Tiêu đề 13. RENAL & THYROID FUNCTION TESTS.pdf ✅

PHARMD GURU Page 1 RENAL FUNCTION TESTS INTRODUCTION:  Renal function may be assessed by measuring blood urea nitrogen (BUN) and serum creatinine. Renal function decreases with age, which must be taken into account when interpreting test values. a) These tests primarily evaluate glomerular function by assessing the glomerular filtration rate (GFR). b) In many renal diseases, urea and creatinine accumulate in the blood because they are not excreted properly. c) These tests also aid in determining drug dosage for drugs excreted through the kidneys.  Azotaemia describes excessive retention of nitrogenous waste products (BUN and creatinine) in the blood. The clinical syndrome resulting from decreased renal function and azotaemia is called uraemia. a) Renal azotaemia results from renal disease, such as glomerulonephritis and chronic pyelonephritis. b) Pre-renal azotemia results from such conditions as severe dehydration, hemorrhagic shock, and excessive protein intake. c) Post-renal azotemia results from such conditions as ureteral or urethral stones or tumours and prostatic obstructions.  Clearance - a theoretical concept defined as the volume of plasma from which a measured amount of substance can be completely eliminated, or cleared, into the urine per unit time - can be used to estimate glomerular function. BLOOD UREA NITROGEN:  Urea, an end product of protein metabolism, is produced in the liver. From there, it travels through the blood and is excreted by the kidneys. Urea is filtered at the glomerulus, where the tubules reabsorb approximately 40%. Thus, under normal conditions, urea clearance is about 60% of the true GFR. CLINICAL LABORATORY TESTS USED IN THE EVALUATION OF DISEASE STATES, AND INTERPRETATION OF TEST RESULTS

PHARMD GURU Page 3 Where ClCR is the creatinine clearance in millilitres per minute, Cu is the concentration of creatinine in the urine, V is the volume of urine (in millilitres per minute of urine formed over the collection period), and CCR is the serum creatinine concentration.  Suppose the serum creatinine concentration is 1 mg/dL, and 1440 mL of urine was collected in 24hrs (1440mins) for a urine volume of 1 mL/min. The urine contains 100 mg/dL of creatinine. Creatinine clearance is calculated as:  Incomplete bladder emptying and other problems may interfere with obtaining an accurate timed urine specimen. Thus, estimations of creatinine clearance may be necessary. These estimations require only a serum creatinine value. One estimation uses the method of Cockcroft and Gault, which is based on body weight, age, and gender. a) This formula provides an estimated value, calculated for males as: b) For females, use 0.85 of the value calculated for males. EXAMPLE: A 20-year-old man weighing 72 kg has a CCR of 1.0 mg/dL; thus  Determination of GFR. The modified diet in renal disease (MDRD) equation is considered a more accurate measurement of GFR than other equations used to estimate renal function (e.g., Cockcroft –Gault) in patients with reduced GFR and is used in staging renal disease. Patients must have a serum creatinine concentration.