creatinine clearance Flashcards
creatinine
a waste product in the body that comes from the breakdown of muscle tissue and the digestion of protein from food
is GFR the same as EGFR
no, eGFR is an estimate of GFR
note an estimated GFR or 90ml/min/1.73m2 or higher is normal
Estimated glomerular filtration rate is a calculation based on a blood test that measures creatinine levels, age, sex, weight, and height. eGFR is the preferred method for assessing kidney function because it’s simpler than a direct GFR measurement.
describe the following terms;
zero clearance
complete clearance
partial clearance
means that the kidneys are no longer filtering substances and have completely stopped working, and only reabsorption is taking place
this is when substances are completely filtered by the kidneys, neither reabsorbed nor secreted
refers to when the kidney filters substances, but excretes or reabsorbs very little of these substances or nutrients
name some methods for directly measuring GFR
through the inulin clearance method
through radioisotopic means (These methods involve the use of radiolabeled compounds that are filtered by the kidneys, and their clearance from the bloodstream is monitored using specialized imaging techniques. )
with the first method, Inulin is infused into the bloodstream, and urine samples are collected to measure the amount of inulin excreted over time. Inulin clearance is not commonly used in clinical practice due to the need for intravenous infusion and continuous urine collection, which are logistically challenging.
radioisotopic means used when precise estimate is needed, but it exposes patients to radiation and invasive procedures
creatinine cannot be used in isolation to estimate GFR, true or false
true
what are some limitations to using creatinine to estimate renal function
it’s levels can increase or decrease due to numerous factors, so it is not always efficient in the estimation of GFR
SOME OF THESE FACTORS INCLUDE EATING MEAT, CERTAIN DRUGS, MALNUTRITION, PEOPLE WITH LOWER MUSCLE MASS…ETC
what do medications that inhibit tubular secretions of creatinine do to serum creatinine levels
examples of such medications
they decrease creatinine clearance and increase serum creatinine without a change in GFR
Antimicrobial: trimethoprim
Antiarrhythmic: dronedarone
H2 blockers: cimetidine
HIV treatment: dolutegravir and cobicistat and rilpivirine
PARP inhibitors: olaparib and rucaparib
Tyrosine kinase inhibitors: imatinib, bosutinib, and sorafenib.
some effects of a reduced renal function on some drugs
reduced renal excretion of a drug or its metabolites may cause toxicity;
*sensitivity to some drugs is increased even if elimination is unimpaired;
*many side-effects are tolerated poorly by patients with renal impairment;
*some drugs are not effective when renal function is reduced
why is it important to estimate renal function
Screening: Renal function tests can be used to screen for kidney impairment.
Monitoring disease: Renal function tests can help monitor the progression of kidney disease.
Guiding prognosis: An accurate assessment of kidney function can help guide prognosis.
Determining treatment: For patients with cancer, kidney function is important for determining the appropriate dose of chemotherapy drugs and a patient’s eligibility for clinical trials.
Assessing safety of medicines: Renal function tests can help assess the impact of renal impairment on the safety of medicines.
eGFR and CrCl are interchangeable, true or false
false, they are not
what is the recommended method for estimating GFR and calculating drug doses in most patients with renal impairment
the Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) Formula
note that this formular is normalised for a body surface area of 1.73m2
it utilises serum creatinine, age, sex and race as variables. obviously limitations can stem from the parameters it uses
some other methods for measuring or estimating GFR apart from CKD-EPI
Modification of Diet in Renal Disease (MDRD)
Absolute GFR method(here the actual SA of the individual is calculated to measure their actual GFR)
MDRD less accurate than CKD-EPI when eGFR is greater than 60 mL/min/1.73 m2. it also Overestimates GFR in elderly patients. MDRD inaccurate in patients with normal kidney function
how do we estimate creatinine clearance
from a 24 hour consistent urine collection along with a blood sample collected to measure serum creatinine levels
or
using the Cockcroft and Gault Equation
with the 24 hr method, the urine is refrigerated or preservatives are added to it if cannot be transferred immediately to lab
ideally urine should be transferred to lab immediately
urine should be tested within 2hrs
when do we use CrCl
when determining the effects of renal impairment on drug elimination
if explicitly recommended then it is also used in;
elderly patients
treatment with toxic drugs
patients at extremes of muscle mass
cases where there is the use of DOACs
drugs with narrow therapeutic index, which are mainly renally excreted
