Investigations
1st investigations to order
serum glucose
Test
Measure during fasting or acute illness as part of the initial evaluation. During infancy, serum glucose concentration typically falls to <40 mg/gL within 3 to 4 hours after a feed.
Serial measurements are often useful, for instance as capillary blood glucoses, or (ideally) continuous glucose monitoring.
Result
low
serum bicarbonate
Test
Measure during fasting or acute illness.
This test is essential for the characterisation of GSD I.
Result
low
serum lactic acid
Test
Measure fasting or acute illness.
This test is essential for the characterisation of GSD I.
Result
elevated
serum uric acid
Test
Measure during fasting or acute illness.
This test is essential for the characterisation of GSD I.
Result
elevated
serum triglycerides
Test
Measure during fasting or acute illness. Serum may be cloudy or milky with very high triglyceride and moderately elevated cholesterol levels.
This test is essential for the characterisation of GSD I.
Result
elevated
AST and ALT
Test
AST and/or ALT levels may be elevated at diagnosis or at advanced disease stage.
These tests are essential for the characterisation of GSD I.
Result
elevated
Investigations to consider
gene testing
Test
The identification of GSD I genetic variants confirms the diagnosis.[10]
These variants are inherited in an autosomal recessive manner.
Several academic and commercial laboratories offer gene or panel sequencing. GeneTests Opens in new window PreventionGenetics Opens in new window
Result
identification of genetic variants
biochemical profile
Test
Fasting studies and loading studies are mostly considered obsolete. However, after defining the fasting interval from the medical history and supportive tests (clinical chemistry, ultrasound), the biochemical profile of glucose, lactate, ketones and lipids 1 to 2 postprandially can be compared with the profile preprandially.
In a person with suspected GSD I, glucose should decrease and lactate should increase while fasting, without (hyper)ketosis, while triglycerides and cholesterol typically do not undergo major variations.
Result
glucose levels stable, lactic acid levels increase
biochemical markers
Test
Plasma biotinidase and urinary glucose tetrasaccharide (sometimes abbreviated as Hex4) may be elevated.
Result
elevated
liver biopsy
Test
Fasting studies and loading studies are mostly considered obsolete. However, assessment of enzymatic activity in biopsy tissue may be necessary in a small minority of patients who do not have an identifiable gene mutation.
This highly specialised test is offered at a few academic centres.
Result
decreased glucose-6-phosphatase activity
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