Category Archives: Renal

Renal tubular acidosis

Leaky tubules, shedding bicarbonate plus other things, leading to acidosis.

  • Type 1 is distal tubule, which does most of the reabsorbing.
  • Type 2 is proximal tubule, so similar but less severe.
  • Type 3 probably just a mixture of types 1 and 2!
  • Type 4 have high rather than low potassium, so clearly not a leakage issue. Related to aldosterone ineffectiveness.

Types 1 and 2 can present with growth failure, else the effects of hypokalaemia (profound muscle weakness) and acidosis (abdominal pain). Type 1 leads to progressive kidney disease, with the associated bone disease (rickets). May also end up with stones. Associated with sickle cell, Ehlers Danlos.

Type 2 usually Fanconi syndrome so leakage of amino acids, phosphate etc. Can be caused by Cystinosis, Wilson’s, hereditary fructose intolerance, poisoning.

Type 4 often related to drugs, but also Addison’s, urinary tract obstruction.


Dipstick testing is highly sensitive and picks up tiny amounts of protein (and blood) that isn’t necessarily of any concern.

A significant proportion of well people will have one or 2 pluses of protein on dip testing at any one time. More common with intercurrent illness.

Can happen with urine infection. Can happen with exercise.

Large amounts of protein loss can indicate nephrotic syndrome. PCR (or ACR) would typically be above 200.

Rarely PCR can be extremely high, but turns out not to be albumin but Tam Horsfall protein – can be ignored!

Fabry’s disease

Alpha-galactosidase defect, one of the lysosomal storage disorders, with accumulation in various tissues.

X-linked but females get disease, so not correct to call them carriers.

Classically, “pain attacks”, affecting the extremities. In the abdomen, can mimic appendicitis. Due to accumulation in nerves. Since nothing to really see on examination, easily misdiagnosed as functional.

Other features:

  • Renal impairment and failure.
  • Angiokeratomas – a more specific feature, but not always present, and seen in other lysosomal disorders.
  • Corneal changes
  • Cerebrovascular and cardiac problems



In children under 10, high BP is usually secondary to an underlying disease or condition. Primary hypertension increasingly recognised in older, obese children.

Do repeated measurements, ideally automated home BP monitoring, before diagnosing hypertension. Check manually as well as with automated device. Beware “white coat effect”, even if not clearly anxious.

Use appropriate cuff size – cuff should cover at least 75% of the upper arm from the acromion to the olecranon (should be sufficient space at the antecubital fossa to apply stethoscope!) .  An inappropriately small cuff will overestimate BP.

Long list of causes, so follow the clues.

Family history important, of course.


So needs thorough history and examination, including:

  • Fundi
  • Bruits, radiofemoral delay
  • Neck for goitre


Consider then end organ effects –

  • Proteinuria, high creatinine
  • Retinopathy
  • Left ventricular hypertrophy, cardiac failure
  • Abnormal tone and reflexes, cranial nerve deficits if severe


Depends on how high, whether other risk factors (diabetes, chronic kidney disease), symptoms and evidence of end organ damage.

Initially low salt diet, weight loss (if obese).  Remember other morbidities related to obesity.

Acute hypertension might need frusomide and/or nifedipine.

Long term treatment is only going to be started if no improvement with lifestyle measures. Target BP depends on risk factors, as above.

[2016 European Society for Hypertension guidelines]

Cobalamin related metabolic disorders

Amino acid homocysteine is converted to methionine (“remethylated”) – cobalamin is involved in some of these processes, folate metabolism also important.

Various disorders.

Variety of presentations, at different ages:

  • Neurological (central and peripheral)
    • Feeding difficulties, apnoea in babies
    • Seizures
    • Subacute combined degeneration of spinal cord (peripheral neuropathy, ataxia, incontinence)
    • Acute and/or chronic encephalopathy – hypotonia, regression
    • Neuropsychiatric problems
  • vascular problems (stroke/embolism)
  • bone marrow (megaloblastic anaemia, cytopenia) – folate related
  • Atypical HUS
  • Glomerulopathy


  • High homocysteine, usually
  • Vitamin B12 and folate, for differential
  • Methylmalonic acid (in urine)
  • Acylcarnitine
  • Methionine (usually goes low)


Start intramuscular B12 (hydroxocobalamin) as soon as samples collected, to prevent end organ damage.

