This book incorporates a wide variety of clinical conditions requiring admission to the intensive care unit that necessitate timely performance of diagnostic tests and their correct interpretation to guide the best treatment. It tries to translate complex physiological principles and diagnostic algorithms into a clinically relevant format that can be easily understood by clinicians. It also explains at length the key clinical inputs to be acquired by laboratory physicians before reporting the results and tries to solve the common dilemmas leading to misinterpretation. The importance of every detail, from sample collection and dispatch to correlation of clinical state report, has been adequately explained with suitable examples and proper explanations.