACB, is the Clinical Director of the Chemistry and Metabolic Disease Laboratories at Children’s Medical Center in Dallas, TX and a Professor of Pathology at University of Texas Southwestern Medical Center in Dallas.