Betaine should be started if high homocysteine with low methionine found, helps push conversion to methionine.


Autosomal recessive condition of high homocysteine in blood and urine, causing similar neurological problems, thrombosis, Marfanoid appearance, downward subluxing lenses.

Needs low methionine diet. Betaine supplements help.

Fractional excretion

Used to work out whether biochemical abnormalities are due to renal dysfunction. There is not really a “normal range” for sodium and potassium in the urine, because it depends whether the body is trying to retain or excrete at any given time. So urinary sodium can be undetectable in dehydration, for instance.

Since creatinine is filtered passively, you can compare how much sodium/potassium is being excreted with what you would expect, by calculating:

Sodium excretion (Urinary Na/Plasma Na), divided by creatinine clearance (urinary creatinine/Plasma creatinine). Multiply by 100 to get a percentage.

Note that creatinine in plasma is usually measured in micromoles, and in urine in millimoles. Online calculator here:

If sodium low, you expect the kidneys to retain, so fractional excretion should be less than 1%. For low potassium, fractional excretion should be less than 10%. The opposite is true for high values.

Even where plasma sodium normal, fractional excretion can give you a clue to kidney disease – 1-4% suggests intrinsic renal pathology, over 4% post-renal.

Renal causes of low sodium/potassium include renal tubular acidosis (various forms), Bartter’s syndrome. Non-renal causes include GI losses (eg pyloric stenosis), Pseudo-Bartter’s syndrome (eg CF).

An alternative, possibly simpler method is transtubular potassium gradient (TTKG) :

TTKG = urine potassium/(plasma osmolality/urine osmolality)/serum potassium

For this formula to be accurate urine osmolality should be higher than plasma osmolality and urine sodium should be greater than 25 mEq/L.

Individuals with hyperkalemia should have a TTKG above 10. Values below 7 are consistent with mineralcorticoid deficiency, especially if accompanied by hyponatremia and high urine sodium concentration.

Individuals with hypokalemia should have TTKG values below 2.

Autosomal dominant polycystic kidney disease

ADPKD – previously Adult PCKD but now recognized as having manifestations in childhood.  Cf Autosomal recessive disease, severe, renal failure in infancy.

1 in 400 to 1,000 live births, making it the most common monogenic cause of renal failure. The typical age of onset is in middle life, but the range is from infancy to 80 years.  Associated with liver cysts (asymptomatic) and intracranial aneurysms. 10-25% do not have family history (de novo mutations, missing records or mosaicism).

Possible presenting symptoms of renal disease in children with ADPKD are frequency, nocturia and/or, hematuria, urinary tract infection(s) and back, flank or abdominal pain. Often, the earliest symptoms are polyuria and polydipsia, from decreased urinary concentrating ability.

Extrarenal manifestations seen esp hypertension (renin angiotensin system, sodium retention, endothelial dysfunction), also liver cysts (asymptomatic), intracranial cysts and valvular defects but these are only seen in adults. 25% of children are hypertensive by the time they reach adolescence.  (GFR stays stable until around 40yrs, then rapid decline, about 50% have ESRF by 60yrs).

Importantly, children who were diagnosed in utero or within their first 18 months of life, the so-called VEO group, represent a particularly high-risk group of ADPKD patients and should be managed accordingly.  Diagnostic imaging criteria not validated under 15yrs, genetic testing also challenging.

Recommendation from Kidney Disease Improving Global Outcomes (KDIGO) Consortium against screening children for APCKD.  [Also highlight variety of different cystic disorders in children, so recommend thorough clinical assessment for extrarenal manifestations in case syndrome eg Von Hippel Lindau, USS of parents and/or grandparents if negative family history, and USS to look for dysplastic kidneys, glomerulocystic disease, and tuberous sclerosis complex].[Kidney international 2015]

Increasing evidence that hypertension, left ventricular hypertrophy (even between 75th and 95th centile for BP) and increased kidney volume predates symptoms in affected children.  A study of early use of ACE inhibitor halted progression of LVH and fall in renal function.  Adding pravastatin reduced progression of structural kidney disease.  Disease modifying drugs in development.  [BMJ 2016;353:i2957 Editorial, GOS, Birmingham, Evelina].  “We propose an urgent national debate on an improved inclusive approach involving patients and their families and a range of clinicians, ethicists, and commissioners. A few pounds spent now on screening and early intervention could save many thousands later by delaying hypertensive complications and chronic kidney disease.”

