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Mayo Clinic Laboratories

Test Code HEXU Iohexol, Timed Collection, Urine

Reporting Name

Iohexol, U

Useful For

Determining glomerular filtration rate in urine specimens

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Specimen Type

Urine

Specimen Required

Supplies: Sarstedt Aliquot Tube, 5 mL (T914)

Container/Tube: Plastic vial

Specimen Volume: 5 mL

Collection Instructions: Collect a timed urine specimen. Timing may be variable and patient dependent.

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type	Temperature	Time
Urine	Refrigerated (preferred)	7 days
	Frozen	35 days
	Ambient	7 days

Reference Values

Not applicable

Day(s) Performed

Monday through Friday

Test Classification

This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information

82542

LOINC Code Information

Test ID	Test Order Name	Order LOINC Value
HEXU	Iohexol, U	93973-6

Result ID	Test Result Name	Result LOINC Value
61712	Iohexol, U	93973-6

Clinical Information

The assessment of glomerular filtration rate (GFR) is an important parameter of kidney function utilized by clinicians in the care of patients with varying kidney diseases, and for clinical research when precise assessment of kidney function is necessary. The GFR is the sum of all the filtration rates of the individual nephrons within the kidney and, as such, reflects the number of functioning nephrons.

Urine concentrations of iohexol can be used for measurement of GFR following a subcutaneous injection of iohexol (plasma disappearance), or during a continuous infusion of iohexol when used in conjunction with plasma iohexol determinations (HEXP / Iohexol, Plasma). The results can be used to determine the clearance of iohexol, which is a measure of GFR.

Interpretation

Low glomerular filtration rate (GFR) values indicate abnormal kidney function, which may be either reversible/transient or irreversible/permanent. GFR tends to decline with age.

Cautions

A theoretical complication to injection of iodinated contrast media (one that has not been observed clinically to date) is the transient suppression of thyroid function in premature and newborn infants. Therefore, a sensitive thyrotropin test is suggested approximately 2 to 3 weeks after an iohexol clearance in that age group.

Clinical Reference

1. Brown SC, O'Reilly PH. Iohexol clearance for the determination of glomerular filtration rate in clinical practice: evidence for a new gold standard. J Urol. 1991;146(3):675-679

2. Gaspari F, Perico N, Ruggenenti P, et al. Plasma clearance of nonradioactive iohexol as a measure of glomerular filtration rate. J Am Soc Nephrol. 1995;6(2):257-263

3. Schwartz GJ, Abraham AG, Furth SL, Warady BA, Munoz A. Optimizing iohexol plasma disappearance curves to measure the glomerular filtration rate in children with chronic kidney disease. Kidney Int. 2010;77(1):65-71

4. Schmit DJ, Carroll LJ, Eckfeldt JH, Seegmiller JC. Verification of separate measurement procedures where analytical determinations influence the clinical interpretation of GFR: Iohexol quantitation by HPLC and LC-MS/MS. Clin Biochem. 2019;67:16-23

5. Seegmiller JC, Burns BE, Schinstock CA, Lieske JC, Larson TS. Discordance between iothalamate and iohexol urinary clearances. Am J Kid Dis. 2016;67(1):49-55

Method Description

Timed urine specimens are obtained after subcutaneous injection of nonradiolabeled iohexol. Iohexol results are acquired via a liquid chromatography tandem mass spectrometry (LC-MS/MS) system. A ThermoFisher LX-2 Cohesive high-performance liquid chromatography system and an ABSciex 5500 MS/MS are used for analysis.(Seegmiller JC, Burns BE, Lieske JC, et al. Discordant glomerular filtration rate determinations between iothalamate and iohexol renal clearances. Poster presented at: Renal Week 2010. 43rd Annual Meeting of the American Society of Nephrology; November 16-21, 2010; Denver, CO)

Report Available

3 to 4 days

Specimen Retention Time

7 days

Reject Due To

All specimens will be evaluated at Mayo Clinic Laboratories for test suitability.

Method Name

Liquid Chromatography Tandem Mass Spectrometry (LC-MS/MS)

Secondary ID

606985

Forms

If not ordering electronically, complete, print, and send a Renal Diagnostics Test Request (T830) with the specimen.

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