Nephrology - Passmedicine Flashcards
How do you calculate an anion gap?
(Na + K) - (bicarb + Cl)
What is considered a normal anion gap?
8-14mmol/L
What are the two types of metabolic acidosis?
Normal anion gap (aka. hyperchloraemia) metabolic acidosis
Raised anion gap metabolic acidosis
List causes of a normal anion gap (aka. hyperchloraemia) metabolic acidosis
GI bicarbonate loss - diarrhoea, ureterosigmoidostomy, fistula Renal tubular acidosis Drugs, e.g. acetazolamide Ammonium chloride injection Addison's disease
List causes of a raised anion gap metabolic acidosis
Lactate: shock, hypoxia Ketones: DKA, alcohol Urate: renal failure Acid poisoning: salicyclates, methanol 5-oxoproline: chronic paracetamol use
What is the anion gap?
Measure of the difference between cations and anions
If the serum is neutral in charge why does an anion gap exist?
We are only measuring 4 ions to calculate it (there are a lot of significant anions not included, e.g. phosphate, negatively charged plasma proteins e.g. albumin)
What does a high anion gap mean?
The negatively charged ions and proteins (not accounted for) are taking up a larger proportion of the serums negative charge than usual
What causes a high anion gap?
Increased organic acid in the blood, e.g. lactate anions
Explain why there is an increased anion gap in lactic acidosis
Lactic acid breaks down into lactate and H+, H+ is buffered by bicarb so there is less bicarb and more of the negative proportion of the serum being made up by lactate so the anion gap is increased
What essentially causes a normal anion gap?
Bicarbonate loss
Kidneys compensate by reabsorbing more Cl keeping serum electroneutral
What is the most common cause of bicarbonate loss causing normal anion gap?
Diarrhoea
Then renal tubular acidosis
Does vomiting cause a metabolic acidosis?
Usually no
You are losing H+ ions in gastric acid
Define acute interstitial nephritis
Pattern of kidney inflammation localised to the kidney tubulo-interstitial space
What tends to trigger acute interstitial nephritis?
Medications, esp. antibiotics
What antibiotics commonly cause acute interstitial nephritis?
Penicillin Rifampicin NSAIDs Allopurinol Furosemide
What are causes of acute interstitial nephritis other than medications?
Systemic conditions - SLE, sarcoidosis, Sjogrens
Infections: Hanta virus, staphylococcus
What do you see on histology in acute interstitial nephritis?
Marked interstitial oedema and interstitial infiltrates in the connective tissue between renal tubules
What are the clinical features of acute interstitial nephritis?
Fever, rash, arthalgia
Eosinophilia
Mild renal impairment
HTN
What can you see on investigation in acute interstitial nephritis?
Sterile pyuria
White cell casts
Raised urea and Cr
Who does tubulointerstitial nephritis with uveitis tend to affect?
Young females
What are features of tubulointerstitial nephritis with uveitis?
Fever
Wt loss
Painful, red eye
Urinalysis shows leukocytes + protein
How do you manage acute interstitial nephritis?
Usually managed by stopping the offending medication
What is the most common cause of a nephrotic syndrome in children/young people?
Minimal change disease
What causes the majority of cases of minimal change disease? What are other causes?
Idiopathic mostly
Drugs: NSAIDs, rifampicin
Hogdkin’s lymphoma, thymoma
Infectious mononucleosis
What is the pathophysiology of minimal change disease?
T-cell + cytokine mediated damage to the glomerular basement membrane –> polyanion loss
Resultant reaction of electrostatic charge –> increased glomerular permeability to albumin
What are the features of minimal change disease?
Nephrotic syndrome
Normotension usually
Highly selective proteinuria (only medium sized proteins (e.g. albumin and transferrin) leak
What investigation will confirm a diagnosis of minimal change disease?
Renal biopsy
What will you see on electron microscopy of the renal biopsy in minimal change disease?
Fusion of podocytes + effacement of foot processes
How is minimal change disease managed?
80% corticosteroid responsive
If steroid resistant –> cyclophosphamide
What is the prognosis of minimal change disease?
1/3rd –> 1 episode
1/3rd –> infrequent relapses
1/3rd –> frequent relapses which stop before adulthood
What is a nephrotic syndrome?
Damage to glomeruli allows leakage of proteins into urine –> proteinuria
Albumin leaving blood –> hypoalbuminaemia –> low oncotic pressure –> oedema
Unknown process –> hyperlipidaemia (which can also leak into urine)
What are the 4 hallmarks of nephrotic syndrome?
Proteinuria
Hypoalbuminaemia
Oedema
Hyperlipidaemia/lipiduria
What are the 3 layers of the glomerulus?
Endothelial cells (which line capillaries), basement membrane, podocytes
What are podocytes named podocytes?
They have foot like processes
How are the podocytes charged?
