Renal Flashcards
Anion gap calculation
Normal anion gap = 8-16 (Na + K ) - (Cl + HCO3)
Absorption in the proximal tubule
- Active Na reabsorption (60%) - Bicarb reabsorption (85-90%) - Secondary reabsorption of; Glucose Phosphate Amino acids LMW proteins Chloride
What is TYPE II renal tubular acidosis?
Proximal tubular acidosis Primary defect = impairment of HCO3- reabsorption in the proximal tubule
What is Fanconi’s syndrome?
Global proximal tubular dysfunction
Key features of Renal Fanconi syndrome
- LMW proteinuria - Glycosuria - Hypophosphataemia - Aminoaciduria - Hypouricaemia - Bicarb loss
Aetiology of Fanconi syndrome
Inherited - AR (mutation in gene encoding Na/HCO3 co transporter); short stature, blindness, enamel defects of teeth, ID - Cystinosis (AR mutation in CTNS gene) - Dent disease (X-linked recessive) OCRL 1 defect of CLC5 defect - Lowe syndrome (X-linked recessive), OCRL1 gene defect; congenital cataracts, mental retardation, Fanconi - Mitochondrial myopathies Metabolic disorders - Tyrosinemia type 1 - Galactosemia - Wilson’s disease - Hereditary fructose intolerance Heavy metal toxicity Drugs - Gentamicin - Cisplatin - Sodium valproate - Ifosfamide
LOWE syndrome triad
Congenital cataracts Mental retardation Fanconi syndrome
Distinguishing features between Dent disease + Lowe syndrome
Dent disease is distinguished clinically from the Lowe (oculocerebrorenal) syndrome by the absence of cataracts, mental developmental delay, and renal tubular acidosis.
Dent disease clinical features
LMW proteinuria Hypercalciuria (due to increased GIT Ca absorption) Nephrocalcinosis Kidney stones Kidney failure Rickets Polyuria Microscopic haematuria
Treatment of RTA type II
Sodium bicarbonate Potassium citrate (citrate also increases HCO3 levels) Oral phosphate Vitamin D
RTA type 1
Distal tubular dysfunction Impaired secretion of H+ in distal nephron Inability to excrete daily acid load - Progressive loss of buffer - Serum HCO3- <10 - Urine pH > 5.5 - Hypokalaemia with Na wasting - Hypercalciuria with risk of stones + nephrocalcinosis POSITIVE urine anion gap (Na + K) - (Cl)
Urine pH + RTA type 1
IF you have high levels of SERUM bicarb (e.g. on replacement) then the urine pH will HIGH IF you have LOW levels of SERUM bicarb the urine pH will be LOW as you will be in a metabolic acidosis and the distal tubules still work so will be actively pumping out H+ ions to try and improve the metabolic acidosis
RTA type I and II can cause a _____ anion gap metabolic ______
RTA type I and II can cause a NORMAL anion gap metabolic ACIDOSIS
RTA type I causes
PRIMARY - AD + AR mutations - Defects in Cl/HCO3 exchanged, carbonic anhydrase or H+ATPase - AR associated with SNHL SECONDARY - Autoimmune disorders - Nephrocalcinosis - Drugs: ifosfamide, amphotericin, lithium, ibuoprofen - Hypercalciuric conditions (hyperPTH, vit D intoxication) - EDS, Wilson, Marfan’s
What is cystinosis?
