Measurement of renal function Flashcards
- Renal clearance - Measurement of creatinine clearance - Measurement of renal blood flow
Risk factors for kidney failure
The extremes of age: Very young and very elderly.
Polypharmacy
Specific disease: Hypertension Diabetes Chronic HF UTIs
Long term analgesia treatment
Transplant patient- rejection and anti-rejection drugs
Drug theraphy
Imaging procedures- radiocontrast can be nephrotic
Clinical signs and symptoms of fluid imbalance
Sign- oedema
Symptoms- breathlessness
Clinical signs and symptoms of electrolyte imbalance/ dysregulation
Signs:
Abnormal ECG- Absent P waves, broad QRS, Peaked T waves
Clinical signs and symptoms of EPO production dysfunction
Signs:
Pallor
Symptoms:
- Fatigue
Clinical signs and symptoms of Vitamin D3 dysfunction
Sign:
Osteomalacia- softening of bones
Symptoms:
Bone pain
Clinical signs and symptoms of Excretion dysfunction
Signs:
- Uremia
- Raided blood creatinine
Symptoms:
- Nausea/ vomitting
- Pruritus: severe itching of skin
Clinical signs and symptoms of acid-base imbalance
Signs:
- Low/high blood pH
- Low/high bicarbonate levels
Symptoms:
- Tachypnea
- Deep breathing
Bedside clinical data to assess patient’s clinical condition
Weight charts- rapid weigh gain/ loss
Fluid balance charts
Degree of oedema
Urine dipstick results
Imaging techniques for assessing renal function
Renography- macroscopic views of renal blood flow, filtration of excretory function
Gamma camera planar scintigraphy
PET scan
SPECT - single photon emission computerised tomography
Plasma creatinine
End product from the breakdown of creatine phosphate in the muscles
Filtered at the glomerulus
Secreted at the PT
Normal range of plasma creatinine
40-120 micro-mol/L
Factors that show increased plasma creatinine
Increased muscle mass
Dietary intake
Drugs that interfere with analysis- cephalosporins, dexamethasone
Drugs that inhibit tubular secretion
Ketoacidosis
Ethnicity- higher creatine kinase activity in black population
Factors that show decreased plasma creatinine
Low muscle mass
Cachexia/ starvation
Immobility
Pregnancy
Sever liver disease
Drugs that inhibit tubular secretion of creatinine
Cimetidine
Trimethoprim
Aspirin
Classifications of plasma creatinine concentrations as an indicator for renal function:
- Normal
- Mildy reduced
- Moderately reduced
- Severely reduced
- Very severely reduced
Normal: 120-150 [40-150]
Mildly reduced: 150-300
Moderately reduced: 300-500
Severely reduced: 500-700
Very severely reduced: >700
Plasma urea
Waste product of protein digestion- produced in the liver
Filtered in the glomerulus, secreted and reabsorbed in the tubule
Normal range of plasma urea
Range that indicates moderate- severe renal failure
Normal: 2.5-7.5 mmol/L
Renal failure: >20mmol/L
Factors that increase blood urea nitrogen
High protein diet
Hypercatobolic conditions: severe infection, burns, hyperthyroidism
GI bleeding
Muscle injury
Drugs: gluccorticoids, tetracycline
Hypovolaemia
Factors that decrease blood urea nitrogen
Malnutrition
Liver disease
Sickle cell- increased GFR
SIADH- syndrome of inappropriate ADH
Examples of renal clearance
- Filtered and not reabsorbed or secreted
- Filtered and some reabsorbed: electrolytes
- Filtered and completely reabsorbed: glucose, amino acids
- Filtered and primarily secreted into the tubule: PAH
Substance that is filtered and not reabsorbed or secreted
Inulin
The excretion rate is equal to the rate at which it is filtered
Inulin
Inulin is a plant polysaccharide filtered and not secreted/ reabsorbed.
Inulin filtration rate = GFR
Inulin is injected into the blood through an IV.
If a substance filtration rate > inulin clearance, then it is being secreted
Renal clearance
The volume of plasma completely cleared of a given substance in a unit time.
Clearance of X = Urine concentration of (X) x Volume of urine in a given time / Concentration of X in plasma
GFR
The rate at which filtrate is produced in the kidneys
- roughly 125mL/min (inulin filtration rate)
Used to measure renal function
Drawbacks of using inulin to measure GFR
Has to be given IV
Analysis of inulin in the blood and urine is technically demanding
Creatinine clearance
Creatinine is filtered and secreted in the PT
Creatinine clearance gives overestimation by 20%
- This is cancelled out by using colorimetry which underestimates by 20%.
Can be adjusted to take into account body surface area
Advantages of creatinine clearance over inulin clearance
Creatinine avoids IV infusion as it is endogenous.
Easy to analyse compared to inulin.
Formulas used to estimate GFR using creatinine clearance
Cockcroft-Gault
Modification of Diet in Renal disease [MDRD]- used more in the UK and takes into account ethinicity
GFR classifications for:
- Normal kidney function
- Mildy reduced
- Moderately reduced
- Severely reduced
- Very severely reduced
Normal- 90+ (stage 1 kidney disease)
Mildly reduced: 60-89 (stage 2)
Moderately reduced:
45-59 (3A)
30-44 (3B)
Severely reduced:
15-29 (4)
Very severely reduced:
<14 (stage 5)
PAH
Para-aminohippuric acid
- substance that is completely cleared from the plasma
- Its clearance rate= renal plasma flow
PAH clearance
90% of PAH is secreted into the PT.
10% left in the plasma in venous renal blood.
- Used to calculate effective renal plasma flow
- The 90% of PAH in urine is corrected to find total renal plasma flow by weighing it to 100%.
Total renal blood flow is calculated by adding haemocrit (extra 45%)
Biomarkers of renal disease
Urinary albumin/ protein secretion- indicator of chronic kidney disease
- Kidney injury molecule-1: KIM-1 in urine
- IL-18 in urine
- Fatty-acid binding proteins in urine
- Neutrophil gelatinase-associated lipocalin (in plasma and urine
- Cystatin C in plasma
