Renal Flashcards
Which differential should you suspect in a patient who is over 60 and presents for the first time with renal colic?
Ruptured AAA
What is orthostatic proteinuria?
A benign condition caused by changes in renal haemodynamics.
MOA: A period of prolonged standing occurs, the patient then tests positive for protein in their urine.
Present in 2-5% of normal individuals.
How should a mid stream urine sample be collected? What needs to be done?
- Collect the sample early in the morning, preferably the first urination of the day:
Most concentrated sample, the elements are better detected. - Drink fluids before hand - to fill your bladder, test is most accurate when bladder is half full
- Wash your hands well beforehand - to avoid contamination
- Clean the area only if:
- you have recently opened your bowels
- you have just finished your period - Place the jar close to your urethral opening
- Don’t collect the first bit of urine, collect from after the stream hits the toilet
- Place the lid tightly on the sample jar, without touching the inside of the jar.
What does urine analysis tell us in chronic kidney disease?
DIPSTICK:
1. Proteinuria - suggests glomerular or tubulointerstitial disease
- Urine sediment with Haematuria/red blood cell casts - suggests proliferative glomerulonephritis
- Pyuria or white blood cell casts - suggests interstitial nephritis or UTI
Which mode of urine collection has the greatest prognostic value in CKD?
The two options:
Spot urine collection and 24 hour collection.
Spot urine collection for total protein is the best (relative to 24 hour collection):
It is a one off test - a single sample is used.
In a 24 hour collection, urine is collected throughout the day in a single container - an averaged result.
Which test has greater sensitivity for low levels of protein in the urine? ACR or PCR?
In short: ACR = microalbuminaemia (DM)
PCR = proteinuria (CKD)
ACR has greater sensitivity for low levels of proteinuria (microalbuminaemia)
PCR is better for quantification/monitoring proteinuria
What further testing does urine dipstick positive for haematuria indicate for?
Anyone with non-visible haematuria should have urine culture performed to exclude UTI.
If persistent non-visible haematuria: urology referral
Since diabetes is the leading cause of CKD, what should be checked at the annual DM checkup in GP?
BP Urine dipstick BMI Diabetic foot exam HbA1c Serum creatinine and eGFR Serum cholesterol QRISK3 - quantify CV risk
What is the upper limit of normal blood sugar in HbA1C?
HbA1C:
42 mmol/Mol is the upper limit
48mmol/Mol is considered diabetes
Fasting:
5.5 mmol/L is the upper limit
7 mmol/L is considered diabetes
How is chronic kidney disease staged?
Two measures are used:
- Albumin:creatinine ratio ACR - A1/2/3
- GFR - G1/2/3a/3b/4/5
What is ACR?
ACR is urine albumin to creatinine ratio.
Creatinine is assumed to be consistent (reminder: serum creatinine is used for GFR)
Used for convenience sake to check for proteinuria, in lieu of 24 hour urine collection.
Measured: by spot specimen urine sampling, to find creatinine and albumin concentrations, then dividing albumin (mg) by creatinine (g) - classification; A1 to A3
Increased ratio means there is more kidney damage therefore allowing more protein through the glomeruli.
What is Tamm-Horsfall glycoprotein (THP)?
Tamm-Horsfall glycoprotein AKA uromodulin a glycoprotein secreted by renal tubules.
It is the most abundant protein in urine, and can be up to 150mg per day.
It defines mild proteinuria (- note that more severe proteinuria is microalbuminaemia)
What is proteinuria?
Proteinuria is defined as >150mg/day, most of the low molecular weight proteins are reabsorbed.
This 150mg is made up of 30mg or less albumin, and then Tamms Horsfall protein, b2 microglobulin, immunoglobulin light chains and others.
Dipsticks don’t detect smaller proteins since the result would always be positive, so they detect albumin.
Early renal disease = >150mg/day low molecular weight proteins.
This indicates increased glomerular permeability.
Microalbuminaemia = 30-300mg/day
This is proteinuria but specifically with increased albumin, which is a large protein, and shouldn’t be able to cross the glomerulus unless it is damaged, indicating glomerular or tubular disease.
Severe albuminuria = >300mg/day this is the point at which dipsticks become positive
When do primary care refer a patient with decreased GFR?
