Laboratory Evalualtion of EM in a Neonate
The laboratory evaluation for a newborn suspected of having an EM can be illustrated as a pyramid in Fig 1. The specific details of collection, handling, processing, and shipping, if needed, of laboratory samples must be clearly understood before the samples are obtained. In addition, during this time period, frequent communication and collaboration with laboratory personnel in more than one laboratory may be needed. This will expedite testing and avoid needless delay and repetition of sample collection and processing from an already compromised newborn. The first tier includes broadly focused screening tests that can provide a relatively rapid and inexpensive diagnostic evaluation. Several of these tests are routinely performed during the care of a sick newborn. A significant imbalance may be identified, which when promptly treated may prevent long-term sequelae. Additional tests for metabolic disease are listed in tier 2. Tier 2 tests of the pyramid provide more information as to differential diagnosis. The studies in tier 1 and 2, when combined, can help direct care of the patient and the need for consultation with a regional medical center where clinical biochemical ge-netics/metabolic disease expertise is available. Tier 3 of the pyramid focuses on the metabolic disease process and provides information for consultation with the metabolic disease specialist. These tests are not routinely available in many local hospital laboratories. As these studies require highly specialized laboratory skills and equipment, these tests are generally available at larger, regional medical centers. In addition, some commercial laboratories also offer these tests. Many of the commercial laboratories, with some notable exceptions, cannot provide STAT analyses and/or expert result interpretation. It can be difficult to interpret results of laboratory tests performed at commercial laboratories where the techniques used can be different from academic laboratories, though recently the quality of testing offered by several commercial laboratories has improved greatly. The fourth tier of the pyramid involves highly specialized tests in the diagnosis of EM. Definitive diagnostic testing can require specific enzymatic analysis using white blood cells, cultured skin fibroblasts, or other tissue specimen, such as muscle. Only a few laboratories perform many of the enzyme and mutation analyses that are required for confirmation of the diagnosis. The results may not be available immediately, but can take days, weeks, or months to be reported by the specific biochemical genetic laboratory. The metabolic disease consultants can assist in identifying which specific tests to order, the priority of the tests, and can provide direction in the initial treatment of the neonate.
Pyramid of laboratory tests for suspected metabolic disease in a newborn.
NAINR. 2003;3(4) © 2003 W.B. Saunders
Cite this: Not So Rare: Errors of Metabolism During the Neonatal Period - Medscape - Dec 01, 2003.