Renal Physiology and Renal Function Tests (2) Flashcards
Measures the rate at which the kidneys can remove or clear a filterable substance from the blood
- Checks how fast the kidney removes a marker from the blood.
Clearance Test
Clearance test that requires a marker – should have specific characteristics;
- removal of a substance from plasma into urine over a fixed period,
- not bound to proteins,
- filtered, neither reabsorbed nor secreted
Markers of the clearance test
- Exogenous substance (administered)
- Endogenous substance (natural in the body)
High clearance test =
efficient excretion
Low clearance test =
inefficient excretion
Normal Value: Creatinine Clearance
in Female
75 - 112 ml/min
Normal Value: Creatinine Clearance in Male
85 - 125 ml/min
expected to have a higher muscle mass and higher body surface area why their normal values are higher
Male
Markers administered/ injected to patients
EXOGENOUS
- Reference method***
- Not routinely done because exogenous
- Soluble, freely filtered, neither secreted, nor reabsorbed
Inulin
127mL/min/1.73m2
Male inulin
118 ml/min/1.73m2
Female inulin
- 125I-iothalamate
- 99m Tc-DTPA
- Iohexol
- 51Cr-EDTA
Radioactive Markers
Creatinine: Ccrea
ENDOGENOUS
waste product of muscle metabolism that is produced enzymatically by creatine phosphokinase from creatine
- 113 Da
- Most widely used marker for GFR
- Produced constantly
- Not bound to proteins
- Not reabsorbed
- Minimally secreted
Creatinine
- Some creatinine is secreted by the tubules
- Chromogens in plasma react in the chemical analysis
- Medications inhibit tubular secretion
- Bacteria break down urinary creatinine
- A diet heavy in meat can raise creatinine
- Not a reliable indicator in patients suffering from musclewasting diseases
- Depends on the completeness of a 24-hour collection
- It must be corrected for Body Surface Area (unless normal)
CREATININE CLEARANCE: DISADVANTAGES
Methods that do not require the collection of timed (24-hour) urine specimens: (blood)
- Estimated glomerular filtration rate eGFR using serum creatinine
- Cystatin C
- Beta2-microglobulin
- Variables - age, sex, weight in kg
- Female - multiply answer by 0.85
- Females are expected to have a lower body mass
Cockcroft & Gault
Six variables: age, sex, serum urea nitrogen, serum creatinine, race, and serum albumin
Simplified MDRD based on four variables: serum creatinine, age, race, and sex
- Serum creatinine obtained with an enzymatic IDMStraceable assay (method to quantify serum creatinine)
- Correspond more closely to the isotope dilution mass spectrophotometry (IDMS)
Modification of Diet in Renal Disease (MDRD)
traceable formula- recommended by the
National Kidney Disease Education Program (NKDEP)
Modification of Diet in Renal Disease
MDRD-IDMS
IDMS
isotope dilution mass
spectrophotometry
MDRD
Modification of Diet in Renal Disease
CKD-EPI
Chronic Kidney Disease Epidemiology Collaboration
Estimates GFR from serum creatinine, age, sex, and race
CKD-EPI
