Renal Flashcards
3 equations for eGFR
- Cockcroft-Gault equation (tend to overestimate patients)
- MDRD equation (tend to underestimate normal subjects)
- CKD-EPI (recommended)
Reference interval of GFR
90~120 ml/min/1.73m^2
Cockcroft-Gault equation
(140 - age) ⨉ weight / (P_Cr ⨉ 72) , times 0.85 for female
Parameters in CKD-EPI
Cr, age, gender, race
Reference interval of creatinine
70~150 µmol/L
creatinine clearance equation
Clearance ⨉ P_Cr = U_Cr ⨉ V_U
(ml/min)
Limitation of creatinine
FP: drugs
FN: lower muscle mass
FP & FN of urea (4+4)
FP: high protein diet, catabolic state, GI bleed, dehydration
FN: low protein diet, fasting, liver disease, over-hydration
Urea:Creatinine ratio range indicating pre-renal failure
> 80:1
Oliguric definition
urine output <400 ml/day
OR <0.5 ml/kg/hr
Anuric definition
urine output <50 ml/day
Acute kidney injury definition in KDIGO definition
(any one of the following)
a. Urine output <0.5 ml/kg/h for 6h
b. Serum Cr ↑ 1.5x baseline in 7d
c. Serum Cr ↑ >26.5 µmol/L in 48h
Clinical staging of acute kidney injury
Stage 1: serum Cr ↑ 1.5~2x, oliguric for 6h
Stage 2: serum Cr ↑ 2~3x, oliguric for 12h
Stage 3: serum Cr ↑ >3x, anuric for 12h
Causes of pre-renal failure
↓ ECV: dehydration, GI bleed, third spacing…
↓ cardiac output: CHF, MI…
Shock
Renal vascular disease: RAS, MAHA
Drugs: NSAID, ACEI
Which region is most vulnerable in acute tubular necrosis?
proximal convoluted tubule
Causes of acute tubular necrosis
ischaemia / toxins
Nephrotoxins that cause acute tubular necrosis (8)
Iatrogenic: aminoglycosides, amphotericin B, cisplatin, contrast
Metabolic: haemoglobin, myoglobin, urate
heavy metal
Natural history of acute tubular necrosis
oliguric phase –> anuric phase –> recovery phase, each lasts for one week
How to differentiate pre-renal injury and acute tubular necrosis with urine electrolyte?
FENa: (<1%; >2%)
Urine Na: (<20; >40)
Urine:plasma Cr ratio: (>40; <20)
Urine osmolality: (>500; <350)
Plasma UCR: (>80;<80)
Equation for fraction of Na excretion
(U_Na/P_Na) ➗ (U_Cr/P_Cr) ⨉ 100%
Definition of chronic kidney disease
progressive irreversible impairment of renal function >3m, as evidenced by
a. eGFR <60 ml/min/1.73m^2
b. albuminuria
i. albumin excretion rate >30 mg/day, or
ii. urine albumin: creatinine ratio >3 mg/mmol
Aetiology of chronic kidney disease (4)
- DM nephropathy (30%)
- Hypertension (25%)
- Glomerulonephritis (15%)
- Polycystic kidney disease (5%)
…
What is secreted in adaptation in chronic kidney disease to ↑ phosphate secretion?
FGF23 (fibroblast growth factor 23)
Pathogenesis for impaired concentrating ability in chronic kidney disease (3)
- ↓ medullary hypertonicity
- medullary fibrosis
- collecting duct resistance to ADH
Renal osteodystrophy (3)
Osteomalacia
Osteitis fibrosa cystica
Osteosclerosis
Renal replacement therapy indications
- eGFR <5 ml/min; or <10ml/min with ESRF s/s
- ## uraemic encephalopathy
- declining nutritional status
- persistent volume overload
- refractory acidosis / hyperkalaemia / hyperphosphataemia
Advantages of haemodialysis compared with peritoneal dialysis
- more efficient in small molecules
- much shorter period of dialysis
- lower dextrose & osmolality required
Proteinuria definition
> 0.15 g/day
(Nephrotic range: >3.5g/day)
Microalbuminruia deinition
30~300mg /day or ACR 3~30mg/mmol
Macroalbuminuria definition
> 300 mg/day
Pathological proteinuria exclusion criteria (4)
UTI, fever, heavy exercise in 24h, menstruation
Aetiology of proteinuria
- Orthostatic proteinuria
- Transient proteinuria
- Overflow proteinuria
- Glomerular proteinuria
- Tubular proteinuria
Size of protein that are not filtered through glomerular ultrafiltration
> 40kDa
MC isolated proteinuria in teenagers
Orthostatic proteinuria
MC proteinuria cause
Glomerular proteinuria
Limitations of urine dipstick for detecting proteinuria
- only detect >300mg protein
- only detect albumin
(do two times)
Compare severity of acidaemia of 3 types of RTA
type 1 > type 2 > type 4
Which type of RTA gives hypercalciuria, nephrolithiasis, and osteomalacia? What is the pathogenesis?
type 1
Severe acidaemia —> buffering of H+ from bones
Which type of RTA gives hypoK and hyperK?
hypoK: type 1, 2
hyperK: type 4
Which type of RTA gives -ve UAG?
type 2
Pathogenesis of type 1 RTA (relation to K)
impaired distal tubule to secrete H+
⨉ secrete H+ –> K+ is secreted in compensation
Management of type 1 RTA
Oral NaHCO3
Pathogenesis of type 2 RTA (relation to K)
↓ proximal HCO3- reabsorption
↑ HCO3 loss –> ↑ Na loss –> ↑ aldosterone & distal flow –> ↑ K secretion
Which RTA is associated to Fanconi syndrome?
type 2
Diagnosis of type 2 RTA
HCO3- loading test
FE of >15% HCO3
Management of type 2 RTA
IV NaHCO3 + K supplements
Pathogenesis of type 4 RTA
mieralocorticoid deficiency / resistance
Which 2 ions have serum concentrations normal until GFR <50% of normal in CKD patient?
H, phosphate
Effect of CKD on Ca metabolism
↓ phosphate excretion –> ↑ phosphate concentration –> hypocalcaemia –> secondary hyperPTH –> tertiary hyperPTH
↓ 1α-hydroxylation –> vitamin D resistance
