History of clinical chemistry in a children's hospital (1914-1964).

The historical development of a charitable children's hospital and the evolution of its clinical laboratory are presented. With the appearance of practical quantitative blood chemistry tests in the period between the two World Wars, applications to pediatrics were hampered by the need for ultramicro procedures then unavailable and for improved skin-puncture blood sampling. World War II brought economic demands that forced the hospital to privatize its beds and to charge fee-for-services. In turn, this brought added income, allowing the hiring or subsidizing of a professional staff, including the clinical chemist. The development of ultramicro blood chemistry followed, along with improved skin-puncture technology.

A study of experimental lancets for blood collection to avoid bone infection of infants.

We describe a study made at two pediatric centers to test experimental lancets for blood collection by skin puncture of infants' heels or fingers. Our primary goal is to decrease the hazard of osseous injury while collecting adequate blood, by using three lancet widths at a constant length of 1.0 mm. The three widths used were 1.0, 1.25, and 1.5 mm. When success at skin puncture was defined rigidly on the basis of the blood volume obtained, the data show that success was related neither to the lancets' dimensions as tested nor to the age of the child, but rather to the phlebotomist's skill and experience, which improved with time.

Optimal sites and depths for skin puncture of infants and children as assessed from anatomical measurements.

Postmortem measurements were made of distances from skin surface to underlying bone/cartilage on 43 children (up to 8 y old; weights from 0.7 to 26.4 kg) to determine optimal sites and lengths of lancet tips for skin puncture of the heel, great toe, and middle finger. For measuring depths, a needle-like probe was devised that minimized disfigurement. As long as the infant's heel was available for puncture prior to callus formation (to about six months), it offered the greatest depth and the bone/cartilage of the lateral/medial sites was considerably deeper than posterior sites. At age six months, the mean distance of skin surface. At age six months, the mean distance of skin surface to bone/cartilage in the middle finger was 2.5 mm, the lower 95% prediction interval being 1.5 mm. Lengths of lancet tips for finger puncture should therefore be made less than 1.5 mm. To get the desired volumes of blood, a compromise must be reached between depth and width of the lancet tip.

Skin-puncture and blood-collecting technique for infants: update and problems.

This is updated information on acceptable practice in skin puncture and blood collection in infants, as well as on the devices used, with the additional aim of emphasizing major problem areas and some tentative solutions. Consensus standards for skin puncture have little experimental support, and evade the hard fact that studies are needed to clarify optimum sites for puncture and depth and width of lancets, and to assess the effects of compression and skin resistance in the puncturing process. Preliminary data revealed that the puncturing depth of 2.4 mm recommended for the newborn is excessive. In four of 14 newborns at necropsy, the distance from posterior planar skin surface to underlying bone ranged between 2.0 and 2.2 mm. An experimental lancet, with a 1.8-mm tip length and a diameter of 0.79 mm yielded customary blood volumes from newborns in three of the four pediatric centers where it was tested. Lack of success with the lancet was attributed to inexperienced phlebotomists, not to the lancet's decreased size. Also reviewed are problems with common devices used, and the need for examining the "economy" of blood collection.

Diagnostic quality of laboratory tests as evaluated by graphic comparison of "first test" data, with Reye's syndrome "workup" assays as a model.

In the absence of predictive values for quantitative tests ordered in particular diseases, we approximated the comparative diagnostic merit of such tests by graphically reviewing hospital experience with those diseases. As a model, we examined the usefulness of the five chemical tests most commonly ordered on admission as part of the "Reye's workup": aspartate and alanine aminotransferases, NH3, prothrombin time, and glucose. We expressed the data as multiples of the upper reference limit (URL) for each of these liver-function tests, setting the URL high enough to overcome method- and age-related differences. Graphs of "first test" data from 141 patients show the great sensitivity of the two aminotransferase assays for Reye's syndrome: only 2% of the results fall below their URL, whereas about 32% of NH3 determinations and 27% of prothrombin times fall below their URL. Thus measuring the aminotransferases apparently is at least 10 times more useful than the other three analytes as "first tests." Current record keeping does not provide a ready means for assessing the specificity of these tests to determine the number of false positives, but does provide useful data for assessing sensitivity and false negatives.

