CONSULT ROUNDS: Distal RTA

Renal tubular acidosis was our discussion today. Always fun to discuss.
Hard to diagnose. Proximal vs dital RTA is sometimes a hard diagnosis to make.
Few take home points from today's discussion

1. Urine Ph is a good marker to see how well the kidney is doing. If you have a metabolic acidemic state with low ph and low bicarbonate and there is no Anion gap, the urine ph appropriately should be low around 5-5.5 to get rid of that acid. If that's the case, the kidney is safely acidifying the urine.  Hence the defect is either GI or proximal tubule( one caveat that you are giving bicarbonate and there is a thrushold reached and you are spilling the bicarb in the urine and make the ph alkaline)
2. There are many mechanism involved in the defects in a distal RTA( or acidification defect). Some people might even say, the problem starts in the proximal tubule since the ammonium genesis is happening there. Then the ammonium is transported to the distal tubule intercalated cells for removal in the urine. so the defect can be in any of these processes.
3. Distal RTA classically presents with low K, and nephrolithiasis(ca phos stones) since there is hypocitraturia and alkaline ph
4. There are three main types of distal RTA
     **Secretory defect:-This is probably the commonest defect and is due to an inability to create and maintain a H‡ gradient across the luminal membrane. The cause is unknown but likely defect in the H/K ATPase transported in the luminal side.This is usually referred to as the CLASSIC distal RTA, usually caused by Sickle cell disease, Sjorgen's syndrome, lupus. etc
     ** back leak:-The ability to secrete H‡ is retained, but the gradient is not maintained due to back diffusion.
 associated with amphotericin B therapy as the drug makes holes in the cell and back diffusion happens
     ** hyperkalemic voltage defect:-This is due to an inability to maintain a negative intraluminal voltage and thus promote H‡ (and K‡) secretion. Voltage-dependent dRTA has many features in common with type IV RTA, most notably the association with hyperkalaemia: the key difference between these two forms of RTA
is that patients with voltage-dependent dRTA cannot lower urine pH in response to systemic acidosis.

Causes are listed below

*** Hypokalaemic (classic dRTA)
Marfan syndrome/EDS
Fabry disease
Wilson's disease
Dysproteinaemia
Amyloidosis
Primary hyperparathyroidism
Vitamin D intoxication
Chronic pyelonephritis
Interstitial Nephritis
Lupus
Renal transplant rejection
Sjorgen's syndrome
Lithium
Analgesic abuse
Toluene
Sickle Cell disease
Calcineurin Inhibitors

*** Hyperkalaemic (voltage-dependent dRTA)
Urinary tract obstruction
Sickle cell disease
Amiloride
Triamterene
Calcineurin inhibitors