blood tests to assess renal function Flashcards
what is the equation for GFR and what do the individual elements mean?
GFR = (U x V)/S = ml/min
U = urine concentration mmol/L V = urine flow rate ml/min S = serum concentration mmol/L
what are the 2 requirements to measure glomerular filtration?
1) a substance that is filtered and then neither absorbed or secreted in the renal tubules
- 24h urine collection and blood sample
where is creatinine derived from?
creatine in muscle
what gives variation in serum concentration and 24h urine output?
- age
- gender: male > female
- lean body mass: ethnic origin
- effect of diet
how is dehydration assessed?
- dehydration is very likely if the serum urea:creatinine ratio is greater than 100
- some people use 80 as the cut off
- the mechanisms if the passive re-absorption of urea in the nephron especially at low flow rates
- serum protein concentrations also might be elevated
what are the criteria to detect acute kidney injury (AKI)?
- a rise in serum creatinine of 26 or greater within 24 hours
- a 50% or greater rise in serum creatinine known or presumed to have occurred within the past 7 days
- a fall in urine output to less than 0.5ml/kg/hr for more than 6 hours for adults and more than 8 hours in children or young people
- a 25% or greater fall in eGFR in children and young people < 18 years old
what are the causes of AKI?
- P = poor perfusion: loss of isotonic fluids
- S = sepsis: any severe infection
- T = toxins: drugs
- O = obstruction: renal calculus, prostatic enlargement
- P = parenchymal: glomerulonephritis
what are the causes of CKD?
- hypertension
- diabetes: type 2 mellitus > type 1 mellitus
- hyperlipidaemia
- recurrent renal infecitons
- chronic glomerulonephritis: IgA nephritis
- systemic disease: systemic lupus, multiple myeloma
- genetic: polycystic kidney, Alport syndrome
- chronic obstruction: prostatic hypertrophy, renal calculi, reflux
- medication: NSAIDs, lithium
what is the importance of the albumin:creatinine ratio?
- proteinuria is common finding in renal disease
- normally large proteins are retained by the glomerulus and only small proteins such as amylase are filtered
- a small amount of albumin is normally filleted but metabolised in the proximal tubule
- larger loads due to glomerular damage means more albumin escapes into the urine
- measuring as a ratio with creatinine allows use of a random urine sample rather than a time collection
what are the metabolic features of stage 2 CKD?
- elevated serum urea and creatinine concentrations
- some increase in serum parathyroid hormone (PTH) concentration
what are the metabolic features of stage 3 CKD?
- calcium absorption decreases
- lipoprotein lipase decreased
- malnutrition
- anaemia
what are the metabolic features of stage 4 CKD?
- elevated serum triglyceride concentration
- elevated serum phosphate concentration
- metabolic acidosis
- hyperkalaemia
what are the metabolic features of stage 5 CKD?
- marked elevation of serum creatinine and urea concentrations
what is the intervention for elevated urea?
low protein diet
what is the intervention for high potassium?
- diet
- diuretics
- treat acidosis
what is the intervention for low bicarbonate?
bicarbonate supplements
what is the intervention for low haemoglobin?
iron supplements and possible erythropoietin with a target Hb of 100-120g/L
what is the intervention for low ferritin and transferrin?
iron supplements with a targeted satn > 20% and ferritin 100-600
what is the intervention for low calcium?
- reduce serum phosphate
- vitamin D supplements: often 1-alpha OH via D3
what is the intervention for raised phosphate?
phosphate binding drugs
what is the intervention for raised PTH?
- raised serum calcium
- calcimimetic drugs to keep PTH within 2-9 x upper limit of RI
what is the intervention for raised triglyceride?
- diet
- weight reduction
- fibrate or statin drugs
what is looked for in the lab with AKI?
- plasma lactate
- infection
- autoimmune causes
what is looked for in the lab with CKD?
- serum and urine light chains
- glaciated Hb
- antibody tests
- biopsy
