1st-order laboratory parameters-obligatory laboratory tests.
- Blood glucose measurement (glucose during the complaint attack; glucose daily profile).
- Fasting test (72 hours) with measurement of glucose and insulin:
- Inpatient admission and placement of stable venous access.
- Food abstinence for 72 hours, drinking water is allowed; on the day of the fasting test, the patient must also be fasting
- At regular intervals (every two hours) determination of glucose (blood sugar); if the serum glucose level falls below 60 mg/dl (3.3 mmol/l), the control interval should be shortened to hourly measurements
- Discontinuation of the test if:
- If the serum glucose level falls below 50 mg/dl (2.75 mmol/l) or symptoms of hypoglycemia occur
- After 72 hours, if hypoglycemia does not occur.
- In maximal hypoglycemia, blood is drawn for determination of insulin and C-peptide (part of proinsulin):
- Values for insulin and C-peptide elevated above the reference range → endogenous insulin overproduction.
- If glucose serum level rises above 25 mg/dl (1.4 mmol/l) after infusion of 1 mg glucagon → endogenous insulin overproduction (because glycogen reserves are greater in this case); next step is a localization diagnosis regarding an insulinoma (tumor consisting of endocrine cells (islets of Langerhans) of the pancreas (pancreas), in which insulin is produced in increased amounts; frequency: rare; usually benign tumor)
- Result negative in terms of insulin overproduction → search for other causes of hypoglycemia.
In healthy individuals with regular food intake, serum glucose levels are maintained within narrow limits (3.9-6.1 mmol/l mmol/l).Even after 24-72 hours of fasting, serum glucose levels are maintained above 3 mmol/l thanks to counter-regulatory hormones (glucagon, epinephrine) and gluconeogenesis (new sugar formation) from glucoplastic amino acids.
2nd-order laboratory parameters – depending on the results of the medical history, physical examination, and obligatory laboratory parameters – for differential diagnostic clarification.
- Small blood count
- Inflammatory parameters – CRP (C-reactive protein) or ESR (erythrocyte sedimentation rate).
- Liver parameters – alanine aminotransferase (ALT, GPT), aspartate aminotransferase (AST, GOT), glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT, GGT).
- Renal parameters – urea, creatinine, cystatin C or creatinine clearance, as appropriate.
- Alcohol level or, if necessary, CDT (Carbohydrate Deficient Transferrin) – diagnosis and monitoring of alcohol consumption; an increase in CDT, with a daily alcohol consumption of more than about 60-80 g over about two weeks is expected.
- Serum insulin and C-peptide – if insulinoma is suspected, DD of hypoglycemia (hypoglycaemia factitia),
- Cortisol and ACTH (in the morning at 8.00 am), ACTH load test if necessary – if Addison’s disease (primary adrenal insufficiency) is suspected.
- Thyroid parameters* – TSH, FT4, FT3.
- Gonadotropins* – LH, FSH
- ACTH* , cortisol daily profile* (08.00, 12.00, 16.00 h).
- STH* (somatotropic hormone; somatropin).
- Prolactin*
- Estradiol* (in females)
- Testosterone* (in men)
- Fructose in the blood – if fructose intolerance, galactose intolerance is suspected.
* If anterior pituitary insufficiency (HVL insufficiency/ hypofunction of the pituitary gland) is suspected.
