Renal disease and clinical syndromes

Typically presents with one or more of rather a short list of clinical syndromes—listed from 1 to 7 below.

One underlying pathology may have a variety of clinical presentations.

• Proteinuria and nephrotic syndrome: 

Drawn below are the barriers that keep protein and blood cells out of the urine. These are the endothelial cell, basement membrane and epithelial cell (podocyte). The epithelial cell (podocyte) seems to be most important. Injury to these barriers causes protein and blood to leak into the urine.

Proteinuria results when there is a weakness in the filter vessel  wall that allows protein to leak into the urine.

• Normal protein excretion is <150mg/d.
• This may rise to ~300mg/d—eg orthostatic proteinuria (related
  to posture), during fever, or after exercise.
• Proteinuria (excessive protein excretion) is a sign of
  glomerular or tubular disease.
• Nephrotic syndrome (p290) is the triad of proteinuria
  (>3g/d), hypoalbuminaemia (albumin <30g/L) and oedema.

• Haematuria and nephritic syndrome: 

Causes of haematuria

• Blood in the urine may arise from anywhere in the renal tract.
• It may be macroscopic (visible to the naked eye) or microscopic  (found on dipstick testing and microscopy).
• Haematuria with dysuria is usually from a UTI.
• Painless haematuria is more ominous, eg bladder or other GU cancer (eg if >40yrs old, esp if a smoker) or glomerulonephritis.
• Nephritic syndrome comprises haematuria and proteinuria—often
  with hypertension, pulmonary and peripheral oedema, oliguria (urine
  output <400mL/d), and a rising plasma urea and creatinine.
• The question of who to refer haematuria patients to (urologist or nephrologist) is answered on p278. 

• Renal pain and dysuria:
• Renal pain is usually a dull and constant and in the loin.
• It may be due to 
• renal obstruction (look for swelling ± tenderness), 
• pyelonephritis, 
• acute nephritic syndrome, 
• polycystic kidneys, or 
• renal infarction.
• Renal (ureteric) colic is severe waxing and waning loin pain radiating to groin or thigh eg with fever and vomiting.
• It is caused by 
• renal stone, 
• clot, or 
• sloughed papilla. 
• Urinary frequency with dysuria (pain on voiding) suggests a
  UTI. 

• Oliguria and polyuria:
• Oliguria is a urine output of <400mL/d—a normal response to hot climates or fluid restriction.
• Pathological causes: 
• renal perfusion↓, 
• renal parenchymal disease, 
• renal tract obstruction.
• Polyuria is the voiding of abnormally high volumes of urine
• Causes
• high fluid intake
• diabetes mellitus,
• diabetes insipidus (p224), 
• hypercalcaemia, 
• renal medulla disorders (urine concentration is impaired),
• SVT (p112). 

• Acute renal failure (ARF) is significant decline in renal function occurring over hours or days, detected by a rising plasma creatinine (± oliguria).
• ARF usually occurs secondary to
• circulatory dysfunction 
• hypotension, 
• hypovolaemia, 
• sepsis
• urinary obstruction.
• Primary renal disease is a less common cause. 

• Chronic renal failure (CRF) or chronic kidney disease (CKD) is defined as irreversible, substantial, and long-standing loss of renal function.
• It is classified according to glomerular filtration rate (GFR): see p661.
• There is often a poor correlation between symptoms and severity of CRF.
• Progression may be so insidious that patients attribute symptoms to age or a minor illnesses.
• Current guidelines advise nephrology referral if 
• CKD stage ≥3 (p661), ie GFR <60mL/min, 
• other features are present:
• GFR is falling progressively
• Microscopic haematuria
• Urine protein:creatinine ratio (PCR)↑, p301
• Unexplained anaemia, hyperkalaemia, or calcium or phosphate imbalance
• Suspected systemic illness (eg SLE)
• BP uncontrolled despite taking 3 drugs.
• Refer urgently if GFR 15-29 (same-day if <15) even if no other features present. 

• Silence:
• Serious renal failure may cause no symptoms at all.
• This is why we do U&Es before surgery and other major  interventions.
• This reminds us not to dismiss odd chronic symptoms such as fatigue or ‘not being quite with it’—without doing a blood test.
• Microalbuminuria is a famously silent harbinger of serious renal and cardiovascular risk.
• It is described on p306.
• In one study, 30% of those with type 2 diabetes mellitus died
  within ~5 years of developing microalbuminuria.