Clinical significance of BUN & creatinine BM 黃雅筠

Definition  Nitrogenous end products of metabolism  Dietary protein/tissue protein  urea (liver)  Affected by diet, hydration status  Muscle creatine  creatinine  Affected by muscle mass  Both excreted by kidneys  Small molecule uremic toxins  Urea (60Da), creatinine (113Da)  A test of renal function

Normal ranges  BUN  7~18 mg/dl (32.0 mg/dl)  Creatinine  male: 0.6~1.3 mg/dl (2.2 mg/dl  low GFR!)  female: 0.5~1.1 mg/dl  BUN/Cr  10~15: 1

BUN & Cr  BUN↑ = azotemia  ↑ protein intake  GI bleeding  Infection  Steroid, tetracycline  BUN ↓  ↓ effective circulatory blood volume  Pregnancy  Diuretic use  liver failure  Creatinine ↑  Malignant hypertension  Atheroembolic renal disease  GFR ↓  ↑ meat consumption  Creatinine ↓  Older age  Chronic myopathies  Pregnancy

BUN/Creatinine ratio  Chronic kidney disease: elevated BUN/Cr  Acute kidney injury  Prerenal azotemia: >20  Increased protein intake, dehydration  Intrinsic AKI: <10  Decreased protein intake, dialysis patients, protein atrophy

BUN/Creatinine ratio  Postrenal AKI (BUN/Cr = 32/2.2=14.5)

Clinical significance  Surrogate test for GFR  BUN and Cr  Advantages: fast, cheap  Disadvantages: low sensitivity  Creatine clearance (Ccr) (>100 ml/min)

Reference  NCBI  Clinical Methods: The History, Physical, and Laboratory Examinations. 3rd edition. Chapter 193 BUN and Creatinine.   義大醫院臨床病理科  Renal function test  nction.pdf nction.pdf  實驗診斷學－如何接觸腎臟病病人 郭弘典老師  急性腎損傷 郭美娟老師