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Theme 3: The Excretory System and Renal Function > Measurement of renal function > Flashcards

Measurement of renal function Flashcards

1
Q

Why measure renal function

A

Identification of renal impairment in your patient

Modification of dosage of drugs which are cleared by the kidneys

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2
Q

Patients at risk of developing renal failure

A

Extremes of age: neonates and the elderly

Polypharmacy

Specific disease states: hypertension, chronic heart failure, diabetes, arthritis, renal disease, recurrent urinary tract infections

Patients receiving long term analgesics

Transplant patients

Drug therapy

Patients undergoing imaging procedures

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3
Q

Monitoring a patient’s renal function

A

Patients clinical condition

Modern imaging techniques

Biochemical data

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4
Q

Fluid balance affected

A

Clinical sign: oedema

Symptoms: breathlessness

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5
Q

Electrolyte refulation especially K+, Na+, PO42- and Ca2+ affected

A

Clinical signs: abnormal ECG, absent P waves, broad QRS complex, peaked T waves

No symptoms

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6
Q

EPO production affected

A

Clinical signs: pallor

Symptoms: fatigue

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7
Q

Vitamin D3 affected

A

Clinical signs: osteomalacia

Symptoms: bone pain

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8
Q

Excretion affected

A

Clinical signs: raised blood urea and creatinine concentrations

Symptoms: pruritis, nausea and vomiting

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9
Q

Acid base balance affected

A

Clinical signs: low blood pH and bicarbonate levels

Symptoms: deep and rapid respiration

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10
Q

Use of bedside clinical data

A

Weight charts

Fluid balance chart

Degree of oedema

Results of urine dipstick testing (urinalysis for protein, blood, glucose)

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11
Q

Modern imaging techniques

A

Macroscopic views of renal blood flow, filtration and excretory function

Some used clinically, some only currently used experimentally in the lab

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12
Q

Renography

A

Gamma camera planar scintigraphy

Positron emission tomography

Single photon emission computerised tomography

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13
Q

Biochemical data

A

Useful for identifying renal impairment

Blood markers of renal function

  • plasma or serum creatinine
  • plasma or serum urea or blood urea nitrogen
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14
Q

Creatinine

A

Breakdown product of creatine phosphate in muscle

Generally produced at a constant rate

Filtered at the glomerulus with some secretion into the proximal tubule

Normal range in plasma: 40-120umol/L

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15
Q

Plasma creatine increased by

A

Large muscle mass, dietary intake

Drugs which interfere with analysis

Drugs which inhibit tubular secretion

Ketoacidosis

Ethnicity (higher creatine kinase in black population)

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16
Q

Plasma creatinine decreased by

A

Reduced muscle mass

Cachexia/ starvation

Immobility

Pregnancy (increased plasma volume in mother)

Severe in liver disease

17
Q

Plasma creatinine as an indicator of renal function

A

Normal adult adult range: 100 (40-120)

Normal kidney function: 120- 150

Mildly reduced kidney function: 150-300

Moderately reduced kidney function: 300-500

Severely reduced kidney function: 500-700

Very severely reduced kidney function: >700

18
Q

Urea

A

Liver produces urea in urea cycle as waste product of protein digestion

Filtered at the glomerulus, secreted and reabsorbed in the tubule

Plasma urea BUN

Normal range: 2.5-7.5mmol/L

19
Q

Blood urea nitrogen increased by

A

High protein diet

Hypercatabolic conditions

Gastrointestinal bleeding

Muscle injury

Drugs

Hypovolaemia

20
Q

Blood urea nitrogen decreased by

A

Malnutrition

Liver disease

Sickle cell anaemia

SIADH

21
Q

Examples of renal clearance

A

Filtered by the glomerulus and not reabsorbed e.g. inulin

Filtered and some of the filtered portion is reabsorbed e.g. Na+

Filtered and completely reabsorbed e.g. glucose and amino acids

Primarily secreted into the tubule e.g. PAH

22
Q

Clearance

A

The volume of plasma completely cleared of a given substance in unit time

Provides information about functions of the kidney

  • glomerular filtration
  • tubular reabsorption
  • tubular secretion
23
Q

Renal clearance drawbacks

A

Measuring clearance means measurement of overall nephron function- 2 million nephrons in both kidneys

Gives sum of all transport processes occurring

No information about precise tubular sites of mechanisms of transport

24
Q

Glomerular filtration rate

A

Rate at which filtrate is produced in the kidneys

Can be measured clinically and used as an indicator of renal function

Can be estimated by measurement of clearance of cretinine

More accurate estimation is measurement of inulin clearance as it is not secreted into tubule

25
Q

Inulin clearance for measurement of GFR

A

Plant polysaccharide

Freely filtered but not secreted and not reabsorbed

Rate of excretion in urine equals rate of filtration by the kidneys

26
Q

Drawbacks of inulin clearance to measure GFR

A

Not clinically useful

  • must be administered by IV to get relatively constant plasma or serum levels
  • chemical analysis of inulin in serum and urine is technically demanding
  • could use radiolabelled compounds instead
  • may also bind to proteins and distort results
  • problems of IV infusion of GFR markers are avoided by using an endogenous substance with inulin like properties e.g. creatinine
27
Q

Creatinine clearance

A

Filtered at the glomerulus but some also secreted into the proximal tubule

Using the equation would over estimate GFR by about 20% in humans

Colorimetry methods used to measure creatinine under estimates creatinine concentrations by about 20%

2 errors cancel each other out

28
Q

Adjustments due to body surface area

A

Creatinine clearance can also be adjusted to take account of body surface area

Corrected creatinine clearance= meausre CrCl x1.71/BSA

29
Q

Estimation of GFR using serum creatinine only

A

Allows estimation of GFR without having to collect urine samples

Cockcroft- Gault Formula

Modification of diet in renal disease formula

30
Q

Using PAH clearance to measure renal blood flow

A

If a substance is completely cleared from the plasma its clearance rate will be equal to renal plasma flow

Clearance of PAH can be used to estimate this

Not normally present in blood

Theme 3: The Excretory System and Renal Function (13 decks)

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