Urinalysis Flashcards
How do you take a mid-stream urine sample?
Drink lots of water so bladder is at least half full
Wash hands to avoid contamination
It is essential to have a morning sample to avoid orthostatic proteinuria
What is orthostatic proteinuria?
A benign condition caused by changes in renal haemodynamics.
Present in a minority of (2-5%) otherwise normal individuals.
It is caused by a period of prolonged standing.
What can cause proteinuria?
After physical exercise Fever Pregnancy UTI Abnormally high BP Nephrotic/Nephritic syndrome CKD
What does a urine dipstick tell you?
Urinalysis:
Dipstick proteinuria may suggest glomerular or tubulointerstitial disease.
Urine sediment with red blood cells and red blood cell casts suggests proliferative glomerulonephritis.
Pyuria and/or white cell casts suggest interstitial nephritis (especially if eosinophils are present in the urine) or urinary tract infection (UTI).
Spot urine collection for total PCR allows reliable estimation of total 24-hour urinary protein excretion. The degree of proteinuria correlates with the rate of progression of the underlying kidney disease and is the most reliable prognostic factor in CKD.
What is used to detect and identify proteinuria?
24-hour urine collection for total protein and creatinine clearance.
To detect and identify proteinuria, use urine ACR in preference, as it has greater sensitivity than protein:creatinine ratio (PCR) for low levels of proteinuria.
For quantification and monitoring of proteinuria, PCR can be used as an alternative. ACR is the recommended method for people with diabetes.
What should you do in patients with non-visible haematuria?
Patients in whom initial urinalysis reveals non-visible haematuria should have a urine culture performed to exclude a UTI.
If a UTI is excluded, two further tests should be performed to confirm the presence of persistent non-visible haematuria.
If non-visible haematuria persists then a urological review is required
When is proteinuria significant?
Low molecular weight proteins are filtered by the glomeruli and most of these filtered LMW proteins are reabsorbed.
Tamm–Horsfall glycoprotein (THP), also known as uromodulin, is a glycoprotein that is secreted by the renal tubules.
Up to 150 mg/day of uromodulin may be excreted in the urine, making it the most abundant protein in normal urine.
Proteinuria >150mg/day is abnormal and is an important feature of increased glomerular permeability and therefore of early renal disease.
The dipstick tests commonly used to test for proteins usually detect albumin.
Microalbuminuria (30-300mg/day) is an early feature of several renal diseases including diabetic nephropathy and other forms of glomerular or tubular diseases.
Why are ACEi or ARBs used in CKD?
The progression of CKD in diabetes can be managed by intensive diabetic control and BP management.
Progression of CKD can be slowed through the use of ACE inhibitors or ARBs independently of their effects on BP.
In type 1 diabetics ACE-I decreases albuminuria and reduce diabetic nephropathy, ARBs have been shown to reduce proteinuria.
In type 2 diabetics ACE and ARBs have been shown to reduce renal disease progression and decrease albuminuria.
In type 2 diabetics ACE-I has also been shown to reduce new nephropathy irrespective of whether they have high blood pressure or not. It is therefore considered that ACE-i/ARBs are “renoprotective”
MoA of ACEi and ARBs
ACE inhibitors inhibit the conversion of angiotensin I to angiotensin II, ARBs inhibit the angiotensin II receptor.
Angiotensin II is Vasoconstrictive and salt retentive which underlies its pathophysiology in high blood pressure.
In terms of renal dysfunction Angiotensin II preferentially acts on the efferent arterioles to maintain the hydrostatic pressure at the glomeruli.
RAS overactivation and increased glomerular pressure have been implicated in diabetic nephropathy, Inhibiting the production of or the action of angiotensin II can, therefore, reduce glomerular hydrostatic pressure.
What is eGFR?
This is creatinine-based estimate of glomerular filtration rate calculated in the laboratory.
It is an estimate and is prone to error in particular groups of patients
Which drug is stopped when the eGFR is less than 30?
Metformin
Why is atorvastatin preferred to simvastatin?
Increased risk of myopathy and rhabdomyolysis in patients taking amlodipine and >20mg of simvastatin
What is the gold standard test for proteinuria?
The gold standard test for checking protein levels in the urine is a 24hour urine collection. However, for convenience sake, we check Urine ACR or Urine PCR.
Urine ACR stands for Urine albumin creatinine ratio.
Urine PCR stands for urine protein creatinine ratio.
Why can you get an abnormal PCR?
Caveats: We may get abnormal values of urine ACR or PCR if the urine creatinine is too low or too high after a heavy protein meal.
Also, beware of false-positive results in very concentrated urine & similarly, false-negative results in very dilute urine.
