Laboratory tests may be recommended when a doctor needs additional information to diagnose a condition, investigate symptoms, monitor an existing disease or assess how the body is responding to treatment. Blood and urine tests are commonly used to evaluate organ function, blood counts, hormones, glucose and signs of infection or inflammation. Tissue samples may be examined when a biopsy is needed to investigate an abnormal area. The type of sample and test depend on the patient's symptoms and the clinical question being investigated.

Pathology can provide microscopic information that cannot always be obtained through symptoms, physical examination or imaging alone. When tissue or cells are collected through a biopsy or other procedure, a pathologist examines the sample for changes that may indicate cancer, infection, inflammation or another disease. Specialized laboratory techniques can provide additional information about the characteristics of abnormal cells. Pathology findings are interpreted alongside the patient's clinical history and other investigations to help establish an accurate diagnosis and guide treatment.

Microbiology testing can help identify infections caused by bacteria, viruses, fungi and parasites. Depending on the suspected infection, samples may be collected from blood, urine, respiratory secretions, stool, wounds or other body sites. Laboratory methods can identify the microorganism responsible and, in some cases, determine which medicines are likely to be effective against it. The choice of test depends on the symptoms, suspected source of infection and clinical circumstances.

Laboratory results provide objective information that can help doctors confirm a diagnosis, determine disease severity and select appropriate treatment. For infections, microbiology testing may identify the organism causing the infection and, when appropriate, provide information about antimicrobial susceptibility. Pathology results can help determine the type and characteristics of a tumour or other tissue abnormality. Laboratory tests may also be repeated during treatment to monitor response, detect complications or determine whether therapy needs to be adjusted.

Preparation depends on the specific test. Some blood tests may require fasting, while others do not. Certain urine, stool or other specimen tests require specific collection methods or timing to ensure an accurate result. Patients should tell their healthcare provider about medicines, supplements and relevant medical conditions, as some tests can be affected by these factors. Do not stop prescribed medicines unless instructed to do so. Always follow the preparation and specimen-collection instructions provided by your healthcare team or laboratory.

Laboratory results can influence important decisions throughout a patient's care, from identifying a disease to selecting treatment and monitoring recovery. Accurate testing helps reduce the risk of missed or incorrect diagnoses, inappropriate treatment and unnecessary investigations. Reliable sample collection, appropriate test selection, quality laboratory processes and careful interpretation are all important for dependable results. Laboratory findings are not considered in isolation; clinicians interpret them alongside symptoms, examination findings, medical history and other investigations to make informed decisions about patient care.