Introduction (general information about analyte, sample)
Principles of the determination
Clinical signification
Risk factors
Effects of drugs (analytical drugs interference)
Findings (interpretation of results)

 Alkaline phosphatase (AP)
Alkaline phosphatases are group-specific enzymes that catalyze hydrolysis of the phosphate acid and alcohol monoesters. Optimal pH for the enzyme activity is between 9.8 and 10.5, and depends on the substrate and buffer used.
The enzyme is most abundant in the small intestine epithelium, renal tubules, bone, liver, placenta and leukocytes. Alkaline phosphatase (AP) found in serum of healthy adults mostly originates from the liver, and in children's serum also from bone. The presence of various diseases involving these organs leads to an increase in the catalytic concentration of AP in serum.

 γ-Glutamyl transferase (γ-GT)
Gamma-glutamyltransferase (g-GT) is an enzyme catalyzing the residual hydrolysis-released glutamic acid to some amino acid or peptide. In the human body, it is mostly bound to cell membranes, and is predominantly found in the epithelial cell brush border of proximal renal tubules, prostate, pancreas, liver, small intestine epithelium, and brain.
The increase in the catalytic concentration of g-GT is the most sensitive indicator of liver damage, and is especially pronounced in case of alcohol induced liver lesions. Also, g-GT is a valuable parameter in the differential diagnosis of hepatocellular and obstructive jaundice.

 Aminotransferases (Transaminases)
Transaminases or aminotransferases are the enzymes involved in amino group transfer from amino acid to ketoacid, whereby a new amino acid and a new ketoacid are formed. Pyridoxal phosphate participates in the reaction as a coenzyme. Determination of the catalytic activities of these enzymes is important in the diagnosis of liver diseases and myocardial infarction as well as in the differential diagnosis of diseases of the liver, pancreas and some other disorders.

 α- Amylase
a-Amylase is an enzyme of low molecular mass (45000 to 50000). According to the site of action, it is a digestive juice enzyme. Determination of the catalytic concentration of a-amylase is used in the diagnosis and follow-up of therapeutic success in acute pancreatitis, and for detection of salivary gland inflammation.

 Bilirubin
Bilirubin is a breakdown end product of heme containing proteins. About 80% of bilirubin are formed from the degradation of erythrocyte hemoglobin (after 120 days of erythrocyte life in the blood) in the reticuloendothelial system (RES). The remaining 20% of daily produced bilirubin are formed from erythrocyte precursors in bone marrow (inefficient erythropoiesis) and other heme proteins (myoglobin, cytochromes, catalase).
Determination of bilirubin is of great importance in the differential diagnosis of jaundice.

 Urea
Urea is the major metabolic product of nitrogen substances in the body. It is formed in the liver via Krebs-Henseleit (urea) cycle from ammonia. Urea is freely filtered through the glomeruli, and 40% - 50% of urea are passively reabsorbed in proximal tubules.
The concentration of urea used to be simply expressed as such, i.e. as urea concentration, whereas now it is mostly expressed as the concentration of N-urea, i.e. blood urea nitrogen (BUN).

 Creatinine
Creatine and creatinine are metabolized in the kidneys, muscle, liver and pancreas.
Structurally, creatine is a methylguanidinoacetic acid which makes up to 98% of total muscle mass and plays a crucial role in muscle contraction. Creatine is excreted in the form of anhydride, i.e. creatinine.
Serum creatine concentration is increased in muscular atrophy and muscular dystrophy, and following extremity amputation. Excessive proteinuria results from impaired tubular creatine reabsorption. Determination of creatinuria has a diagnostic value only in case of atrophy and in muscle regeneration in myopathies.

 Creatinine clearance
Renal clearance is a measure of kidney functional capacity. Clearance is the number of milliliters of plasma 'purified' from a substance per second.
Creatinine determination in serum and urine provides useful diagnostic information for the assessment of kidney function.

 Uric acid (urate)
Uric acid is the end product of the metabolism of exogenous and endogenous purines. In humans, uric acid is excreted as the metabolic end product of purines. Uric acid is mostly eliminated from the circulation by urine (about 75%), and about 25% are secreted to the intestines, where it is degraded by intestinal bacteria.

 Lipids
The most important lipids present in blood plasma include fatty acids, triglycerides, cholesterol, phospholipids and steroid hormones.
Assessment of lipid metabolism impairments is based on plasma concentrations of cholesterol and triglycerides, and on data obtained by lipoprotein electrophoresis. Disorders due to lipid metabolism impairments are associated with a high risk of atherosclerosis.

 Total protein
Proteins are constitutional material of the human body. Proteins are very different but specific for particular organs and tissues.
They are composed of amino acids linked with peptide bonds. Proteins characteristically contain nitrogen at a constant ratio of about 16% of total protein. According to their composition, proteins are classified into simple and complex proteins. Simple proteins are composed exclusively of amino acids, whereas complex proteins contain so-called non-protein or prosthetic group in addition to their protein structure. Proteins have been named according to their prosthetic groups, e.g., glucoproteins, lipoproteins, hemoproteins, etc.

 Glucose
Carbohydrates are compounds consisting of carbon, oxygen and hydrogen, with a hydrogen to oxygen ratio identical to that found in water (H:O = 2:1).
Carbohydrates are divided into simple sugars or monosaccharides (e.g., glucose, galactose, fructose) and complex sugars, i.e. oligosaccharides or polysaccharides (e.g., glycogen, starch). Carbohydrates are mostly of vegetable origin, and are the main source of energy for the human body. The body utilizes the energy derived from carbohydrates for cell growth, other metabolic processes, and biosynthesis of new substances.

 Glucose tolerance test
Oral glucose load test (oral glucose tolerance test, OGTT)
The diagnosis of diabetes mellitus or other carbohydrate metabolism impairment is verified by classical oral glucose tolerance test (OGTT) (Table). OGTT determines the state of carbohydrate metabolism and is used to recognize an early stage of diabetes mellitus. Upon glucose load, the concentration of glucose rises; OGTT determines the time needed for the concentration of glucose to return to normal. This test simulates the physiologic intake of food under standard conditions.

 Electrolytes
Electrolytes are involved in the following processes:
they maintain the balance and distribution of water, they maintain normal osmotic pressure and hydration, they provide support to the work of the heart and other muscles, they are enzyme activators, etc.
The main extracellular fluid cations are potassium, sodium, calcium and magnesium, while the main anions are chlorine, bicarbonates, phosphate, sulfate, organic acid and protein.

 Oligoelements
Oligoelements are also known as elements in traces or elements found in amounts lower than 0.01% of total body mass.
However, some oligoelements are indispensable for normal life of the body (e.g., iron, copper, zinc, manganese). High concentrations of abnormal (non-essential) oligoelements (e.g., cadmium, lead, mercury, etc.) are toxic for humans.