Clinical Chemistry and Biochemical Tests

Clinical Chemistry and Biochemical Tests

• Biochemical tests are used extensively in medicine for diagnosis, prognosis, monitoring, and screening.
• The results of biochemical tests are useful to clinicians in making a differential diagnosis, confirming or rejecting a diagnosis, and predicting the course of a disease.

Diagnosis and Prognosis

• Diagnosis is the art of distinguishing one disease from another based on a patient's history and examination findings.
• Biochemical and other investigations are used to distinguish between diseases with similar clinical pictures.
• Tests may be selected to confirm or disprove a diagnosis, and biochemical tests are important for confirming or rejecting a clinical diagnosis.
• Prognosis is a doctor's prediction of how a patient's disease will progress, based on knowledge of the disease's course in other patients and the patient's general health, age, and sex.
• Tests used primarily for diagnosis may also provide prognostic information, such as serial measurements of plasma creatinine concentration in progressive renal disease.

Monitoring and Screening

• Monitoring involves sequential recording of a patient's condition to follow the course of an illness and monitor the effects of treatment.
• Biochemical tests may be used to detect complications of treatment, such as hypokalemia during diuretic treatment.
• Screening involves detecting individuals affected with a condition before it becomes clinically apparent, such as mass screening of newborn babies for phenylketonuria (PKU) and congenital hypothyroidism.

Categories of Clinical Chemistry Tests

• Core biochemistry tests: commonly requested tests of value in many patients, carried out in every biochemistry laboratory (e.g. sodium, potassium, chloride, urea, creatinine, calcium, phosphate, etc.).
• Specialized tests: less commonly asked tests that may be referred to larger laboratories (e.g. DNA analysis).
• Urgent tests: tests processed rapidly in emergency laboratories, such as those needed for immediate treatment decisions.

Specimen Collection and Identification

• Blood may be obtained from veins, arteries, or capillaries, with venous blood being the specimen of choice.
• Skin puncture may be used to obtain a small volume of blood for a blood test, especially in infants.
• Whole blood, plasma, or serum can be used for testing, each requiring specific collection and preparation procedures.
• Specimen identification is critical, with errors in labeling or identification being a common source of erroneous lab results.

Biological Factors Affecting Test Results

• Sex of the patient: e.g. lower blood hemoglobin concentrations in women, affecting serum bilirubin concentrations.
• Age of the patient: e.g. bilirubin levels in infants, low blood glucose concentrations in newborns.
• Diet: e.g. vegetarianism affecting LDL and VLDL concentrations, total lipid and phospholipid concentrations.
• Time of sample collection: e.g. cortisol levels.
• Posture of the patient: e.g. supine vs. sitting or standing, affecting certain test results.
• Medical history, pregnancy, drug history, and smoking can all affect test results.

Accuracy and Precision

• Accuracy refers to the proximity of a measurement to the true value.
• Precision refers to the repeatability or reproducibility of a measurement.
• A measurement can be precise but not accurate due to bias in the test method.
• Control specimens are used to ensure the accuracy and precision of laboratory tests.

This quiz covers the role of biochemical tests in medicine, including diagnosis, prognosis, and monitoring. Learn how clinicians use test results to make informed decisions.