Chapter 1: Introduction
1.1 Aims:
i. To give a possible diagnosis of the patient's health status using the urea and creatinine results from the renal function test.
ii. To identify the possible interferences that could affect the accuracy of the manual method.
iii. To list the possible pre-analytical variation that could affect the measurement of urea and creatinine.
1.2 Background Information
The determination of blood urea nitrogen (BUN) is a common method used by the laboratory to evaluate the function of kidney. Measurements of urea nitrogen are usually used in conjunction with the creatinine test for diagnosis and treatment of certain renal and metabolic disorders. These tests provide a differential diagnosis of
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BUN test
In the Blood Urea Nitrogen (BUN) test, lab personnel check for the decrease in absorbance at 340 nM using a photo spectrometer when NADH is dissociated during the reaction between ammonia and alpha-ketoglutaric acid. As the concentration of the Urea in a specimen increases, the rate of decrease in absorbance gets higher
1.4. Creatinine test
In the creatinine test, creatinine forms a yellow-orange complex with picrate in an alkaline solution. The colour intensity is directly proportional to the concentration of creatinine in the patient's specimen. The colour intensity is measured using the photo spectrometer at 505nm. To date, this method in which creatinine is treated with an alkaline picrate solution to produce a yellow-orange complex, is still the most commonly used method for measuring creatinine. This test however, is nonspecific and subject to interference with many non-creatinine chromogens. The test is also sensitive to pH and temperature
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Standard solution
The standard solution was tested for its value and was used in the calculation of the patient's urea and creatinine value.
ii. Running patient's specimen
a. Creatinine
1ml of creatinine reagent 1 and 200ml of creatinine reagent 2 was pipetted into the same 1ml cuvette. Following that, 40ml of patient's sample was transferred into the cuvette. The absorbance of the mixture was measured at 30s (A1), 5min and 6min intervals. The value A2 was obtained by averaging the values of the 5th and 6th minute.
b. Urea
750 ml of urea reagent 1 and 450ml of urea reagent 2 was pipetted into the same 1ml cuvette. Following that, 12ml of patient's sample was transferred into the cuvette. The absorbance of the mixture was measured at 30s (A1), 5min and 6min intervals. The value A2 was obtained by averaging the values of the 5th and 6th minute.
iii. Calculation
(A1-A2)sample/control
Urea concentration = 15.4 mmol/L X (A1-A2)standard
Creatinine concentration = 313 mmol/L X (A2-A1)sample/control