72 hour Fast Protocol

Transcription

1 Page 1 of 5 Principle This procedure provides instruction on how to conduct a prolonged fast. During the fast, a careful record must be kept of exactly what was done, what blood samples were taken and what was to be measured in each blood sample and what symptoms occurred during the fast. Blood samples, 72 hour fast documentation forms and laboratory requisitions must be labelled with the exact date and time of collection to allow for interpretation of results. The "gold standard" test in the evaluation of hypoglycemia is the 72-hour supervised fast. The purpose of the fast is twofold. The first is to diagnose hypoglycemia as the cause of the patient's symptoms. The second is an attempt to determine the etiology of the hypoglycemia. Due to the risk of hypoglycemia, patients should be admitted to the hospital to undergo the fast in a monitored setting. During the fast, patients are allowed no food but can consume non-caloric caffeine-free beverages for up to 72 hours. Simultaneous insulin, c-peptide and glucose samples are obtained at the beginning of the fast and every 4-6 hours thereafter. Once the plasma glucose falls to <3.3 mmol/l, specimens should be taken every 1-2 hours under close supervision. Patients should continue activity when they are awake. The fast continues until the plasma glucose falls below 2.5 mmol/l and symptoms of neuroglucopenia develop, at which time, insulin, glucose, C-peptide, sulfonylurea/meglitinide, proinsulin and beta-hydroxybutyrate levels are obtained and the fast is terminated. Additional samples for insulin antibodies, antiinsulin receptor antibodies, IGF-1/IGF-2 and plasma cortisol, glucagon or growth hormone can also be obtained at this time if a non-islet cell tumor, autoimmune etiology, or hormone deficiency is suspected. The diagnosis of insulinoma is likely if the patient, at the conclusion of the fast, has neuroglycopenic symptoms, a fall in plasma glucose to <2.5 mmol/l, inappropriately elevated beta-cell polypeptides (insulin, proinsulin and C-peptide levels; see below table), beta-hydroxybutyrate level <2.7 mmol/l, and undetectable sulfonylurea/meglitinide levels. Limitations of the prolonged fast: Normal subjects, especially young women, can occasionally have plasma glucose levels of <2.2 mmol/l Rare insulinomas suppress their release of insulin in response to hypoglycemia Insulin levels can sometimes be artificially elevated in the presence of anti-insulin antibodies

2 Page 2 of 5 Scope & Related Documents Successful administration of this protocol requires hospital admission for the performance of this fast as an in-patient; therefore this procedure is restricted to the Sunnybrook campus. The elective admission must be booked in advance with the nonteaching medical team (Orange Team) and the Bed Flow Coordinator. The physician on the Medical Team should call phlebotomy to have a butterfly catheter inserted in vein for multiple blood sampling. An experienced phlebotomist and or nurse coordinator are required along with a dedicated staff person or resident to monitor the protocol from beginning to end. Book the test with laboratory Biochemist prior to the admission of the patient to the hospital. The Biochemist will provide laboratory test guidance and inform senior personnel in specimen management that a 72-hour fast is to begin hour Fast Documentation Form A 72 hour Fast Documentation Form B Materials Tourniquets,gauze,butterfly blood collection kit 2% chlorhexidine in alcohol 1 mg glucagon intravenously injectable Sufficient supply of Gold top tubes (SST), plain green top- (no gel) and grey top vacutainers for duration of fast, crushed ice Patient bradma labels For each period of collection, send copy of most recently recorded Form A and Form B to the laboratory with specimens Test Vacutainer Tube Type Comments Plasma glucose Grey top Send to lab ASAP for testing Insulin Gold top Send to lab ASAP for testing C-peptide* Green top (no gel)-keep on ice Sent to HICL. 15 day TAT-1 ml plasma Proinsulin Gold top Sent to HICL. 90 day TAT-1 ml serum Beta-Hydroxybutyrate Sulfonylurea-indicate type Tolbutamide Chlorpropamide Glyburide (Glibenclamide)** Gold top - Collect at the end of the fast along with the above hormonal assays. Gold top- Collect at the end of the fast along with the above hormonal assays. Sent to HICL. 10 day TAT-1 ml serum Sent to HICL. 15 day TAT -5 ml serum Sent to HICL. 5 day TAT -5 ml serum Sent to HICL. 7 day TAT -2 ml serum

