22. Urea - common data for the parameter, principles of the analytical methods, source of errors, indications for investigation, patient preparation, reference ranges, interpretation of results.

Urea - common data for the parameter, principles of the analytical methods, source of errors, indications for investigation, patient preparation, reference ranges, result’s interpretation.

Urea includes nearly half the nitrogen of the non-protein nitrogen fraction. Urea serves an important role in the metabolism of nitrogen-containing compounds and is the main nitrogen containing substance in the urine of mammals. Urea is a by- product from metabolism of proteins by the liver, and therefore removed from the blood by the kidneys. The liver produces urea in the urea cycle as a waste product of the digestion of protein. Urea itself is not toxic. Being practically neutral and highly soluble in water, urea is a safe way for the body to transport and excrete excess nitrogen. Urea if filtered in the glomerulus. About 40% of it is reabsorbed in the renal tubules. Most of the urea is excreted in the urine and small amounts – through the gastrointestinal tract and the skin. The blood urea nitrogen test is a measure of the amount of nitrogen in the blood in the form of urea, and a measurement of renal function.

Principles of the analytical methods: colorimetric; enzymatic (urease) methods– high analytical reliability

Sources of error: urease is suppressed by the presence of heavy metals (Hg,Cu etc. – clear laboratory vessels); interference is caused by haemolysis, lipemia and endogenous ammonia and drugs.

indications for investigation: non-clarified comas, post-surgery control, patients on haemodialysis, patients with acute and chronic renal failure (ARF and CRF), control of food protein intake in patients with CRF. Urea is not an adequate indicator for the early diagnosis of renal diseases.

Patient preparation – in accordance with the requirements for obtaining specimens for investigation

1. Blood, urine and other samples for examination are collected between 7-9 a.m. in the morning
2. Stop taking drugs (if possible).
3. Physical and psychological rest of the patient before and during the examination (procedure)
4. If possible, blood must be collected in a seated position of the patient, 15-20 min after seating. Hands should not hang down.
5. Strict observation of procedures of venipuncture, urine collection and collection of other biological samples.

Reference ranges: serum male 3,2 - 8,2 mmol/l, female 2,6 - 7,2 mmol/l

Results interpretation: Uraemia – high levels of urea in the serum – above 50 mmol/l. Azotaemia is a medical condition characterized by abnormally high levels of nitrogen-containing compounds, such as urea, creatinine, various body waste compounds.

High values:

1. Prerenal causes: congestive heart failure, shock, haemorrhage