The purpose of this book is to help nurses, midwives and health professionals to better understand how the work of clinical laboratories contributes to patient care. It answers the following questions: * Why is this test being ordered on my patient? * What sort of sample is required? * How is that sample obtained? And most importantly: * What is the significance of the test result for my patient? Retaining its accessible and user-friendly style, the aim of this book remains the same: to provide nurses with as much relevant information as possible about the most commonly requested laboratory rests. This is not a book about laboratory technique - its focus is on the clinical significance of test results, and therefore the patient. The third edition is more comprehensive in terms of the number of tests discussed, incorporates colour to aid the accessibility, and includes more paediatric content.