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Test ID OSG_F Osmotic Gap, Feces

Ordering Guidance

This test is only clinically valid if performed on watery specimens. In the event a formed fecal specimen is submitted, the test will not be performed.

Specimen Required

Patient Preparation: No barium, laxatives, or enemas may be used for 96 hours prior to start of, or during, collection.

Supplies: Stool containers - 24, 48, 72 Hour Kit (T291)

Collection Container/Tube: Stool container

Specimen Volume: 10 g

Collection Instructions: Collect a very liquid fecal specimen.

Useful For

Workup of cases of chronic diarrhea


Differentiating osmotic from non-osmotic causes of chronic diarrhea. 

Profile Information

Test ID Reporting Name Available Separately Always Performed
NA_F Sodium, F No Yes
K_F Potassium, F No Yes
OG_F Osmotic Gap, F No Yes

Method Name

OG_F: Calculation

NA_F, K_F: Indirect Ion-Selective Electrode (ISE) Potentiometry

Reporting Name

Osmotic Gap, F

Specimen Type


Specimen Minimum Volume

5 g

Specimen Stability Information

Specimen Type Temperature Time Special Container
Fecal Frozen (preferred) 14 days
  Refrigerated  7 days
  Ambient  48 hours

Reference Values

An interpretive report will be provided

Performing Laboratory

Mayo Clinic Laboratories in Rochester

Test Classification

This test has been modified from the manufacturer's instructions. Its performance characteristics were determined by Mayo Clinic in a manner consistent with CLIA requirements. This test has not been cleared or approved by the US Food and Drug Administration.

CPT Code Information



LOINC Code Information

Test ID Test Order Name Order LOINC Value
OSG_F Osmotic Gap, F 88697-8


Result ID Test Result Name Result LOINC Value
NA_F Sodium, F 15207-4
K_F Potassium, F 15202-5
OG_F Osmotic Gap, F 73571-2

Day(s) Performed

Monday, Thursday

Report Available

1 to 3 days