Renal Tubular Acidosis Flashcards
What normally happens to urine pH under acidic conditions usually?
What is the pH doing in proximal RTA? In distal RTA?
Normal response is to acidify urine to pH under 5.5
In proximal RTA, urine pH is borderline where it should be ie 5
In distal RTA, pH is over 5.5, often about 6.5
Note urine anion gap is positive and urine ammonium LOW in all types of RTA
Type 1 RTA
- where is the defect
- what is the main mechanism where the person becomes acidotic
- how does the person become hypokalaemic
- what is the urine pH
- what are the other clinical features
- what is the confirmatory test
Defect in the intercalated (alpha cells) of collecting tubule–>decreased H secretion
H builds up in the blood
Potassium is excreted instead of H
Urine pH is high (over 5.5)
See hypercalciuria
Get renal calculi- high ca with low citrate promote stones
Confirm with Ammonium chloride acidification test- see if can acidify urine
Treat with sodium bicarb or sodium citrate; citrate more expensive but inhibits stone formation
Bone disease is common
Causes of Type 1 RTA?
Idiopathic/sporadic
Familial : AD, AR mutation in H-ATPase and AE1 gene, Associated with SN deafness.
Autoimmune (SLE, Sjogrens, RA) Hereditary hypercalciuria, hyperPT, Vitamin D intox Thyroid disorders Hypergammaglobulinaemia Drugs (Ambisome, Lithium, Ifosfamide, and PPIs can exacerbate a defect) Chronic hepatitis Obstructive uropathy Sickle cell Renal transplant
Causes of Type 2 RTA?
Primary: idopathic, sporadic, Wilsons disease, familial
Fanconi syndrome
Acquire: MM, radiological contrast, antivirals (tenofivir, adenovir), aminoglycosides, rhabdo, heavy metal poisoning, amyoidosis, interstitial nephritis (eg CMV, polyoma, drugs_)
Type 2 RTA
- where is the defect
- what is the main mechanism where the person becomes acidotic
- what is the urine pH
- what are the other clinical features
- what is the confirmatory test
Failure of proximal resorption of HCO3
Acidosis in the blood is milder than distal (HCO3 12-20)
Urine pH varies with serum HCO3 (pH under 5.5)
May need to treat with high dose HCO3
Often assoc with generalised proximal tubule dysfunction (Fanconi syndrome)
Potassium is normal or low
Normal urine Ca
Do not get nephrocalcinosis
Bone disease is common
Confirm test is fractional excretion of bicarbonate >25%
What are the features of Fanconi syndrome?
Generalised proximal tubule dysfunction Lose phosphate, uric acid, glucose, amino acids Low serum phosphate Low urine urate Glucose in urine Normal serum glucose
Causes of Fanconi syndrome
MM, MGUS Wilsons Expired tetracyclines Tenofovir Lead poisoning
Type 4 RTA
- where is the defect
- what is the main mechanism where the person becomes acidotic
- what is the urine pH
- what are the other clinical features
- what is the confirmatory test
Aldosterone deficiency OR distal tubule resistance to aldosterone–> decrease in Na absorption
Decrease in H and K secretion–>hyperkalaemia and acidosis
Urine pH less than 5.5
Urine calcium is normal or low and not associated with bone disease
Impaired ammonium production
Treat with dietary restriction of sodium and frusemide
Causes of type IV RTA?
Renin decrease in: diabetic nephropathy, interstital nephritis
Normal renin but decreased aldosterone in: ACE, ARBs, heparin, primary adrenal response
Reduced response to aldosterone in:
- medications -spironolactone, TMP-SMX, tac, pentamidine
- tubulointerstitial disease- sickle cell, SLE, amyloid, DM
When would you consider RTA as the diagnosis?
Would consider when normal anion gap metabolic acidosis and no obvious GI cause (the urine anion gap will be POSitive and consistent with a non-gut cause with a neGUT ive urine anion gap).
Potassium can be high or low in these disorders.
How do you calculate the urine anion gap?
Na + K - (Cl)
The Cl mirrors the ammonia
NH4 increases in metabolic acidosis if renal acidification is intact as NH4Cl
Often not needed if there is clinically obvious diarrohea, but positive or zero UAG in RTA, neGUTive UAG in GI causes of NAGMA.
How do you correct a plasma anion gap for albumin low?
.25 x albumin- add to AG
How would the plasma potassium help you tell between RTAs?
High in type 4
Normal/low in type 1,2
How does the urine calcium help you tell between RTAs?
High urine calcium in type 1 RTA, assoc with nephrocalcinosis
The others are not
Which RTAs give you bone disease
Proximal, and often distal
