SPECIMEN:
24 h urine collection for creatinine, plus a blood for creatinine
(5 mL blood, SST or PST tube)
taken within 24h of the start or finish of the urine collection period.
Accurate timing of the 24h collection is essential.
How to collect an accurate 24h urine
1. Decide on the START TIME of the collection. It is usually most convenient to start in the morning.
2. At the START TIME the patient empties her / his bladder into the toilet (NOT into the bottle). Note the START TIME and date on the bottle(s).
3. All urine passed after this is collected into the bottle(s). If possible refrigerate the collected urine to prevent bacterial growth.
4. At the END TIME (exactly 24h after the START TIME) the patient empties his / her bladder, into the bottle.
5. Deliver the bottle(s) promptly to the laboratory.
Reference Intervals
Calculation:
Creatinine clearance (mL/min) = [urine creatinine (mmol/L) x vol (mL) x 1000] / [serum creatinine (umol/L) x time(min)]
OR
Creatinine clearance (mL/min) = [urine creatinine (mmol/day) x 694] / [serum creatinine (umol/L)]
Reference range:
Units:
mL/min
Corrected creatinine clearance:
If the patient's weight in kg (W) and height in cm (H) are known a corrected clearance can be calculated. This adjusts the result to a standard body surface area of 1.73 sq m.
Body surface area (m
2
): A = W
0.428
x H
0.725
x 0.0072
To apply the correction for body surface area, multiply the uncorrected creatinine clearance by 1.73 / A
Reference:
Dubois D and Dubois EF, Arch Int Med 17: 863, 1916
Turnaround Time: Within 3 hours
Diagnostic Use and Interpretation
Creatinine clearance is an estimate of glomerular filtration rate. It is independent of muscle mass (unlike eGFR).
Creatinine clearance is calculated from the plasma (serum) creatinine and the urine creatinine excretion over a timed period (usually 24h).
The assumption is made that the subject is in a steady-state (i.e. plasma creatinine does not change significantly over several days).
GFR and creatinine clearance decline in the course of the normal aging process.
Contact Information
Emails to
chemicalpathologist@adhb.govt.nz
will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via
Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours
: contact
Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad
(Clinical Lead)
:
SamarinaM@adhb.govt.nz
ext. 22402
Dr Cam Kyle:
CampbellK@adhb.govt.nz
ext 22052
Dr Weldon Chiu:
WeldonC@adhb.govt.nz
ext. 23427
Dr Campbell Heron:
CHeron@adhb.govt.nz
ext. 23427
Dr Sakunthala Jayasinghe:
Sakunthala@adhb.govt.nz
ext. 23427