What does 98 on a blood sugar level mean?

by RAM SINGH




QUESTION:


By Ram Singh


My blood sugar reading was 98 mg/dL. Yesterday I became unconscious while driving a scooter. Could this have been caused by low blood sugar?




Quick Answer


A glucose reading of 98 mg/dL, or about 5.4 mmol/L, is not low and would not normally cause unconsciousness. If it was measured only after you recovered, it cannot prove what your glucose was during the blackout, but it is unsafe to assume hypoglycemia was the cause. Loss of consciousness while operating a scooter requires urgent medical evaluation for heart-rhythm problems, fainting, seizure, blood-pressure changes, medication effects, dehydration and other causes. Do not drive again until a clinician has investigated the event and cleared you under local driving rules.



Answer by Dr. Albana Greca, MD, MMedSc


Hello Ram,


The original conclusion that your glucose “must have been below 50” was unsupported. Unexplained loss of consciousness can be serious, especially because it occurred while driving and may have caused injury.



What Does 98 mg/dL Mean?


A glucose of 98 mg/dL equals about 5.4 mmol/L. It is within the usual fasting reference range and is not low after eating.


For most people with diabetes, hypoglycemia means glucose below 70 mg/dL. A value below 54 mg/dL is more clinically significant. Severe hypoglycemia is defined by impaired functioning that requires another person’s help, even when no glucose value was captured.


Feeling shaky at 98 can occasionally occur when glucose has been chronically high and falls rapidly, but true unconsciousness at 98 is not expected. See our low blood glucose guide.



Could an Earlier Low Still Be Possible?


Yes, but only as one possibility. If 98 was measured after you woke, ate or drank something, glucose may have been lower during the event. A meter or CGM reading taken at the time, a witness account and response to glucose or glucagon would provide stronger evidence.


Hypoglycemia is more likely with insulin, glipizide, gliclazide, glimepiride or similar medicines—especially after a missed meal, exercise, alcohol, weight loss or reduced kidney function. Metformin and several other modern medicines have a low hypoglycemia risk when used without insulin or a sulfonylurea.



Other Causes of Sudden Unconsciousness



  • Heart-rhythm disturbance: A fast or slow rhythm can suddenly reduce blood flow to the brain.

  • Cardiac or circulatory disease: Structural heart disease, pulmonary embolism or another cardiovascular problem can cause syncope.

  • Vasovagal fainting: Often preceded by warmth, nausea, sweating, dimmed vision or lightheadedness.

  • Low blood pressure: Dehydration, blood-pressure medicine or position changes may contribute.

  • Seizure: More likely with prolonged confusion, tongue biting, loss of bladder control or witnessed jerking.

  • Neurological emergency: New weakness, facial drooping, speech difficulty or severe headache requires emergency care.

  • Medication, alcohol, anemia, infection or another metabolic disturbance.


Diabetes does not make every blackout a glucose event. Anyone with syncope should receive a medical history, examination, blood-pressure and heart-rate assessment and a resting ECG.



You Need Urgent Assessment


Because this happened yesterday while driving, arrange urgent same-day medical evaluation even if you now feel normal. Bring every medicine, your glucose meter and any reading recorded before or after the event.



  • A detailed account of what happened before, during and after the blackout

  • Blood pressure lying and standing, pulse and cardiovascular examination

  • A 12-lead ECG and, when indicated, heart monitoring

  • Glucose, electrolytes, kidney function, blood count and other targeted tests

  • Neurological assessment and evaluation for injury from the scooter incident



Call emergency services now for another blackout, chest pain, palpitations, breathing difficulty, seizure, severe headache, one-sided weakness, speech trouble, persistent confusion, repeated vomiting, or inability to wake normally. Also seek emergency assessment after a significant head impact.




Do Not Drive Until Cleared


Stop driving cars, scooters and motorcycles until the cause has been assessed and a clinician says it is safe to resume. Driving restrictions after an unexplained blackout vary by country.


Carrying candy is not enough to make driving safe after unexplained loss of consciousness. Fast-acting glucose helps only when hypoglycemia is recognized and the person remains able to treat it.


If you use insulin or a sulfonylurea, discuss a written driving plan: check glucose before driving, never begin a journey with hypoglycemia, carry fast carbohydrate, stop immediately when symptoms occur and wait until glucose and thinking have fully recovered.



If Hypoglycemia Is Confirmed


A severe low should trigger review of medicine dose, meal timing, kidney function, alcohol, exercise and hypoglycemia awareness. People at risk should have ready-to-use glucagon, and family members should know how to use it.


Do not reduce or stop medicine independently. Recurrent or unexplained lows may justify continuous glucose monitoring. See what to do when glucose is too high or too low.



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This educational answer does not replace urgent evaluation of unexplained loss of consciousness.


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