the role of clinical biochemistry in renal disease Flashcards
what key analyses are available in the lab? 9
- U&E request gives serum concentrations of:
- Creatinine- reference interval is higher in males than females
- Urea
- Sodium
- Potassium
- E-GFR calculated using serum creatinine concentration
- .
- Urine:
- Albumin: creatinine ratio (ACR)
- Protein: creatinine ratio (PCR)
- .
- Plus, a range of supporting assays for AKI or CKD
describe kidney blood flow?
1500 mL/min
describe the measurement of glomerular filtration?
what does it require? 2
- GFR= (U x V)/S= ml/min
- U= urine concentration
- V= urine flow rate
- S= serum concentration
- A substance that is filtered and then neither absorbed or secreted in the renal tubules
- 24h urine collection and a blood sample
why do we use creatinine for GFR? 5
- Derived from creatine in muscle
- Serum concentrations are relatively stable
- 24h urine output is also stable day to day
- No absorption and very little secretion in renal tubules
- Simple to measure
what causes variation in serum concentrations and 24 hour urine output? 5
- Age
- Sex- male> female
- Lean body mass
- Ethnic origin
- Effect of diet
how do we overcome the variations in serum concentrations and 24 hour urine output? 5
- GFR related to body surface area- so standardise to a given body surface area
- This allows:
- Comparison against the general standard
- Staging of renal disease
- Monitoring of change in renal function- individual or cohort
- Chosen standard= 1.73m^2
what does very high plasma glucose cause?
an osmotic diuresis leading to loss of water and sodium
describe dehydration? 3
- Very likely is the serum urea: creatinine ratio is greater than 100
- The mechanism is the passive re-absorption of urea in the nephron at low flow rates
- Serum protein concentrations may also be elevated
how can we tell someone has AKI? 4
- A rise in serum creatinine of 26 or greater within 48 hours
- A 50% of greater rise in serum creatinine known or presumed to have occurred within the last 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 and young people
- A 25% or greater fall in eGFR in children and young people
describe the AKI alert system? 3
- Stage 1= rise of. >1.5x baseline level
- Stage 2= rise of >2x baseline
- Stage 3= rise of 3x baseline
what are the causes of AKI? 5
P- poor perfusion (loss of isotonic fluids)
S- sepsis (any severe infection)
T- toxins (drugs)
O- obstruction (renal calculus, prostatic enlargement)
P- parenchymal (glomerulonephritis)
describe body builders and liver function? 5
- High serum creatinine
- High serum creatine kinase
- High urea albumin: creatinine ratio
- This is because they have a high muscle mass and protein intake
- Mild hypokalaemia is not uncommon in body builders
what is the origin of creatinine? 2
- Muscle mass is proportional to creatine and creatinine
Creatine + ATP= creatinine
describe some causes of CKD? 9
- Hypertension
- Diabetes
- Hyperlipidaemia
- Recurrent renal infection
- Chronic glomerulonephritis
- Systemic disease (systemic lupus, multiple myeloma)
- Genetic- polycystic kidney, Alport syndrome
- Chronic obstruction prostatic hypertrophy, renal calculi, reflux
- Medication- NSAIDS, lithium
describe the albumin: creatinine ratio? 4
- Proteinuria is a 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 filtered but metabolised in the proximal tubule. At larger loads due to glomerular damage more albumin escapes into the urine
- Measurement as a ration with creatinine allows the use of a random urine sample rather than a timed collection
describe the different stages of CKD and the different eGFR? 6
1- normal- >90 2- mild reduction- 60-89 3a- mild-moderate reduction- 44-59 3b- moderate-severe reduction- 30-44 4-severe reduction- 15-29 5- kidney function <15
describe the metabolic features of CKD? 4
2- elevated serum urea and creatinine concentrations, some increase in the serum parathyroid hormone concentration
3- calcium absorption decreased, lipoprotein lipase decreased, malnutrition, anaemia- erythropoietin decreased
4- elevated serum triglyceride concentration, elevated serum phosphate concentration, metabolic acidosis, hyperkalaemia
5- marked elevation of serum creatinine and urea concentrations
what is the importance of lab results for the treatment of CKD? 9
- Elevated urea- low protein diet
- High potassium- diet, diuretics, treat acidosis
- Low bicarbonate- bicarbonate supplements
- Low haemoglobin- iron supplements and possible erythropoietin with a target Hb 100-120
- Low ferritin and transferrin saturation- iron supplements with a target saturation of >20%
- Low calcium- reduce serum phosphate, vitamin D supplements
- Raised phosphate- phosphate binding drugs
- Raised PTH- raise serum calcium, calcimimetric drugs to keep PTH within 2-9 x upper limit of RI
- Raised TG- diet, weight reduction, statins
what is the role of the lab in finding the cause of renal disease? 7
- AKI:
- Plasma lactate- prognostic indicator
- Infection- serum procalcitonin, CRP, WBC, blood culture
- Autoimmune causes
- .
- CKD:
serum and urine light chains- myeloma - Glycated Hb- diabetic control
- Antibody tests
- Biopsy- histology
how do we monitor renal dialysis? 9
- Pre and post dialysis samples
- Show the effectiveness of dialysis
- Indicate the required frequency of dialysis
- Determine the need for other interventions
- Diet
- Supplements
- Phosphate binders
- Lipid lowering agents
- Iron supplements
how do we monitor renal transplant patients? 6
- Serum creatinine- transplant function
- E-GFR
- ACR or OCR- potential damage to transplanted kidney
- Measuring anti-rejection drugs
- Checking for any tubular dysfunction
- Monitoring as for CKD 3
when is an individuals GFR required? 2
- Remember MDRD and CKD- epi are linked to a standard body surface area
- The real GFR of an individual is required to determine the dose of renally excreted drugs that are potentially toxic, monitoring dialysis and transplant patients
describe the Cockcroft and Gault measurement of GFR? 2
- GFR= (140-age) x (weight x constant)/ serum creatinine
- Constant= 1.23 in males and 1.04 in females
describe renal tubular disorders? 4
- There are many and they may be inherited or acquired
- Renal tubular acidosis
- Fanconi syndrome
- Diabetes insipidus
what are the next tests? 3
- Early morning urine pH- this will be greater than 5.5 in type 1 renal tubular acidosis with hypokalaemia
- Treatment to reduce the risk of nephrocalcinosis/ renal stone formation:
- Potassium citrate, sodium bicarbonate, thiazide diuretics