Potential for pre-implantation genetic diagnosis.  See Ethics.

Only one drug known to have moderate effect on disease progression in adult ADPKD patients, vasopressin V2 receptor antagonist tolvaptan (recent Cochrane review).  But timing of use unclear.

Psychological impact of having genetic disease that can be passed on to children very common in adult patients.  But a benefit of diagnosis is potential to target modifiable risk factors  – children with normal BP have slower cyst growth.  And knowledge can give sense of control over life decisions, esp reproductive decisions.

Posterior urethral valves

1 in 5000 births.  Mostly failure of Wolffian duct development, rarely failure of urethral canalisation.

2/3 detected antenatally, with distended bladder. If missed, then present with urinary tract infection, abnormal voiding (dribble rather than fountain!) else incontinence (if toilet trained, of course).

Later detrusor failure, tubular dysfunction, renal failure.

Renal investigations


Renal uss image anotated

Incomplete bladder emptying cannot be diagnosed on a single post-void residual urine on ultrasound, due to significant intra-individual variability. Two post-void residual urine tests are recommended; larger volumes are seen if the bladder has been over distended (eg initial volume greater than 115% of expected), and in younger children. Greater than 20 ml is more specific than 10% bladder capacity. [J urology 2009 (182):1933]

Bladder capacity is = (Age +1) x 30 (ml) max 390ml.



In a study of 342 kids with asymptomatic microscopic haematuria, no cause was found in the large majority of patients. The most common cause discovered was hypercalciuria (16% of patients) followed by post–streptococcal glomerulonephritis (1%). No evidence for value of early detection of hypercalciuria (may be at long-term risk for nephrolithiasis and bone demineralization).  The children with asymptomatic post–streptococcal glomerulonephritis all improved spontaneously and without complication.  None had evidence of urinary tract infection! Clinically insignificant abnormalities in the upper urinary tracts of 5 children and grade 3 reflux in 1  [Arch Pediatr Adolesc Med. 2005;159(4):353-355. doi:10.1001/archpedi.159.4.353]

Asympt recurrent can be monitored for 5yr!


  • frank blood,
  • protein,
  • hypertension,
  • other features (joints, rash, wt loss)

Haematuria defined as persistent dipstick positive on at least 3 occasions for at least 3 months. Else as >2rbc per HPF (not same as flow cytometry). Then consider:

  • Red cells or not?
    • myoglobinuria = haemolysis
    • beetroot!
    • Porphyrins, other unusual pigments
  • Proteinuria or not?

If spot urine abnormal, repeat on early morning urine and then proceed to 12-14hr collection. Urine calcium/creatinine has age specific normals, high at birth (up to 1.5 in toddlers) falling to adult max of 0.7 at age 7. High levels especially significant in the presence of a normal plasma calcium

Investigations – only do bloods if macroscopic or nephritis suspected:

  • Do urine culture and microscopy.
  • Do PCR if proteinuria.
  • If macroscopic, do FBC, U&Es, LFTs, Coag.
  • Renal USS
  • Screen family members with urinalysis
  • Spot urine calcium/creatinine
  • If acute nephritis, do C3/4, ASOT, immunoglobulins, ANCA, anti GBM as below.
  • If stones suspected, do 2 sets of spot urine Ca/creat, Oxalate/creat, Urate, amino & organic acids, pH, KUB.

Differential is:

  • Tumour – bladder (colour changes during voiding, dysuria with sterile culture) or kidney
  • IgA nephropathy – persistent, progressive in 30%, diagnosis on biopsy
  • Alports – usually X dominant, deafness in minority, cataracts in 10%
  • Sickle cell – 1% macroscopic, 16% microscopic. Papillary necrosis, usually painless, episodic. May progress to sickle nephropathy.
  • Venous thrombosis – esp neonates, nephrotics.
  • Vascular – AVM, Nutcracker syndrome (compression of the left renal vein between the abdominal aorta and SMA)
  • Nail-patella syndrome (BM disorder, like Alports)
  • Polycystic Kidney Disease

Biopsy if persistent high grade microscopic, or microscopic with proteinuria (>150 mg/24 hr)/hypertension/impaired renal function, or 2 episodes of gross haematuria. Cystoscopy for bladder problem.