Studies on the quality of specimens obtained by skin-puncture of children. 2. An analysis of blood-collecting practices in a pediatric hospital.

We quantified blood-collecting practices for chemistry in a pediatric hospital. Skin-puncture provided 67% of samples, and in-dwelling catheters (lines), 31%. About 46% of samples collected (day-shift) were urgent ("stats"). A single skin-puncture provided 448 microL (range, 150-1350) of blood, and 80% of requests, but only 58% of stats. About 1.3 punctures per request were required. Time spent collecting blood was 11.0 min per single request. Patients undergoing total parenteral nutrition took 17.9 min and 3.6 skin-punctures per request. Analytical time for stat blood gases was about 6 min, total ("turnaround") time, about 16 min. Turnaround time for stat requests involving the Ektachem 400TM instrument was 32.4 min; for non-stat, at least 56 min. Other tests required 151 min. Blood gases and electrolytes represented the majority of all tests ordered, and 97% of in-dwelling line blood-draws. There was no correlation between age and number of tests per request, but the youngest patients (0 to 1 year) had more skin-punctures per request (1.4), along with the greatest number (55.5%) and frequency of tests.

Studies on the quality of specimens obtained by skin puncture of children 1. Tendency to hemolysis, and hemoglobin and tissue fluid as contaminants.

When preferred skin-puncture and blood-collecting techniques were used, the mean artifactually produced hemoglobin in 417 samples of plasma from pediatric patients was 260 mg/L. Highest values occurred exclusively in newborns, 0 to 13 days old (n = 176; mean, 390 mg/L), one-third of whom were premature. The highest value was 1470 mg/L. Only 3% of the samples exceeded 1000 mg/L. After 13 days, technically produced hemolysis is about the same as that for adult plasma (less than 200 mg/L). When skin-puncture and blood-collecting techniques are faulty--e.g., from excessive squeezing at the puncture site--plasma K and hemoglobin may be increased in the newborn to 13-day-old infant, and occasionally in older subjects. By determining plasma hemoglobin, K, blood hemoglobin, and hematocrit the contribution of "tissue fluid" is readily calculated. With excessive squeezing at the sampling site, tissue fluid sometimes contaminates plasma with hemoglobin and K, particularly in the youngest group. Values for alanine and aspartate aminotransferases, lactate dehydrogenase, inorganic P, and Na were little altered, even with squeezing, a fact particularly surprising for the enzymes, which are known to be present in markedly higher concentrations in erythrocytes and other tissues. Our data validate the Elson--Ivor--Gochman method (Am. J. Clin. Pathol. 69: 354-355, 1978) for quantitation of hemoglobin in plasma.

Preservation, distribution, and assay of glucose in blood, with special reference to the newborn.

Of several preservatives we tested, a mixture of "isotonic" sodium fluoride and sodium iodoacetate (17.7 and 5.0 g/L, respectively) best inhibits glucose loss from blood collected from the newborn. However, the inhibition is incomplete. Twenty microliters of blood is diluted with 100 microliter of preserving solution. After centrifugation, the glucose in 100 microliter of prewarmed supernate (diluted plasma) is measured in a Beckman Glucose Analyzer, based on the action of a glucose reagent and the rate of oxygen consumption. The method, in effect, determines the glucose in whole blood, except for about 5% of the total that remains in the erythrocytes. Glucose is distributed in blood according to the water content of cells and plasma. From concentrations found in cells and plasma, we can calculate the value for glucose in whole blood with an accuracy of 95.2%. The modified method we describe shows acceptable precision, as judged from within-run and day-to-day CV--generally well below 5% for each.