Systemic disease caused by a defect in the metabolism of cysteine that results in accumulation of cysteine crystals in the major organs of the body
Genetics of cystinosis
AR mutation in CTN5 gene
Clinical manifestations of cystinosis
i. Polyuria and polydipsia ii. Growth failure iii. Rickets iv. Fever – caused by dehydration or diminished sweat production v. Patients typically fair skinned and blond due to diminished pigmentation vi. Ocular presentations – photophobia, retinopathy, impaired visual acuity vii. Other – hypothyroidism, hepatosplenomegaly, delayed sexual maturation viii. With progressive tubulointerstitial fibrosis → renal fibrosis
Diagnosis of cystinosis
- Cystine crystals in the cornea
- White cell cysteine:
- Leukocyte cysteine content = elevated; confirms diagnosis
Treatment of cystinosis
i. Aimed at correcting metabolic abnormalities associated with Faconi syndrome or chronic renal failure ii. Cysteamine – which binds to cystine and converts it to cysteine 1. Oral = facilitates lysosomal transport and decreases tissue cysteine 2. Eye drops = oral cysteamine does not achieve adequate levels in ocular tissue 3. Early initiation of the drug can prevent or delay deterioration in renal function iii. GH – patients with growth failure that does not improve with cysteamine may benefit from GH iv. Kidney transplant – option for patients in renal failure v. BMTx
Investigation results (blood + urine) in RTA type I
Blood i. Non-anion gap (hyperchloraemic) metabolic acidosis ii. Hypokalaemia (due to hyperaldosteronism iii. Hyperammonaemia Urine i. Alkaline urine (pH >5.5) ii. HIGH urinary calcium iii. LOW urinary citrate a. Alkaline urine = due to impaired hydrogen ion excretion, urine pH cannot be reduced to <5.5, despite the presence of severe metabolic acidosis b. Hyperchloraemia = loss of sodium bicarbonate distally, owing to lac of H+ to bind to in the tubular lumen, results in increased chloride absorption and hyperchloraemia c. Hypokalaemia = inability to secrete H+ is compensated by increased K+ secretion distally, leading to hypokalaemia d. Hypercalciuria = usually present and can lead to nephrocalcinosis or nephrolithiasis e. Hypocitraturia = chronic metabolic acidosis impaired urinary citrate excretion; further increases the risk of calcium deposition in the tubules
RTA type I vs. type 2
Urine pH is < 5.5 (able to resorb HCO3 distally + excrete H+ distally) in proximal (type 2) Bicarb is higher in proximal type 2 Hypokalemia occurs in both – improves with therapy in distal, worsens in proximal Nephrocalcinosis a feature of distal RTA (type 1) Fanconi syndrome is a feature of proximal RTA (type 2) POSITIVE urine anion gap in type 1 Rickets more common in type 2
RTA type IV definition + causes
Decreased production or response to aldosterone in the collecting duct PRIMARY - Hypoaldosteronism - Addison’s - CAH - Pseudohypoaldosteronism SECONDARY - Obstructive uropathy - Pyelonephritis - Interstitial nephritis - Diabetes - Sickle cell nephropathy - ACEI, spironolactone, amiloride
Aldosterone - Secreted by - Acts on - Actions
Secreted by zona glomerulosa cells of the adrenal cortex Acts via mineralocorticoid receptor Acts on the principal cells of the cortical collecting tubule Increases reabsorption of Na - Increases no. ENAC channels luminal side - Increases Na/K/ATPase pump on basolateral side Increases excretion K+ - Reabsorption of NA from lumen creates luminal negativity which drive K+/ H+ secretion Increases excretion of H+
Features of Bartter’s Syndrome
**Biochemical features resemble those seen with chronic loop diuretic use** Hypokalaemia Hypochloraemia Metabolic alkalosis Normotensive hyperreninaemia Increased urinary excretion K Cl Na Ca Hypercalciuria
Clinical features of Bartter’s
Onset in first 2 yrs of life Often polyhydramnios + preterm labour if severe ‘antenatal’ variant Polyuria, polydipsia Vomiting Constipation Salt craving Dehydration FTT Fatigue / weakness / cramps Developmental delay Nephrocalcinosis
Bartter’s Syndrome pathophysiology
Defective reabsorption of NaCl in TAL LOH Distal tubular sodium sites overwhelmed = polyuria (resembles nephrogenic DI BUT urine osmolality often >100mosmol/L + responds to DDAVP) Polyuria + low serum Na = RAAS - Hypertrophy of JGA - Hyperaldosteronism = Na uptake + K excretion + H+ secretion distally - Exacerbates hypokalaemia + alkalosis Hypokalaemia stimulates PG = further NaCl wasting Unable to generate a POSITIVE potential in the tubular lumen due to reduced Na reabsorption = reduced Ca reabsorption
Bartter’s Syndrome genetics
Autosomal recessive Type I: NKCC2 transporter defect, antenatal Type II: ROMK transporter defect, antenatal Type III: ClC-KB transporter defect (no nephrocalcinosis), classic Type IV: Barttin defect, antenatal (deafness)
Treatment of Bartter’s Syndrome
