Nursing care
Glucose meter reads HI or LO: assess, confirm and treat safely
Written and reviewed by Dana Whitfield, RN, MSN · 4 min read · Updated October 2026
Short answer
A meter showing HI or LO means the glucose is outside the range the device can measure, not a specific value. The nurse assesses the client, checks for testing errors and follows protocol to send a laboratory sample and notify the provider. A client with symptoms of low blood glucose is treated under the hypoglycaemia protocol without waiting for the lab result.
What HI and LO actually mean
Point-of-care meters have a measuring range set by the manufacturer. A hospital procedure for one widely used meter notes that the device does not flag critical results at all; it only displays HI or LO when glucose is above or below its measuring range. The display therefore says the result is extreme or unmeasurable, but it does not tell the nurse the actual number.
Meter readings can also be distorted. FDA information lists factors such as abnormal haematocrit, severe dehydration and some interfering substances, and poor perfusion or a contaminated fingertip can mislead the result. An extreme or unexpected reading that does not fit the client's condition is a signal to confirm rather than to act on the number alone.
The first action: assess the client
Go to the client and assess level of consciousness, behaviour, sweating, tremor, heart rate and breathing. Signs of low glucose include shakiness, sweating, confusion and drowsiness. Very high glucose may come with thirst, frequent urination, dehydration and, in ketoacidosis, deep rapid breathing or abdominal pain. The assessment decides how urgent the next step is.
Check the test itself: the fingertip should be clean and dry, the strip in date and the meter's quality control current. Repeat the test if protocol allows. Local procedures commonly direct the nurse to consult the provider and send a venous or arterial specimen to the laboratory when a result is critical or does not match the clinical picture.
When to treat before the laboratory result returns
A LO reading in a client with symptoms of hypoglycaemia, or in one who is drowsy or unresponsive, is treated straight away under the hypoglycaemia protocol, with the confirmatory sample drawn without delaying treatment. Low blood glucose can quickly impair brain function, so waiting for a laboratory value creates avoidable risk.
A HI reading is different. The nurse notifies the provider promptly, sends the laboratory sample and assesses for hyperglycaemic emergencies, but does not guess an insulin dose for an unmeasured value. Insulin decisions follow the provider's order and protocol, often once the actual glucose and other results such as ketones and electrolytes are known.
Distractors and an original study scenario
Imagine a hypothetical client whose meter reads LO before lunch. They are pale, sweaty and slow to answer. The options are to repeat the test with a new strip, send a laboratory glucose and wait, document the reading and inform the next shift, or treat hypoglycaemia per protocol while arranging confirmation. Treating now is strongest because the client is symptomatic.
Now change the stem: the client is alert, warm and chatting, and the meter reads LO after a fingerstick taken just after handling food. Here repeating the test properly and confirming with the laboratory is reasonable, because the reading does not match the client. Assistive personnel may perform checks where policy allows, but must report out-of-range results immediately.
Documenting and following up an out-of-range reading
Record the meter display exactly as shown, such as HI or LO, rather than inventing a number, along with the time, the client assessment, any treatment and the time the laboratory specimen was sent. Note the provider notification and response. Clear records stop the next nurse from treating the same reading twice or missing that a result is pending.
Recheck glucose after treatment as the protocol directs and compare the meter with the laboratory result when it returns. A large mismatch between the two can point to a technique problem or a meter fault, so report it according to point-of-care testing policy. Repeated extreme readings are a reason to review the client care plan with the provider.
Sources and further reading
Island Health: Performing a patient blood glucose test (Accu-Chek Performa). HI and LO displays mean results outside the measuring range; critical or non-correlating results prompt provider consultation, repeat testing or a laboratory sample.
FDA: Blood glucose monitoring devices. Interfering substances, haematocrit and dehydration effects, and comparing meter readings with laboratory testing.
MedlinePlus: Low blood sugar self-care. Symptoms of hypoglycaemia and the need for prompt treatment.
The next step on this is the same as on everything else here: answer questions and read the rationales. Our dosage calculation and lab values practice questions are the closest set to what this page covers.
Common questions
Does HI on a glucose meter give a value the nurse can use for insulin?
No. HI only means the glucose is above the meter's range. Notify the provider, send a laboratory sample and follow orders rather than estimating an insulin dose.
Should the nurse wait for the laboratory result before treating a LO reading?
Not if the client has signs of hypoglycaemia. Treat under protocol immediately and send confirmation without delaying treatment.
What can make a bedside glucose reading inaccurate?
Contaminated or wet fingertips, expired strips, failed quality control, abnormal haematocrit, poor perfusion, severe dehydration and some interfering substances.
More on dosage calculation and lab values