Newborn screening test by MS/MS method is designed for 34 primary metabolic diseases and during this test about 24 other diseases may be detected secondarily. Unfortunately, this method is not able to identify all cases of metabolic diseases, which include more than 700 types, and includes only common and treatable cases. At the same time, even these common cases, if they are of a mild type, may not be detected in the screening test. In some cases, the positive results in the newborn screening test may not be due to metabolic disease and may be related to environmental or delivery causes that cause false positive results in the test.
Therefore, for the second stage, additional tests have been designed to confirm, diagnose or reject suspicious cases, which include the examination of blood amino acids by HPLC method - plasma acylcarnitines by LC-MS/MS method - amino acid chromatography, and urine sugar - examination of urine organic acids by GC-MS method and other tests such as sugar, blood acid, ammonia, lactate and pyruvate, liver and kidney tests, urine ketone, etc. In some cases, it may be necessary to perform third-stage tests such as cerebrospinalfluid examination or invasive tests such as liver skin or muscle biopsy for enzyme tests.
Performing additional tests not only in cases where the screening test is positive but also in other cases where the screening test is normal but there are signs of metabolic diseases such as developmental delay, unexplained seizures, muscle weakness, enlarged liver and spleen, frequent vomiting, hypoglycemia, It is necessary if there is an increase in blood acid or ammonia, etc.
Finally, based on the results of these tests, the treating doctor can determine the type of disease and requests a genetic test related to the disease to definitively diagnose and confirm the disease; which is a prerequisite and necessary test to perform prenatal tests, and without doing it, there will be no possibility of amniocentesis and prevention of the birth of an affected child.
Unfortunately, in many cases, there is no specific biomarker for the definitive diagnosis of the disease, and it may be recommended to perform extensive genetic tests such as Whole Exome Sequencing (WES) using the Next Generation Sequencing (NGS) method for definitive diagnosis of the disease.
It should be noted that the selection of the type of supplementary test is the responsibility of the metabolic specialist because depending on the type of possible disease, different tests can be avoided by limiting them from doing unnecessary things that are often expensive and time-consuming.