Clinical Biochemistry in Medical Diagnostics

Biochemistry (clinical chemistry)

Biochemistry (clinical chemistry) also known as chemical pathology, is the area of chemistry that is generally concerned with analysis of bodily fluids for diagnostic and therapeutic purposes (not to be confused with medicinal chemistry, which involves basic research for drug development). In other word, Clinical biochemistry refers to the analysis of the blood plasma (or serum) for a wide variety of substances substrates, enzymes, hormones, etc and their use in diagnosis and monitoring of disease.

. Analysis of other body fluids (eg, urine, ascitic fluids, CSF) is also included. The discipline originated in the late 19th century with the use of simple chemical reaction tests for various components of blood and urine. In the many decades since, other techniques have been applied as science and technology have advanced, including the use and measurement of enzyme activities, spectrophotometry, electrophoresis, and immunoassay. There are now many blood tests and clinical urine tests with extensive diagnostic capabilities.

Most current laboratories are now highly automated to accommodate the high workload typical of a hospital laboratory. Tests performed are closely monitored and quality controlled. All biochemical tests come under chemical pathology. These are performed on any kind of body fluid, but mostly on serum or plasma. The type of test required dictates what type of sample is used. A large medical laboratory will accept samples for up to about 700 different kinds of tests. Even the largest of laboratories rarely do all these tests themselves, and some must be referred to other labs.

This large array of tests can be categorised into sub-specialities of: General or routine chemistry commonly ordered blood chemistries (e.g., liver and kidney function tests). Special chemistry - elaborate techniques such as electrophoresis, and manual testing methods. Clinical endocrinology the study of hormones, and diagnosis of endocrine disorders. Toxicology the study of drugs of abuse and other chemicals. Therapeutic Drug Monitoring measurement of therapeutic medication levels to optimize dosage. Urinalysis chemical analysis of urine for a wide array of diseases, along with other fluids such as CSF and effusions Fecal analysis mostly for detection of gastrointestinal disorders.

Common clinical chemistry tests include: Electrolytes Electrolytes are present in the human body, and the balance of the electrolytes in our bodies is essential for normal function of our cells and our organs. Common electrolytes that are measured by doctors with blood testing include: Sodium level: increases due to Conn syndrome (hyperaldosteronism), restricted water intake, vomiting, and most causes of dehydration. It decreases due to hypoadrenocorticism, loss of any high-sodium fluid such as some forms of renal disease, and insufficient sodium provision during IV fluid therapy. Potassium level: increases due to hypoadrenocorticism and severe renal failure (especially terminal cases). It decreases due to Conn syndrome, chronic renal dysfunction, vomiting, diarrhea, and insufficient potassium provision during IV fluid therapy. Chloride level: increases in acidosis, and in parallel with increases in sodium concentration. It decreases in alkalosis, vomiting (especially after eating), and in association with hyponatremia.

Bicarbonate level: increases in metabolic alkalosis and decreases in metabolic acidosis. It is less useful to assess respiratory acid/base disturbances. Calciumlevel: increases due to dehydration (which is also associated with increased albumin), primary hyperparathyroidism (neoplasia of parathyroid gland), primary pseudohyperparathyroidism parathormone-related peptide [PRP], usually perianal adenocarcinoma or some form of lymphosarcoma), bone invasion of malignant neoplasms, thyrotoxicosis (uncommon), and overtreatment of parturient paresis. It decreases due to hypoalbuminemia, parturient paresis, oxalate poisoning, chronic renal failure (secondary renal hyperparathyroidism), acute pancreatitis (occasionally), surgical interference with parathyroid glands, hypoparathyroidism. (neoplasms producing and idiopathic (autoimmune) Magnesiumlevel: increases are rarely seen, including during acute renal failure. It decreases in ruminants due to dietary deficiency, either acute or chronic, and diarrhea (uncommon). Phosphate

Renal (Kidney) Function Tests Healthy kidneys remove wastes and excess fluid from the blood. Blood and urine tests show how well the kidneys are doing their job and how quickly body wastes are being removed. Urine tests can also detect whether the kidneys are leaking abnormal amounts of protein, a sign of kidney damage.

