Renal function investigations Flashcards
What is renal clearance?
Theoretical concept which aims to quantify the rate at which a substance is removed from the bloodstream.
How is Glomerular Filtration Rate (GFR) defined?
Volume filtered by glomeruli per unit time.
What is the formula for calculating renal clearance?
Cl = c_urine . UO / c_plasma
What does GFR correlate with?
Global renal function and general loss of kidney function.
Why is GFR important for managing chronic kidney disease (CKD)?
Guides management and predicts the need for renal replacement therapy.
What are the units for GFR?
mL/min
What substance is often used to measure GFR in research?
Inulin
What is the Cockcroft-Gault equation used for?
To estimate GFR based on plasma creatinine, age, weight, and sex.
Fill in the blank: GFR = c_urine . UO / c_plasma for a substance that is completely lost from the plasma to the _______.
urine
What is a major limitation of creatinine clearance for measuring GFR?
Inconvenient for patients and may be inaccurate.
What is the relationship between plasma creatinine levels and GFR?
Reciprocal relationship.
What is an endogenous substance used for GFR measurement?
Creatinine
What method is used for estimating GFR in large populations?
Estimated GFR (eGFR) based on plasma creatinine measurement.
True or False: GFR must be altered by substances that are freely filtered at the glomerulus.
False
What does the term ‘clearance’ refer to in renal physiology?
Volume of plasma completely cleared of a substance per unit time.
What is the significance of measuring GFR?
Provides assessment of global renal function and guides management.
What does it mean if a substance is ‘completely lost’ from the plasma?
Its concentration in the venous blood is zero.
What is the MDRD study known for?
Large study that derived the eGFR equation applicable to patients with renal disease.
What factors are taken into account in the eGFR equation?
- Age
- Sex
- Ethnicity (rarely recorded)
Fill in the blank: GFR loss is correlated with general loss of _______.
function
What is the role of EPO secretion in renal function?
Regulates red blood cell production.
What does the term ‘acid-base balance’ refer to in renal physiology?
The regulation of pH levels in the body.
What is the relationship between GFR and drug dosing?
GFR is used to guide dosing of potentially toxic (renally cleared) drugs.
What does GFR stand for?
Glomerular Filtration Rate
What is the significance of eGFR values greater than 60 mL/min/1.73 m²?
They are not quantified.
What does MDRD stand for?
Modified Diet in Renal Disease
What is the primary limitation of the MDRD equation?
It is only applicable to those with low GFR and is inaccurate at healthy GFR.
What does EPI in eGFR stand for?
CKD Epidemiology Collaboration
Why is the EPI equation considered more reliable than MDRD?
It generates more reliable eGFR at 60–90 mL/min/1.73 m².
In which populations do both MDRD and EPI equations lose applicability?
- Children
- Pregnancy
- Very elderly
What is Chronic Kidney Disease (CKD)?
Progressive and irreversible loss of kidney function caused by irreversible damage to nephrons.
What are some of the adverse outcomes associated with CKD?
- Increased cardiovascular risk
- Progressive renal disease
What is the classification criteria for CKD based on eGFR?
eGFR consistently <60 mL/min/1.73 m².
What can justify a CKD diagnosis even with eGFR >60?
- Persistent proteinuria/microalbuminuria
- Haematuria
- Renal anatomical/genetic abnormality
What characterizes Acute Kidney Injury (AKI)?
Abrupt loss of renal function, commonly with oliguria and increases in plasma urea & creatinine.
According to NICE guidelines, what defines AKI?
Any of the following: * Plasma creatinine increase ≥26 µmol/L within 48 hr
* ≥50% increase in the last 7 days
* UO <0.5 mL/kg/hr for >6 hr in adults
What is the role of AKI e-alerts?
To determine a creatinine baseline and calculate the magnitude of creatinine rise.
What is the function of renal tubular function?
Essential for electrolyte, water, and acid-base homeostasis.
What is the typical pH of urine compared to plasma?
Urine pH <5.5 vs. plasma pH 7.35 - 7.45.
What condition can lead to urine pH >5.5?
Renal Tubular Acidosis (RTA) type I.
What test can confirm suspected RTA type I?
Ammonium chloride loading test.
What does the fractional excretion of phosphate (FEP) measure?
It assesses renal handling of phosphate relative to creatinine.
What does hypernatremia typically reflect?
Water deficit rather than sodium overload.
What urine sodium level indicates appropriate reabsorption?
Urine Na+ <30 mmol/L.
What is a common cause of hypokalemia?
Renal loss, GI loss, or shifts into cells.
What indicates loss of urine concentrating ability?
Accompanied by polyuria.
What can cause diabetes insipidus?
Inability to concentrate urine, leading to Osm urine < Osm plasma.
What is polyuria?
Excessive urination, often associated with high glucose levels overwhelming urine concentration ability
In diabetes insipidus, how does urine osmolality compare to plasma osmolality?
Urine osmolality is less than plasma osmolality
What is the role of renal tubular function?
Essential for electrolyte, water, and acid-base homeostasis
Where does reabsorption of water occur in the kidneys?
In the distal tubules
What does the ability to concentrate urine allow for?
Water homeostasis and fluid balance
How is urine concentrating ability assessed?
By measuring urine osmolality and comparing it to plasma osmolality
What condition may accompany the loss of urine concentrating ability?
Polyuria
What is involved in the water deprivation test?
Withholding fluids over several hours under close monitoring
What is a potential consequence of true diabetes insipidus?
Hypernatraemia
What causes diabetes insipidus?
Failure of action of vasopressin (ADH)
What are the two types of diabetes insipidus?
- Cranial (hypothalamic/pituitary pathology) * Nephrogenic (tubular problem)
What is the normal response of the kidneys to plasma osmolality?
Plasma osmolality remains static while urine osmolality rises
In diabetes insipidus, what happens to urine concentration?
Urine remains dilute despite rising plasma osmolality
What is DDAVP?
Synthetic vasopressin used to treat cranial diabetes insipidus
What is a dipstick urinalysis?
A rapid, simple, convenient, and cheap test for various urine components
What can dipstick tests detect?
- Glucose * Ketones * Protein * Blood * Leukocytes * Nitrites * Bilirubin * Urobilinogen * pH * Specific gravity
What is the primary function of glomeruli in relation to urine protein levels?
Prevent passage of most large plasma proteins
What can renal pathology lead to regarding protein levels?
- Increased glomerular permeability * Decreased tubular protein reabsorption
How can proteinuria be detected?
- Dipstick testing * Lab-based albumin/protein measurement * 24-hour collection * Spot urine using creatinine to adjust for concentration
What does microalbuminuria refer to?
Abnormal level of albumin, usually too low for detection by urine dipstick
What are the thresholds for microalbuminuria in men and women?
- Men: ACR > 3.5 mg/mmol * Women: ACR > 2.5 mg/mmol
Why is microalbuminuria important?
For the prevention of significant diabetic nephropathy
What can cause transient microalbuminuria?
- Post-trauma * Surgery * Pyrexia * Vigorous physical exercise