GFR <60 is the threshold for referral but not unless it is progressive or very low, also any other indications of serious kidney dysfunction/disease (proteinuria, haematuria, HTN, vasculitis, other)
GFR:
30-59 and progressive = routine referral if the renal impairment is progressive (>25% in a year or >15ml/min in a year)
30-59 but no progression = consider referral if there is:
- haematuria
- proteinuria
- unexplained anaemia
- abnormal potassium/calcium/phosphate
15-29 = urgent referral
<15 = immediate referral
Other indications for referral:
Proteinuria - urgent If nephrotic syndrome (oedema: high proteinuria and low serum albumin)
Haematuria - visible or invisible with proteinuria
HTN - malignant or uncontrolled
Systemic illness - vasculitis, myeloma, sarcoidosis (these most often involve the kidney)
Renal outflow obstruction
When looking at a kidney on ultrasound, what are the shapes and sizes you might see that constitutes evidence of chronic kidney disease?
Reminder: a normal kidney is 11cm between its poles
Polycystic kidney - massive, amorphous (18+cm) with fluid filled spaces within it
Atrophic - small, (7.5cm) sclerosed, shrunken
Hypertrophic - enlarged due to compensation for other kidney
What are possible histopathological findings from biopsy that support a diagnosis of CKD?
Eosinophilic areas within the glomerulus (- nodular glomerulosclerosis in DM)
Fibrocellular crescent around the outside of the glomerulus (- crescentic glomerulonephritis)
Eosinophilic cast within the tubule (- cast nephropathy or myeloma kidney)
Lots of cells between the glomeruli (- acute interstitial nephritis due to white cell invasion)
What is a normal eGFR for a healthy adult age 25?
100-120
What are the five stages of CKD, as defined by eGFR?
Stage 1 - GFR >90: kidney damage with normal GFR
Stage 2 - GFR 60-89: kidney damage with mild decrease in GFR
-NOW WE START TO REFER-
Stage 3 A/B - GFR 30-59: moderate decrease in GFR
Stage 4 - GFR 15-29: Severe decrease in GFR
Stage 5 - GFR <15: Established kidney failure
Why is stage 3 CKD split in to stage 3A and stage 3B But the other stages aren’t split?
Most CKD patients lie within stage 3, therefore it is split to better indicate the kidney function.
Why is it left as a single stage then?
Because the confidence interval for the eGFR calculation is 95% between eGFR of 31-59, so a patient’s true GFR is anywhere within this range.
Why is there a correction in eGFR for African Caribbean patients?
There is a presumed increased muscle mass, which means that creatinine is expected to be higher with perfectly functioning kidneys.
I.e. the molecule used to make estimations is assumed to be at higher concentration but without any kidney dysfunction
So an Afro Caribbean patient can have a higher creatinine than his Caucasian counterpart but they will both have the same kidneys
Why do we use the patient’s weight in the calculation of their eGFR?
Weight is a reflection of muscle mass, which is a reflection of creatinine production.
Someone with a low weight and a high creatinine is more worrying than someone with high weight and high creatinine.
You should eyeball the patient to decide this.
When a patient presents with signs of fluid overload, which two bedside tests should be done to exclude renal causes?
Bedside tests:
- Urinalysis - for proteins and haematuria, since this indicates glomerular damage
- Blood pressure readings - one of the first signs of renal dysfunction
If urinalysis of a patient with fluid overload symptoms shows protein 3+, what is the likely issue?
Protein 3+ indicates glomerular dysfunction, proteinuria only occurs in damage to the filtration barrier.
Without haematuria we put bladder cancer to the back of the pile of differentials.
Which conditions can cause an decrease in specific gravity of urine?
Decrease in SG = less solute, more water
So:
Excessive hydration
Diabetes insipidus
Acute tubular necrosis
Which conditions can cause an increase in specific gravity of urine?
Increase in SG = more solute, less water
So: Dehydration SIADH CHF Cirrhosis Glycosuria Proteinuria Recent IV contrast
What is the normal pH range for urine? Can we use this to decide if the patient is acidotic or alkalotic?
Urine pH = 4.5 - 8.0
No, we cannot establish their serum acidity or alkalinity because urine pH varies widely depending on diet
What conditions cause a decrease in urine pH?
Higher acidity results from:
Acidaemia, which can be due to diet, or any condition causing acidosis; sepsis, DKA, HHS, type 2 respiratory failure etc
What conditions cause a rise in urine pH?
Increase in alkalinity:
Anything that causes alkalosis - metabolic alkalosis from ingestion, prolonged vomiting, hypovolaemia, diuretic use (loss of H+), Hypokalemia.
Distal renal tubular necrosis
UTI - secondary to urease producing organisms (klebsiella, proteus)
