TESTS OF RENAL FUNCTION AND HYDRATION STATUS

Question 1

Define and outline pre-renal, renal and post-renal kidney failure

Answer 1

Pre-renal e.g. decreased ECFV or MI
Renal e.g. acute tubular necrosis
Postrenal e.g. ureteral obstruction

Question 2

Define and outline anuria, oliguria and polyuria

Answer 2

Oliguria: Production of little urine. GFR reduced. ADH increased. Concentrated urine / low volume. Renal hypo perfusion causes to renin, secretion. Functioning nephrons increase sodium reabsorption (aldosterone). Urine sodium concentration is low
Anuria: failure of the kidneys to produce urine
Polyuria: production of abnormally large volumes of dilute urine.

Question 3

UREA:

Answer 3

quick, simple measurement. wide reference range 3 - 8 mmol/L. sensitive but non-specific index of illness
It’s filtered at the glomerulus, 40% is reabsorbed by renal tubules in health. More is reabsorbed if the rate of tubular flow is slow e.g. hypo perfusion. Useful test but must be interpreted with great care. Always consider input, output and patient’s fluid volume.

Question 4

PLASMA CREATININE

Answer 4

50 - 140 umol/L, increases in concentration as GFR decreases. analytical interferences
(acetoacetate - DKA) NOT proportional to renal damage. Change within an individual patient is usually more important than the absolute value. Plasma creatinine in chronic renal disease may increase to 1000 umol/L
Plot of reciprocal of plasma creatinine concentration predicts when intervention is required in end stage renal failure.

Question 5

SODIUM

Answer 5

Normal blood sodium levels are 135 - 145 mmol/litre. Often too much Na in body during kidney disease, but sometimes doesn’t show up due to dilution due to patients drinking too much water as too much Na makes you thirsty. The risk of both hypo- and hypernatremia can increase with advancing stages of CKD.

Question 6

Understand the basic equation use for measure creatinine clearance

Answer 6

Ccreat = Ucreat x V [RR 100 - 130 mL/min] DIVIDED BY Pcreat

Question 7

Creatinine clearance

Answer 7

in health 10-30% higher than GFR. Tubular secretion increased in chronic renal disease
Tubular secretion inhibited by drugs, e.g. salicylate, cimetidine. Problems with incomplete collection so = unreliable test.

Question 8

eGFR values seen in patients during the various stages of kidney failure

Answer 8

Stage 1 = GFR 80+ which means observation and control of blood pressure needed. Shows normal kidney function. Stage 5 = GFR <15 or on dialysis. May need transplant