What is clinical biochemistry?
Blood carries a history of its interactions with both physiologic and disease processes. The balance of chemical reactions makes possible homeostasis, the stable equilibrium that defines health. Blood tests can identify abnormal processes that jeopardize homeostasis, from the specific imbalance among electrolytes to the pH (acidity) of the blood that is the end-result of illness.
Tests for Identifying Parameters of Health vs. Illness
The Metabolic Profile: When speaking of clinical biochemistry, the starting point is the metabolic profile, which tests an entire battery of physiologic functions specific to different organs by measuring the amounts of individual products from these organs.
- Blood urea nitrogen (BUN): BUN is a waste product of protein metabolism, and its excretion falls with kidney disease, raising its level in the blood. It is also sensitive to dehydration.
- Creatinine: A waste product of muscle metabolism, which accumulates when the kidneys fail to excrete them in kidney disease.
- BUN/creatinine ratio: An elevated ratio > 20:1 indicates decrease in kidney function.
- Calcium: elevations indicate kidney dysfunction and predict those at risk for kidney stones.
- Sodium, potassium, chloride: Electrolytes whose balance is maintained by normal kidney function. Elevations indicate kidney disease.
- Albumin: protein made by the liver and documents liver function.
- Alkaline phosphatase (ALP), Alanine aminotransferase (ALT), and Aspartate aminotransferase (AST): biomarkers elevated with liver disease.
- Total protein: Mainly, globulin and albumin.
- Bilirubin: rises with obstruction in the biliary tract or in primary liver failure, such as cirrhosis.
- Glucose rises when insulin falls, as it does absolutely in Type 1 DM and relatively in Type 2 DM. It is also a measure for how effectively the kidney excretes excess glucose in the blood.
Other Biochemical Tests: as adjuncts to the metabolic profile, other tests can delve more specifically into directions indicated by the metabolic profile results.
- Blood gases, drawn from an artery, give a picture as to how well the blood is being oxygenated and how well carbon dioxide is being removed. This is a part of the normal acid-base balance of the body, and both biochemical processes and respiration can drive the acid concentration (pH) up or down, which complicates further the illnesses that create the abnormal pH, because biochemical reactions need a normal pH in which to function, including the healing reactions.
- Cardiac enzymes are useful in identifying biomarkers released from damaged heart tissue, used to diagnose cardiac events such as ischemia and infarction.
- Immunological tests, such as CRP (C-reactive protein) and ESR (erythrocyte sedimentation rate) for inflammation, rheumatoid factor (RA factor), anti-nuclear antibodies (ANA) and other immunological biomarkers, can be used as part of a diagnostic work-up for specific immunologic diseases.
- Clotting studies can identify D-dimers, part of the diagnostic approach to coagulation problems. The INR is also a reflection of clotting used to titrate anticoagulation therapy in thromboembolic disease. Hemoglobin A1c, for monitoring diabetics.
- Lipid profiles measure cholesterol and triglycerides, which when elevated, risk cardiovascular disease.
Electrophoresis is a technique for separating out different components of one thing, for example, the types of hemoglobin a person may have, important in such diseases as sickle-cell anemia.