Prevent dehydration Potassium supplementation Potassium sparing diuretics (spironolactone, amiloride) High sodium diet +/- Na supplementation Indomethacin (PGE inhibitor)
Biochem of Barterr’s vs. Gitelman syndrome
Barterr’s syndrome vs. Gitelman’s
Nephrogenic DI etiology
- Congenital
- Secondary
-
Congenital
- X-linked recessive disorder
- Most common pattern of inheritance of inheritance
- Many mutations – commonly mutation in AVPR2 gene (receptor for ADH)
- Autosomal dominant or recessive – 10% of cases
- Males and females equally affected
- Similar clinical phenotype as X-linked disorder
- Mutations in AVPR2 gene also identified
- X-linked recessive disorder
-
Secondary
- Not uncommon – seen in many disorders affecting renal tubular function
- Examples = obstructive uropathies, acute or chronic renal failure, renal cystic diseases, interstitial nephritis, nephrocalcinosis, or toxic nephropathy caused by hypokalaemia, hypercalcaemia, lithium or amphotericin B
- Defective aquaporin expression eg. Lithium intoxication
- Secondary ADH resistance – loss of the hypertonic medullary gradient as a result of solute diuresis or tubular damage resulting in inability to absorb sodium or urea
- Not uncommon – seen in many disorders affecting renal tubular function
Nephrogenic DI key features
Rare congenital or more commonly acquired disorder of water metabolism
Inability to concentrate urine even in the presence of ADH
Clinical manifestation nephrogenic DI
- Congenital
- Secondary
Congenital DI
- Present in newborn period with massive polyuria, volume depletion, hypernatraemia + fever
- Irritability and crying common feature
- Constipation and poor weight gain
- Developmental delay and mental retardation – due to episodes of hypernatraemic dehydratio
- Diminished appetite and poor oral intake – due to need to consume large amounts of water
- Behavioral problems – hyperactivity and ST memory problem
Secondary DI
- Present later in life
- Usually present with polyuria and hypernatraemia
- Associated symptoms such as dev delay and behavioral abnormalities less common
Inheritence + gene affected in congenital nephrotic syndrome (Finnish type)
- Autosomal recessive
- In utero inset of proteinuria
- Gene NPHS1 encodes for nephrin (Finish type)
- Gene NPHS 2 endodes for podocin - most common
- Gene NPHS3 endoce phospholipase epsilon - rare
Nephrogenic DI diagnosis
- Polyuria in a dehydrated child
- Hypernatraemia
- Serum osmolality > 290mOsm/kg with urine osmolality <600mosm/kg
- Lack of response to DDAVP
Treatment of nephrogenic DI
Denys Drash Syndrome
- Nuclear protein (WT1 mutation)
- Autosomal dominant
- Nephrotic syndrome
- Ambiguous genitalia
- Infant onset of steroid resistant nephrotic syndrome
- Wilm’s tumour
Peirson syndrome
- LAMB2 (GBM protein mutation)
- Nephrotic syndrome (mesangial sclerosis)
- Eye problems including microcoria
- Neurological anomalies
Indications for biopsy in nephrotic syndrome
- Atypical presentation or course
- Steroid resistance
- LOW C3
- Age <1yrs or >11yrs
Nephrotic range proteinuria
>3.5g / 24hrs
OR
urine protein: creat ratio > 2
Pentagon of clinical findings with nephrotic syndrome
- Hypoalbuminaemia
- Oedema
- Hypercholesterolaemia (due to increased lipoprotein synthesis by the liver in response to lipid + protein loss in the urine)
- Increased susceptibility to infection (cellulitis, spontaneous bacterial peritonitis + bacteraemia). Particularly encapsulated organisms. Due to loss of IgG + complement in urine.
- Hypercoagulability: vascular stasis, haemoconcentration, intravascular volume depletion, increase plt no, increase hepatic fibrinogen production, loss of antithrombin III + protein S in the urine.
Glomerular lesions associated with idiopathic nephrotic syndrome
Idiopathic nephrotic syndrome = ~90%
- Minimal change disease (85%); glomeruli appears normal or minimal increase in mesangial cells + matrix. Immunofluorescence microscopy negative. 95% respond to steroids.
- Focal segmental glomerulosclerosis
- Membranoproliferative glomerulonephritis
- C3 glomerulopathy
Complications of nephrotic syndrome
- Infection
- Thrombosis
- Hypothryoidism (loss of TGB in urine)
- Hypercholesterolaemia
- Poor growth
- AKI
- Vitamin D deficiency (due to loss in urine)
Treatment of nephrotic syndrome
- Steroids 1st line
- Steroid sensitive IF remision after < 4 weeks treatment
- Steroid dependent IF 2 consecutive relapses whilst on steroids OR within 14 days of ceasing
- Steroid resistant IF failure of remission after at least 4 weeks treatment
IF not responsive then…
- Calcineurin inhibitors (cyclosporine / tacrolimus)
- Rituximab
- MMF
- ACEI to reduce proteinuria
Congenital nephrotic syndrome
Nephrotic syndrome occur within the first 3 months of life
Infantile nephrotic syndrome
Nephrotic syndrome that occurs within the first 3-12 months of life
Kidney anatomy
Glomerulus anatomy