Remember

FeNa> 2% = intrinsic renal disease i.e acute tubular necrosis or acute interstititial nephritis

In prerenal azotemia e.g due to dehydration, FeNa is <1%, urine sodium is <20mEq/L, urine osmolality> 500mEq/L
Kidney reabsorbs Na and water to compensate for the hypovolaemia or hypotension.

Renal tubular acidosis

 common USMLE topic

Non anion gap metabolic acidosis


Type 1:
Distal RTA
Failure of H+ secretion by the α intercalated cells of distal tubes
There's hypokalaemia
Met. acidosis is severe, more alkaline urine >5.3
May be associated with urolithiasis , rickets

Type 2:
Proximal RTA.
e.g Fanconi syndrome (prox tubular cell dysfunction)
Failure of  HCO₃⁻ reabsorption from the urine by the proximal tubular cells
There's hypokalaemia. Also associated with rickets
Met acidosis is less severe because distal tubular function is normal. urine PH<5.3

Type 4:
No aldosterone (Addisson's disease,ACEIs,ARBs,DM nephropathy,Sickle cell nephropathy)
or
Na/K pump not responding to aldosterone (NSAID nephropathy,CKD,)
There's hyperkalaemia, hyponatremia, hyperchloraemia
urine PH<5.3. . Met. acidosis is mild

Wegener granulomatosis

Upper resp disease + lower resp disease, + glomerulonephritis
Other signs of vasculitis on skin,eyes, joints etc

Best initial: c-ANCA
most accurate test: biopsy
(lung biopsy best)

Tmt: Prednisone +cyclophosphamide.



note: Good pasture has similar presentation but no upper resp involvement and anti GBM abs r present (Best initial test).
kidney biopsy shows linear deposits. No signs of systemic vasculitis unlike in Wegener's granulomatosis.

Intussusception

2yr old Child with abdo pain
presents with features of small bowel obstruction

red currant jelly stool

sausage shaped abdo mass

USS shows target sign (one tube inside another)

Air contast enema both diagnoses and reduces it in most cases

Renal cell CA

Adult with gross painless hematuria, think of malignancy: bladder, renal, ureters
Do Contrast Abdo CT or IVU
If nothing is seen, do cystoscopy.

Note: Bladder  mass more common than renal cell CA

Renal cell CA:
hematuria, flank pain , abdo mass in 10%. Presence of lft sided varicocoele which doesn't empty when recumbent, is highly suggestive of RCC.

Nephrotic Syndrome

Anarsaca
periorbital edema
hypoalbuminemia
hyperlipidemia
hyperproteinuria >3.5g/day,
hypertension
Thrombosis (due to loss of protein c  & s and antithrombin)
Infections (Ig loss)

Initial test : Urinalysis
Most accurate for cause : Biopsy
Most accurate measure of proteinuria: Urine albumin/creatinine ratio = 24hrs urinary protein

Children : think minimal change dx
Adults : most common is focal segmental (initially membranous glomerulonephritis)
AIDS: think focal segmental

Renal Biopy done in Adults
Biopsy not reqd in children with suspected NS, treat empirically with prednisone. + cyclophosphamide if resistant