Assessing Renal Function

Front 1

Normal Kidney
- EM

Back 1

Front 2

EPO

Back 2

Front 3

Vit D

Back 3

Front 4

Failing Kidneys

Back 4

1. Toxins build up:
–Urea (nausea)
–Potassium (weakness and heart rhythm)
–Phosphate (itch, PTH and bone disease)
–Acid (breathlessness and bone disease)
2. Water retention:
–Fluid in the lungs (breathlessness)
–Fluid in the legs (oedema)
–High blood pressure +/- hormone effect
3. Erythropoietin deficiency:
– Anaemia (tiredness, lack of energy, breathless)
4. Vitamin D deficiency:
–Low calcium (pins and needles, cramps)
–Bone disease (PTH, bone pain, factures)

Front 5

Simple assessment of kidney function

Back 5

•Abnormal kidney function: Blood tests
–Increased urea
–Increased creatinine
–Increased potassium
–Increased phosphate
–Increased acid (low bicarbonate level, low pH)
–Increased parathyroid hormone
–Increased renin
–Decreased haemoglobin (decreased erythropoietin)
–Decreased calcium
–Decreased vitamin D

•Abnormal kidney function: Examination
–Appearance: Pale (anaemic), sallow (uraemic)
–Smell: uraemic fetor
–Kussmaul’s respiration (metabolic acidosis)
–Abnormal movement: asterixis
–Hypertension
–Fluid retention (peripheral/pulmonary oedema)

Front 6

Reviewing patients with specific abnormalities:
FORMAL KIDNEY PROBLEMS

Back 6

–Reduced GFR (abnormal creatinine)
–Proteinuria
–Haematuria/pyuria/cast excretion
–Hyperkalaemia/acid-base disturbance
–Nocturia/frequency

Front 7

Purpose of renal function testing

Back 7

1. review patients with specific kidney abnormalities
2. Monitor patients on nephrotoxic Tx
–Lithium
–Cyclosporin
–Chemotherapy
3. Determine normal renal fn
- kidney donor work up
–Post partum following pre-eclampsia
–Post nephrectomy

Front 8

Renal clearance

Back 8

•Is the measure of the ability of a kidney to clear a given substance
•Renal clearance is effected by:
–Glomerular filtration
–Tubular secretion
–Tubular reabsorption
–Metabolism
•Main use is to determine glomerular filtration rate: our best estimate of “renal function”

Front 9

Measurement of renal clearance

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Front 10

Inulin

Back 10

–Freely filtered by the glomerulus
–No tubular secretion or reabsorption
–Best measure of GFR: impractical

Front 11

Creatinine

Back 11

–Freely filtered by the glomerulus
–Some tubular secretion
–Can overestimate the inulin GFR (10-20%)
–Can be improved by using cimetidine

Front 12

Urea

Back 12

–Freely filtered by the glomerulus
–Some tubular reabsorption
–Underestimates the inulin GFR

•Average of urea and creatinine clearance:
–Can help adjust for the tubular effects

Front 13

•Paraaminohippurate (PAH):

Back 13

–Freely filtered
–Active tubular secretion
–Complete removal of the PAH from the plasma in a single pass of the kidney
–Therefore is used as a measure of Renal Plasma Flow
–Little clinical utility

Front 14

BSA

Back 14

•Using Body Surface Area (BSA)
–e.g. DuBois and DuBois equation
•Clearance = ml/min/1.73m2
•BSA of 1.73m2 considered to be average

Front 15

Estimates of GFR

Back 15

•Nuclear GFR

Front 16

MDRD limitations
- eGFR

Back 16

only accurate in impaired renal function patients (because thats where oit was extrapolated from)
- so if normal its given in >60ml?min

Front 17

Nuclear GFR

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Front 18

Relationship between GFR and Cr

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so not till below 50% is it not normal any more

NON-LINEAR

Front 19

Ageing and the Kidney

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Front 20

Urinary concentrating ability
tests

Back 20

•Tested using:
–Overnight water deprivation (from 10pm)
–Maximised using synthetic ADH (intra-nasal)

measure morning urine volume
- give the ADH and test urine osmolality

THIS PATIENT: impaired ability to concentrate (thus its not ADH dependednt but kidney problem)

Front 21

What is this called?

Back 21

Nephrogenic diabetes Insipidus

Front 22

Acidification ability
Bicarbonate

Back 22

•Bicarbonate:
–Is freely filtered by the glomerulus
–The MAJORITY is reabsorbed by the proximal convoluted tubules
–Some is also reabsorbed by the distal tubules

Front 23

–Tubular disease can lead to excessive losses of bicarbonate and result in a systemic acidosis

Q: What name is given to this abnormality?

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A: Proximal renal tubular acidosis

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Acid Excretion

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•Acid:
–Is actively excreted into the urine in the distal tubule

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–Tubular disease can lead to excessive accumulation and result in a systemic acidosis

Q: What name is given to this abnormality?

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A: Distal renal tubular acidosis

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•How to test for an acidification defect?

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•Blood test:
– Acidosis (pH < 7.35)
– Anion gap = Na - Cl - HCO3, (Normal 8-16)
– Renal tubular disease: normal anion gap acidosis
• Urine test:
– Urinary pH
– Urinary bicarbonate
– Formal acidification study

Front 27

• Acidification test using oral ammonium chloride

Back 27

- ammonium chloride a weak acid

shouldve been 5.2 (thus the defect in acid excretion in the distal - i.e incomplete distal renla tubular acidosis)