It is impossible comprehensively to review the growing literature on the ‘laboratory neurowork-up’ of individuals with child neuropsychiatric disorders in a brief chapter. The following presentation instead includes some clinical guidelines in respect of why and how to use the available laboratory examinations in the workup of individuals with neuropsychiatric disorders with childhood or adolescent onset.

Neurochemistry, molecular genetics and cytogenetics

Only a few years ago, it was still possible to treat neurochemistry, cytogenetics and molecular genetics as separate. Today, such subdivision is no longer possible. Neurotransmitters, neuromodulators, enzymes, other proteins, ions, vitamins and co-factors are all part of ‘neurochemistry’ and the intricate interplay of neural and glial structures in the central nervous system. Most of them (and their sites of action) are ruled by specific genes. Abnormalities of these genes can now often be detected at the molecular level. Sometimes the gene abnormalities engage portions of the genome large enough to allow visualization in the light microscope and the deviation then becomes classifiable as ‘cytogenetic’.

There is no way in which a laboratory work-up of the individual patient with neuropsychiatric disorder could be performed without the guidance of the differential diagnostic considerations. In other words, there is no neurochemical, blood, urine or CSF test that should be performed in all patients presenting with neuropsychiatric symptoms. The clinician will have to consult the chapters on specific disorders for detailed instructions.

Nevertheless, a few basic guidelines can be provided here.