3 Page 3 of 5 * C-peptide must not be collected in a gel barrier tube. **For Glyburide (Glibencalmide or DiabBeta) laboratory must order stabilizing preservative sodium bisulfite or metabisulfite to be added to the serum prior to freezing sample in a -70 C freezer. HICL Hospitals In-Common Laboratory TAT turnaround time for result to become available Safety Follow Body Substance Precautions. See Infection Prevention and Control procedures on the S&W intranet. Procedure 1. Discontinue all nonessential medications. The patient may drink calorie-free and caffeine-free beverages, including plain water. 2. Ensure the patient is active during waking hours. 3. Document time of the last food intake. 4. Record date and time of the onset of the fast 5. Every six hours, until the plasma glucose concentration is below 3.3 mmol/l, collect blood specimens for measurement of plasma glucose, insulin, C-peptide, and proinsulin. Refer to.1 72 hour Fast Documentation Form A and.1 72 hour Fast Documentation Form B (Termination Protocol). 6. NOTE: the decision to end the fast must not be made on the basis of a fingerstick blood glucose value. 7. Label tubes with patient s bradma label. On the bradma label, record date and time of blood collection and tests required. 8. Send blood and copies of most recently recorded 72 hour Fast Documentation Form A and B information to the laboratory after each collection ASAP. 9. Plasma insulin, C-peptide and proinsulin will only be measured in those specimens where the plasma glucose concentration is less than 3.3 mmol/l. Notify the laboratory the time when the patient s plasma glucose concentration is less than 3.3 mmol/l. 10. End the fast*** when any one of the below criteria is met: a. The plasma glucose concentration is less than 2.5 mmol/l, or b. The patient has symptoms or signs of hypoglycaemia, or c. 72 hours have elapsed. 11. At the end of the fast, collect blood for beta-hydroxybutyrate and sulfonylurea along with the other hormonal assays.

4 Page 4 of Inject 1 mg of glucagon intravenously and measure plasma glucose 10, 20, and 30 minutes later. 13. Label tubes with patient s bradma label. On the bradma label, record date and time of blood collection and tests required. 14. Send blood and copies of most recently recorded 72 hour Fast Documentation Form A and B information to the laboratory after each collection ASAP. 15. Feed the patient. ***The decision to end the fast may not be easy. Some patients have slightly low plasma glucose values, but no symptoms or signs of hypoglycemia, while others have the same symptoms during fasting that they have in ordinary life at a time when plasma glucose values are normal. In the latter patients, the symptoms cannot be attributed to hypoglycemia, especially if the hormonal measurements made during fasting are all normal. Young, lean, healthy women may have plasma glucose concentrations in the range of 40 mg/dl (2.2 mmol/l) or even lower after short periods of fasting. Careful questioning and testing for subtle symptoms or signs of hypoglycemia should be conducted repeatedly when the patient's plasma glucose is near or in the hypoglycemic range. To end the fast solely on the basis of low plasma glucose value (except in those patients who have had Whipple's triad documented previously), in the absence of symptoms or signs of hypoglycemia, jeopardizes the possibility of discriminating between normal persons and those with hypoglycemia not mediated by insulin. A low plasma glucose value is a necessary but not sufficient finding for the diagnosis of hypoglycemia. The absence of symptoms or signs (or both) of hypoglycemia and lack of a low plasma glucose concentration during a 72- hour fast precludes the diagnosis of a hypoglycemic disorder. NOTE: The decision to end the fast must not be made on the basis of a fingerstick blood glucose value. 1 Laboratory Processing of Specimens from the 72 hour Fast 1. Glucose requests are processed immediately and ordered in the LIS. Attach the comment, F72, ( 72 hour Fast ) to the test. 2. Insulin, C-peptide and proinsulin tests are not ordered in the LIS and are measured only in those specimens in which the plasma glucose concentration is less than 3.3 mmol/l. Spin down specimens, aliquote and freeze in the -70 C. Identify aliquots with date and time of collection, whether they are heparin or SST and tests to be measured. Dedicate one or two rows in a specimen rack for each collection time. Label rows in the rack accordingly. 1 Mayo Clinical 72 hour fast September 04.

5 Page 5 of 5 3. If there is no collection date and time documented on the specimens sent to the laboratory, document on the tube and aliquots the date and time specimens received in the laboratory. 4. For the sulfonylurea gilbenclamide (glyburide), the laboratory technologist can prepare in advance approximately 20 aliquot tubes containing 10 mg of sodium bisulfite or metabisulfite. Add an aliquot of serum from the vacutainer tube to the tube containing the preservative and freeze as soon as possible. Store and send frozen. If this preservative is not available, indicate on the serum aliquot and requisition that no preservative was added. 5. When resulting all 72-hour fast tests, attach comment code F72 ( 72 hour fast ) and any other relevant comments to the result. Please remember to attach this comment to facilitate interpretation of results by the clinician. 6. To attach a comment to a result: a. At the result screen, select (a) to accept and add a dash [a-]. b. Canned comments are displayed on the bottom of the result screen above the accept/modify prompt line. Each canned comment is assigned a number. c. Select the appropriate canned comment(s) and type the numbered comment next to the dash [a-1, 2,3]. d. When all the comments are attached to the result, press enter to release the result. e. Repeat this process for each of the tests associated with the 72-hour fast protocol. References 1. Hospitals-In-Common Laboratory [homepage on the Internet]. Toronto: Hospitals In-Common laboratory Inc.; c2004 [cited January ]. Available from: 2. Weinstock, RS, Zygmont SV. Pancreatic Islet Function Tests. 2004; [9 screens]. Available at URL: Accessed Feb Mayo Clinic Protocol 72 hour Fast September 04.