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Test Code I2SW Iduronate-2-sulfatase, Whole Blood

Reporting Name

Iduronate-2-sulfatase, B

Useful For

Diagnosis of mucopolysaccharidosis II (MPS II, Hunter syndrome) in whole blood specimens

Method Name

Fluorometric Enzyme Assay

Performing Laboratory

Mayo Medical Laboratories in Rochester

Specimen Type

Whole blood

Necessary Information

Provide a reason for referral with each specimen.

Specimen Required

Collection Container/Tube:

Preferred: Lavender top (EDTA)

Acceptable: Yellow top (ACD)

Specimen Volume: 2 mL

Specimen Minimum Volume

0.5 mL

Specimen Stability Information

Specimen Type Temperature Time
Whole blood Ambient (preferred) 7 days
  Refrigerated  7 days

Reject Due To









Reference Values

≥1.5 nmol/h/mL

Day(s) and Time(s) Performed


CPT Code Information


LOINC Code Information

Test ID Test Order Name Order LOINC Value
I2SW Iduronate-2-sulfatase, B 79462-8


Result ID Test Result Name Result LOINC Value
61902 Iduronate-2-sulfatase, B 79462-8
35211 Reviewed By 18771-6
35212 Interpretation (I2SW) 59462-2


This test cannot reliably determine carrier status for mucopolysaccharidosis II.

Specimen Retention Time

1 year

Method Description

The whole blood specimen is spotted onto filter paper. A 3-mm (one-eighth-inch) disk is punched out of the dried blood spot (DBS) into a microcentrifuge tube and 100 mcL of 0.2%, heat/pH inactivated bovine serum albumin is added as a preincubation extraction which takes place on an orbital shaker for 30 minutes at 37° C. Ten mcL of the extraction liquid is combined with 20 mcL of 1.25 mM 4-methylumbelliferyl-alpha-Ido-A-2S in acetate buffer as the substrate in a black 96-well plate (30 mcL total volume plus DBS). A blank is prepared using only preincubation extraction liquid, substrate, and filter paper punch containing no blood (30 mcL total volume plus blank punches). All patients, controls, and blanks are set up in duplicate (extraction liquid from each of the microcentrifuge tubes). After the incubation period (24 hours at 37° C), 40 mcL of 0.2 M sodium phosphate/0.1 M citric acid, pH 4.5 and 10 mcL of LEBT solution (lysosomal enzymes purified from bovine testis) are added to the same plate. After a second incubation (24 hours at 37° C), 200 mcL of stop buffer (0.5 M NaHCO[3]/0.5 M Na[2]CO[3] plus 0.025% Triton X-100, pH 10.7) is added to all wells (patients, quality control, blanks, calibrators). Calibrators are prepared and analyzed on every plate to calculate enzyme activity results based on fluorescence units in patient wells versus calibrators. The calibration is derived from 4-methylumbelliferone that is serially diluted manually in the plate, with the highest calibrator being equivalent to an enzyme activity of 3.125 nmol/hour/mL blood. The plate is then ready to be read using the spectrofluorometer. Fluorescence readings for duplicate wells are averaged, and the average fluorescence is used to calculate the enzyme activity result.(Civallero G, Michelin K, de Mari J, et al: Twelve different enzyme assays on dried-blood filter paper samples for detection of patients with selected inherited lysosomal storage diseases. Clin Chim Acta 2006;372:98-102)

Test Classification

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

Analytic Time

8 days


Specimens with results below 1.5 nmol/h/mL in properly submitted specimens are consistent with iduronate-2-sulfatase deficiency (mucopolysaccharidosis II: MPS II). If clinically indicated, consider further confirmation by molecular genetic analysis of the IDS gene. Please note that this enzyme's activity can also be reduced in multiple sulfatase deficiency.(1) If clinically indicated, consider biochemical genetic testing of other sulfatases or molecular genetic testing of the SUMF1 gene to exclude MSD.


Normal results (≥1.5 nmol/hour/mL) are not consistent with iduronate-2-sulfatase deficiency.

Clinical Information

The mucopolysaccharidoses are a group of disorders caused by the deficiency of any of the enzymes involved in the stepwise degradation of dermatan sulfate, heparan sulfate, keratan sulfate, or chondroitin sulfate, also known as glycosaminoglycans(GAGs). Accumulation of GAGs (previously called mucopolysaccharides) in the lysosomes interferes with normal functioning of cells, tissues, and organs. Mucopolysaccharidosis II (MPS II, Hunter syndrome) is an X-linked lysosomal storage disorder caused by the deficiency of iduronate sulfatase (IDS) enzyme and gives rise to the physical manifestations of the disease.


Clinical features and severity of symptoms are widely variable ranging from severe infantile onset disease to an attenuated form, which generally has a later onset with a milder clinical presentation. Symptoms may include coarse facies, short stature, enlarged liver and spleen, hoarse voice, stiff joints, cardiac disease, and profound neurologic involvement leading to developmental delays and regression. As an X-linked disorder, Hunter disease occurs primarily in males with an estimated incidence of 1 in 120,000 male births, although symptomatic carrier females have been reported. Treatment options include hematopoietic stem cell transplantation and enzyme replacement therapy.


A diagnostic workup in an individual with MPS II typically demonstrates elevated levels of urinary glycosaminoglycans and increased amounts of both dermatan and heparan sulfate. Reduced or absent activity of IDS can confirm a diagnosis of MPS II; however, enzymatic testing is not reliable to detect carriers. Molecular genetic testing of the IDS gene allows for detection of the disease-causing mutation in affected patients and subsequent carrier detection in female relatives. Currently, no clear genotype-phenotype correlations have been established.


1. New York Clients-Informed consent is required. Please document on the request form or electronic order that a copy is on file. An Informed Consent for Genetic Testing (T576) is available in Special Instructions.

2. Biochemical Genetics Patient Information (T602) in Special Instructions.