## Medicine

### Kidney

Question
6 out of 6

Fanconi syndrome occurs in which type of RTA? (LQ)

 A Type I B Type II C Type IV D All of the above

Ans. B Type II
 Table 265-2 Comparison of Normal Anion-Gap Acidoses (Ref, H 16th Pg1699) Finding Type 1 RTA Type 2 RTA Type 4 RTA GI Bicarbonate Loss Normal anion-gap acidosis Yes Yes Yes Yes Minimum urine pH >5.5 <5.5 <5.5 5 to 6 % Filtered bicarbonate excreted <10 >15 <10 <10 Serum potassium Low Low High Low Fanconi syndrome No Yes No No Stones/nephrocalcinosis Yes No No No Daily acid excretion Low Normal Low High Urine anion gap Positive Negative Positive Negative Daily bicarbonate replacement Needs <4 mmol/kg >4 mmol/kg <4 mmol/kg Variable

Extra Edge: The "urine anion gap" is principally used to determine whether the kidneys are capable of appropriately acidifying urine.

## Calculation

i. Urine anion gap is calculated by subtracting the urine concentration of chloride (anions) from the concentrations of sodium plus potassium (cations): where the concentrations are expressed in units of milliequivalents/liter (mEq/L).

= Na+ + K+ − Cl

ii. In contrast to the serum anion gap equation, the bicarbonate is excluded. This is because urine is acidic, so the bicarbonate level would be negligible.

iii. Normal urine anion gap is zero or slightly positive.

Uses

Urine anion gap is an 'artificial' and calculated measure that is representative of the unmeasured ions in urine. Usually the most important unmeasured ion in urine is NH4+.

A. A positive urine anion gap suggests a low urinary NH4+ (e.g. renal tubular acidosis).

A negative urine anion gap suggests a high urinary NH4+ (e.g. diarrhea).

Summary of Renal tubular acidosis

Type IV = K

II = K, Fanconi syndrome

I = K, urine pH > 5.5, Renal stone, Urinary citrate is reduced.

Fanconi syndrome

i. The proximal tubule is responsible for reabsorption of many solutes, including 50% of filtered sodium, most bicarbonate and all filtered glucose and amino acids.

ii. Fanconi syndrome is a disturbance of proximal tubule function, with defective reabsorption of amino acids, K+, phosphate (leading to hypophosphatemic rickets and osteomalacia), glucose (glycosuria) and bicarbonate (Type 2 RTA).

iii. There is polyuria (due to osmotic diuresis), and hypokalemia (Na delivery to distal tubules leads to exchange).

iv. Causes:

A.Idiopathic

B. Inherited: Errors of metabolism egcystinosis, fructose intolerance, galactosemia, glycogen storage disease, Wilson's disease, Lowe's syndrome, tyrosinemia.

C. Acquired:

b. Drugs (out. of-date tetracycline),

c. Light chains (myeloma, amyloidosis),

d. Immunological (interstitial nephritis, transplant rejection).

Features: dehydration, failure to thrive. Vitamin D resistant rickets is typical.

There may be progressive renal failure in early adulthood.

Treatment: Remove any cause and replace losses. K+, sodium bicarbonate, and vitamin D supplements are used