Here's a quick guide to the tests used to measure kidney function. Creatinine level: Creatinine is a waste product that comes from the normal wear and tear on muscles of the body. Creatinine levels in the blood can vary depending on age, race and body size. A creatinine level of greater than 1.2 for women and greater than 1.4 for men may be an early sign that the kidneys are not working properly. It increases due to renal dysfunction, blocked urethra, and ruptured bladder. It decreases due to sample deterioration. Animals with a high muscle mass have high-normal creatinine concentrations, whereas animals with a low muscle mass have low-normal creatinine concentrations. Creatinine measurement is used especially for renal disease.

Blood urea level: Urea nitrogen comes from the breakdown of protein in the foods you eat. A normal BUN level is between 7 and 20. It increases due to excess dietary protein, poor quality dietary protein, carbohydrate deficiency, catabolic states, dehydration, congestive heart failure, renal failure, blocked urethra, and ruptured bladder. It decreases due to low dietary protein, gross sepsis, anabolic hormonal effects, liver failure, portosystemic shunts (congenital or acquired), and inborn errors of urea cycle metabolism. Urea measurement is used especially to indicate renal disease and to a lesser extent liver dysfunction.

Glomerular Filtration Rate (GFR): This test is a measure of how well the kidneys are removing wastes and excess fluid from the blood. It is calculated from the serum creatinine level using age and gender with adjustment for those of African American descent. Normal GFR can vary according to age (as you get older it can decrease). The normal value for GFR is 90 or above. A GFR below 60 is a sign that the kidneys are not working properly. Once the GFR decreases below 15, one is at high risk for needing treatment for kidney failure, such as dialysis or a kidney transplant.

The most commonly used formula is the "4-variable MDRD," which estimates GFR using four variables: serum creatinine, age, ethnicity, and gender. The original MDRD used six variables with the additional variables being the blood urea nitrogen and albumin levels. The equations have been validated in patients with chronic kidney disease; however, both versions underestimate the GFR in healthy patients with GFRs over 60 mL/min. The equations have not been validated in acute renal failure. For creatinine in mol/L: eGFR= 32788 x S.Cr-1.154 x Age-0.203 x (1.21^0 if Black) x (0.742 if female) For creatinine in mg/dL: eGFR= 186 x S.Cr-1.154 x Age-0.203 x (1.21^0 if Black) x (0.742 if female)

Creatinine levels in mol/L can be converted to mg/dL by dividing them by 88.4. The 32788 number above is equal to 186 88.41.154. A more elaborate version of the MDRD equation also includes serum albumin and blood urea nitrogen (BUN) levels: eGFR= 170 x S. Cr-0.999 x Age-0.176 x (0.762 if female) x (1.180 if Black) x BUN-0.170 x Albumin+0.318 where the creatinine and blood urea nitrogen concentrations are both in mg/dL. The albumin concentration is in g/dL. These MDRD equations are to be used only if the laboratory has NOT calibrated its serum creatinine measurements to isotope dilution mass spectrometry (IDMS). When IDMS-calibrated serum creatinine is used (which is about 6% lower), the above equations should be multiplied by 175/186 or by 0.94086.

Liver Function Tests Liver helps the body to digest food, store energy, and remove poisons. Liver function tests are blood tests that check to see how well the liver is working. They check for liver damage, and can help diagnose liver diseases such as hepatitis and cirrhosis. Liver function tests can be done as part of a regular checkup, or if there are symptoms of liver disease. It also used to monitor some liver diseases, treatments, and possible side effects of medicines.

Liver function tests measure certain proteins, enzymes, and substances, including: Total protein level: increases due to dehydration, chronic inflammation, and paraproteinemia. It decreases due to overhydration, severe congestive heart failure (with edema), protein-losing nephropathy, hemorrhage, burns, dietary protein deficiency, malabsorption, and some viral conditions (especially in horses). Albumin level: increases due to dehydration. It decreases due to the same factors as total protein, plus liver failure.

Bilirubin; direct; indirect; total Bilirubin level increases due to fasting (benign effect in horses and squirrel monkeys, may be caused by hepatic lipidosis in cats), hemolytic disease (usually mild increase), liver dysfunction, and biliary obstruction (intra- or extrahepatic). Theoretically, hemolysis is characterized by an increase in unconjugated (indirect) bilirubin, whereas hepatic and post-hepatic disorders are characterized by an increase in conjugated (direct) bilirubin; however, in practice this differentiation is unsatisfactory. Better appreciation of the source of the jaundice is gained from bile acid measurements.