Assessment of Renal Function Flashcards
What are the main functions of the kidney?
- Homeostasis: water, salt, acid-base status
- Excretion of waste products: non-proteinous nitrogen compounds; urea , creatinine, uric acid, and excess inorganic substances; sodium, Cl, Ca, K, Mg, sulfate, and excess water.
- Hormone production: erythropoietin, renin, prostaglandins, 1a-vitD3 hydroxylation.
What are symptoms of Kidney Disease?
- Often none
- Symptoms/signs of hypertension such as swollen ankles, high blood pressure, headaches, visual disturbances
- Changes in urinary frequency or volume
- In stages 4 and 5 of CKD: fatigue, nausea, vomiting, poor appetite, shortness of breath, fluid retention.
Reduction of 50-60% functional renal mass may occur before any signs or biochemical abnormalities manifest. Regular monitoring of those at risk therefore very important; CVD, HT, DM, genetically at risk individuals
What are some laboratory investigations for Kidney Disease?
- Imaging: Ultrasounds, CT/MRI
- Histology and microscopy (although renal biopsy rarely used)
- Immunology
- Biochemistry: Urinalysis and Quantitative biochemical markers
What are the advantages and disadvantages of imaging?
Advantages
- Size/ symmetry/ obstruction to urine flow anywhere
- Imaging of kidney, bladder, ureters, prostate gland
Disadvantages
- Expensive
- Difficult to assess extent of functional damage.
What is seen on histology of the kidney?
Acellular
- Hyaline
- Granular
- Waxy
- Fatty
- Pigment
- Crystal
Cellular
- RBC
- WBC
- Bacterial
- Epithelial
Which immunological tests are done in the kidney?
- Complement: low C4 seen in Systemic Lupus Erythematosus (SLE) & cryoglobulinaemia.
- Anti-glomerular basement membrane antibodies: associated with Goodpasture’s disease (kidney & lung disease).
- cANCA: associated with vasculitis esp. Wegener’s disease.
- pANCA: associated with vasculitis.
What are disadvantages of immunological testing and histology/microscopy?
Immunological: Only useful in specific diseases
Histology/Microscopy: Biopsy invasive, only a ‘snapshot’.
What is Anuria, Polyuria, and Oliguria?
- Anuria: <100mL/24h
- Oliguria: <400mL/24h
- Polyuria: >3L/24h OR >50mL/kg mass/24h
What are some limitations for Urinalysis?
- Potential for operator error.
- Inter-operator variability, even with automation.
- Requires fresh urine, in date, properly stored dipsticks
- Poor sensitivity and specificity - sensitivity depends on concentration of urine
What are some interferences for Urinalysis?
- Blood analysis: menstruation (+ve), vit. C (-ve)
- Protein analysis: infected urine (+ve), dilute urine (-ve)
What are Quantitative biochemical measurements?
Glomerular filtration/function
- Urea
- Creatinine
- Proteinuria
Tubular function
- Urine volume/osmolality
- pH
- Phosphate
- Aminoaciduria
- Glycosuria
- β2-microglobulin
What is the biochemical measurement used for Fanconi Syndrome?
Assessment of Tubular function using
- Phosphate
- Aminoaciduria
- Glycosuria
What are ideal markers of kidney function?
- Freely filtered
- Not reabsorbed
- Not secreted
- Not metabolized
- Not synthesized in the renal tubules/ kidney
What are some exogenous markers of kidney function?
- Inulin (‘gold standard’)
- 125I-Iothalamate
- 51Cr-EDTA
- 99mDTPA
- Iohexol
What are advantages and disadvantages of Inulin?
Inulin (‘gold standard’)
Advantages
- Metabolically inert sugar
- Provides good GFR estimation
Disadvantages
- Non-endogenous (intravenous administration)
- Assay not widely available
- Expensive