Approach to renal disease, Lab assessment, renal biopsy Flashcards
What are the major lab investigations to be done
Evaluate Glomerular function, - GFR, eGFR calculation, Creatinine clearance - Serum Cystatin C levels Evaluate Tubular function, - Concentrating ability - FENa Analyze Urine.
What is the normal GFR for different age groups.
20-30 years: 120 ml/min 30-50 years: 100 ml/min 60 years: 90 70 years: 80 80 years: 70
Formulas for calculating GFR
Cockroft-Gault:
Creatinine clearance
= (140-age) x weight / 0.814 x serumCr
Multiply the result by 0.85 for women, and 1 for men
MDRD formula or CKD-EPI formulas: online calculators accounting for gender, ethnicity, creatinine, BUN, and albumin.
GFR = Creatinine clearance + Urea clearance / 2
Fractional sodium excretion,
what is it used for
what is the calculation
FeNa% = (UrineNa x PlasmaCre) / (PlasmaNa x Urine Cr) x100%
It is the percentage of the sodium filtered by the kidney that is excreted in the urine.
Used to estimate the level of tubular Na-resorption, and thereby distinguish between Pre-Renal AKI and Intra-Renal AKI
Prerenal failure FeNa stays normal at less than 1%
In Acute Tubular Necrosis, FeNa is above 2%
normal values for fractional sodium excretion
Healthy person: FeNa <1%
Hypovolemic person with normal kidney function:
less than 0.1%, and less than 30mMol Na excretion per day.
How to measure renal urine concentrating ability
1) Measure urine specific gravity in the morning before any drinks.
normal values
Osmolarity > 800mOsm
Sp.Grav. > 1022
2) Perform Water deprivation test over 18-24 hours.
Osmolarity should increase above 600 mOsm,
Less than this, or any increase in serum osmlarity (beyond 295-300mOsm normal) means there is impaired concentrating ability.
Stop test immediately if body weight decreases by more than 3% - severe dehydration.
If there is impaired concentration, determine if it is Central or Nephrogenic problem
How to distinguish between central and peripheral Diabetes Insipidus
Administer 5 IU (international units) of Vasopression/ADH
or 40 ug nasal spray Adiuretin (nasal desmopressin/ADH analog)
If urine osmlality increases, then it is central DI, if there is not, then it is nephrogenic.
Test to measure renal acid secreting capacity, and what is it used for
Used to diagnose distal renal tubular acidosis
Acid loading with 0.1 g/Kg of ammonium-chloride
Take urine pH measurement every 2 hours for 6 hours.
Urine pH should drop < 5.3
Plasma HCO3- should drop < 18mM
What are the different colors of urine, what do they indicate
Orange: Rifampicin
Red: Macroscopic hematuria, hemoglobin or myoglobin. Phenytoin, beets.
Brown: Bilirubin, Chloroquine, Nitrofurantoin
Green: Methylene blue, Amitryptiline, Propofol
Darker urine when standing than laying down: Porphyria.
White- Chyluria
What does cloudy urine indicate
Pyuria - pus or bacteria
Chyluria - lymph and fats (chylomicrons)
Hematuria
What can very odorous urine indicate
UTI
Ketonuria
Metabolic disorders - maple syrup urine disease
Normal urine specific gravity range
1001-1046 g/L
pH 5-6.5
What does the urine dipstick test check
pH Hemoglobin Protein Nitrite Leukocytes Glucose Ketones
What tests are used to detect microalbuminuria
Morning urine - with a sensitive dipstick, or calculating albumin creatinine ratio ACR
24 hour collected urine: Albumin excretion rate in mg/24 hours, above 30mg/24 hrs.
Upper end for microalbuminura is 300mg/24 hours
Test must be repeated 3 times. 2 out of 3 positive tests confirms microalbuinuria
False positives: UTIs, Fever, Heart Failure, Strenuous exercise, Uncontrolled Diabetes, and NSAID abuse.
Healthy urinalysis values for:
24 hours albumin excretion
Albumin creatinine ratio
24 hour protein excretion
Protein Creatinine ratio
under 30mg albumin/24 hours
under 3 mg/mMol ACR
under 150 mg/24 total protein excretion
uncer 15 protein creatinine ratio.
