Key elements in a successful pediatric laboratory

Another important facet of the pediatric laboratory is the facility to test for metabolic and genetic diseases.

In addition, children’s conditions are often more labile than those of adults, which creates the need for rapid testing, often at the bedside (point-of-care testing).

Adolescents, even when seemingly healthy, are subject to many social diseases or conditions. The use of drugs of abuse is most common in this age group. Teenage pregnancy, sexually transmitted diseases, and suicide are all factors that have an impact on the pediatric laboratory.

This paper will focus primarily on the needs of neonates and infants in Pediatric Intensive Care Units (PICU).

The newborn is highly vulnerable to the physiological changes needed for extrauterine life. This is particularly true for the premature infant who enters life too early in the gestational period. The highest risk neonates are those born at less than 1 kg at birth. In the Neonatal Intensive Care Unit (NICU) at our hospital, we see about 90-100 such infants yearly. Our NICU has 40 beds, which are almost always in use. 

The major conditions seen are prematurity, hyaline membrane disease, sepsis, pneumonia, meconium aspiration, and congenital heart disease. Though less common, metabolic and other genetic diseases create a challenge to the neonatologist.

In recent years, the introduction of Extracorporeal Membrane Oxygenation (ECMO) has saved the lives of many prematures presenting with meconium aspiration, as well as for those neonates with postsurgical cardiac failure. ECMO essentially effects cardiac support for those children who have reversible respiratory failure.

In our PICU, which has 16 beds, the most common conditions seen are also related to pulmonary or cardiac diseases. Those most frequently seen include: respiratory dysfunction, postoperative cardiopulmonary or other postoperative conditions, pneumonia, bronchiolitis, metabolic disturbances, and sepsis.

Blood collection 

FIG. 1: Sites of Collection from an Infant’s Heel.
From: Blumenfeld TA, Tri GK, Blanc WA. Recommended site and depth of newborn heel skin punctures based on anatomical measurements and histopathology. Reprinted with permission from Elsevier Science (The Lancet 1979; 1: 231).

In 1986, the National Committee for Clinical Laboratory Standards (NCCLS) published “Procedures for the Collection of Diagnostic Blood Specimens by Skin Puncture” [1]. The sites of collection from an infant’s heel were recommended by Blumenfeld [2], and are reproduced from the book by Soldin, Rifai and Hicks [3]. The exact details, as outlined in these references, are illustrated graphically in Fig. 1. 

Venipuncture is the method of choice for the collection of blood from older children, who are less likely to be traumatized by the sight of a needle than younger children! Specimen volume is of great concern for premature infants and children. 

As mentioned above, we take care of many babies under 1 kg in weight, whose total blood volume is less than 115 mL. Hicks [4] recently published a letter in the New England Journal of Medicine describing her survey of the amounts of blood drawn for various tests in major teaching and community hospitals. 

Her conclusion was that many laboratories draw far more blood than is necessary, and this practice is unacceptable for pediatric patients. Fig. 2 shows the average blood volume by age for prematures, newborns, and infants. Table I shows the hematocrit by age. 

It is obvious that, as hematocrits are high and blood volumes low, it is essential to keep blood drawing to a minimum, otherwise replacement transfusions may be necessary.

FIG. 2: Infant Blood Volume.
From Werner M, ed. Microtechniques for the clinical laboratory. New York: Wiley, 1976:2. Reprinted with permission.

The other major consideration with small specimens is the effect of leaving such samples uncovered, which can lead to evaporation of the liquid in the sample [5]. For example, it is generally observed that evaporation can easily lead to a 10 % fluid decrease from a 100 µL specimen.

The choice of instrumentation is critical, although much easier now than 20 years ago. It is preferable to have all analyses performed on 20 µL or less of serum or plasma. It is also important to understand the significance of the “dead volume” required in the sample cup of automated analyzers, that is, the amount of sample that remains in the cup after samples are aspirated for analyses.

Obviously, these considerations are less serious in laboratories devoted to adult patients.

Metabolic and genetic diseases 

It is important to note that it is in the neonatal period that many of these diseases become manifest, and if not treated expeditiously, can result in mental retardation or death. Some such diseases include: galactosemia, maple syrup urine disease and ornithine transcarbamoylase, to mention only a few. 

A metabolic disease should always be considered in a neonate with “failure to thrive” and unexplained metabolic acidosis. Hepatosplenomegaly, muscle weakness and bone abnormalities may also lead one to suspect a metabolic disease. The first line of testing includes analyses of amino acids and organic acids.

With the recent elucidation of the human genome, it is clear that many more gene-linked diseases will be identified, and that the methods of choice for diagnosis of such diseases will consist of molecular diagnostic techniques, such as the use of DNA chips and single nucleotide polymorphisims (SNP).

Reference ranges 

Again, this is a topic for an entire paper, but suffice it to say here that many test values change dramatically with age. For example, the reticulocyte count is 2.2-4.8 % from 1-3 days after birth to 0.4-2.7 % at 4-30 days after birth. Thyroxine is 3.0-14.4 µg/dL at 1-30 days to 5.3-16.3 µg/dL at 1-20 months. 

The reader is directed to reference [6] that is dedicated to this topic. It is obviously necessary to have age-related reference value ranges, otherwise unnecessary additional testing could be ordered.