Negatively - helps them repel plasma proteins (e.g. albumin) and therefore podocytes act as a charge barrier
What happens in minimal change disease that means that proteins can leak into bowen’s capsule?
T-cells release cytokines which specifically damage the foot processes of podocytes making them flatten out (effacement) –> reduced charge barrier and albumin can slip into nephron
NB larger proteins, e.g. Ig aren’t allowed through
What technique do you need to see foot effacement in minimal change disease?
Electron microscopy
What is acute tubular necrosis?
Ischaemic/nephrotoxic injury to the kidney which leads to cell death
What area is most prone to AKI and why?
Renal medulla (it is relatively hypoxic making it prone to renal tubular hypoxia)
What is the best indicator of renal function?
eGFR
What parameters are required to estimate eGFR?
Serum creatinine, age, race, gender, body size
What sort of things may cause an AKI?
Nephrotoxic stimuli, e.g. aminoglycosides, contrasts –> apoptosis
Myoglobulinuria (e.g. after compartment syndrome) + haemolysis –> necrosis
What patients are more likely to be affected by post-op renal failure?
Early pts, with PVD, high BMI, COPD, on vasopressors or nephrotoxic medications
Avoiding hypertension/hypotension will reduce the risk of renal tubular damage
Hypotension
What is a typical history of acute tubular necrosis?
Worsening renal function
Muddy brown casts
What are the three types of AKI?
Prerenal - cause before kidneys
Intrarenal - cause within kidneys
Post-renal - cause after kidneys
When is rhabdomyolysis typically seen?
After a fall or prolonged epileptic seizure
May be in those who have AKI on admission
What are features of rhabdomyolysis?
AKI with disproportionately raised creatinine Elevated CK Myoglobulinuria Hypocalcaemia Elevated phosphate Hyperkalaemia Metabolic acidosis
Why do you get hypocalcaemia in rhabdomyolysis?
Myoglobin binds calcium
Why do you get elevated phosphate in rhabdomyolysis?
As it is released from myocytes
Why do you get hyperkalaemia in rhabdomyolysis?
Secondary to renal failure
What can cause rhabdomyolysis?
Seizure Collapse/coma Ectasy Crush injury McArdle's syndrome Drugs - statins, esp. if co-prescribed with clarithromycin
How is rhabdomyolysis managed?
IV fluids (normal saline) to maintain good urine output Urinary alkalinization is sometimes used
What is used as a diagnostic criteria in rhabdomyolysis?
CK >5x normal
How is Alport’s syndrome inherited?
X linked dominant
What genetic defect causes Alport’s syndrome?
Defect in gene which codes for IV collagen –> abnormal glomerular basement membrane
When does Alport’s syndrome tend to present?
Childhood
What are features of Alport’s syndrome?
Microscopic haematuria Progressive renal failure Bilateral sensorineural deafness Lenticonus Retinitis pigmentosa
What is lenticonus?
Protrusion of the lens into the anterior chamber
What do you see on renal biopsy in Alport’s syndrome?
Splitting of the lamina dense on electron microscopy (basket weave appearance)
How is Alport’s syndrome diagnosed?
Molecular genetic testing
Renal biopsy
At what K level should you give calcium gluconate etc. to treat hyperkalaemia?
> 6.5 OR ECG changes
What biochemical pattern is more characteristic of dehydration as opposed to AKI?
Raised urea and cr but urea is proportionately more raised
Hypernatraemia
Is eGFR more inaccurate in high or low muscle mass?
Both - it is most inaccurate at extremes of muscle mass
What are causes of transient non-visible haematuria?
UTI
Menstruation
Vigorous exercise
Sexual intercourse
What are causes of persistent non-visible haematuria?
Cancer (renal, bladder, prostate) Stones BPH Prostatitis Urethritis Renal causes - e.g. IgA nephropathy
What things may mimic haematuria but no blood is actually in the urine?
Foods - beetroot, rhubard
Drugs - rifampicin, doxorubicin
What is the test of choice for haematuria?
Urine dipstick
Define persistent non-visible haematuria
Blood in 2/3 samples tested 2-3 weeks apart
Which patients with haematuria should be urgently referred (within 2 weeks)?
Age >=45 AND unexplained visible haematuria in absence of UTI or visible haematuria that persists/recurs after treatment of UTI
Age >= 60 AND unexplained non-visible haematuria and either dysuria or raised WCC on blood test
Which patients with haematuria merit a non-urgent referal?
Age >=60 with recurrent or persistent unexplained UTI
Do patients under 40 with haematuria, with normal renal function, who are normotensive and have no proteinuria need to be referred?
No - they can be managed in primary care
Which test is most useful in distinguishing between acute tubular necrosis and prerenal uraemia?
Urinary sodium
What age group is HUS typically seen in?
Young chlidren