Why do you get different blood sugar readings on different fingers?

What to Do When Blood Sugar Readings Vary


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Have you ever double-checked your blood glucose level immediately after an initial reading, only to find completely different numbers? Although it may be impossible for these measurements to be perfect, taking steps to ensure they are as accurate as possible is important for effective diabetes control. Below are a few steps you can take to get the most accurate reading the first time around.

Wash Your Hands

Contamination of the fingers is a common culprit in blood sugar reading variability. That’s because it only takes a little bit of food residue on your hands to impact blood glucose levels. For example, just touching a banana or cutting a piece of fruit can send your numbers sky high. To ensure this doesn’t sway the results, wash both hands thoroughly before testing. And don’t rely on alcohol swabs. Research shows that alcohol doesn’t clean as well as washing hands with soap and tap water.

Check Your Technique

In addition to washing your hands, make sure you follow the user instructions for your meter exactly. For example, too little blood on the test strip can impact its accuracy, and your meter won’t always give you an error message alerting you to the problem. Also, remember to let the blood flow freely when conducting the test. Squeezing your finger can affect the results.

Store It Correctly

Test strips that have expired or have been exposed to extreme heat or cold can provide inaccurate readings. If you use one of these and then move to a new box, you could get very different numbers. Also, make sure you are using the correct test strip. Even if a test strip fits into your meter, it doesn’t necessarily mean it belongs with it. If your strips aren’t made for your meter, you could get inaccurate results.

Consider the Source

Although meters are improving, they are far from perfect. Today’s meters are considered accurate if they are within 20 percent of your actual number. That can account for a lot of variation. To check the accuracy of your meter, bring it with you when you have your blood glucose read in the laboratory. After testing there, check the number against your meter’s finding. If you are concerned about the accuracy of your meter, ask your doctor for recommendations.

Remember, blood glucose can vary somewhat from reading to reading. But the test is still an essential and viable tool for helping you keep your diabetes under control. Take steps to improve its accuracy whenever possible. And if a number seems off, consider taking the test again. Just wash your hands and follow other good testing habits first.

Key Takeaways:

  • Contamination of the fingers is a common culprit in blood sugar reading variability, so wash both hands before testing.

  • Make sure you’re using the correct test strip and that strips haven’t been exposed to extreme heat or cold.

  • To check your meter’s accuracy, bring it along when you have your blood glucose read in the lab. After testing there, check the number against your meter’s finding.

July 9, 2001 — Pricking your finger every day to test your blood for its sugar content is the painful reality of people with diabetes. Recently, relatively pain free devices that take blood from the forearm have become available, but are they accurate?

People with diabetes don’t produce enough of or respond appropriately to a hormone called insulin, which is needed to control the level of sugar in the blood. As a result, many diabetics must routinely check their blood sugar levels to make sure they’re within a healthy range.

Checking blood sugar levels has, until recently, involved taking a painful finger prick. Now manufacturers are answering the need for a less painful way of testing for sugar in the blood by developing devices that require only a very tiny amount of blood from an alternate site on the body, namely the forearm.

New research, however, has called into question the accuracy of blood sugar testing from the forearm. Author of the study, Theodor Koschinsky, MD, PhD, tells WebMD that during rapid blood sugar changes “clinically relevant differences” occurred in blood sugar readings taken from the forearm and the fingertip. He is from the German Diabetes Research Institute and an associate professor at the University of Dusseldorf in Germany.

Koschinsky and his colleague gave men with diabetes a high sugar breakfast followed by a strong insulin treatment in order to make their blood sugar levels go very high then very low. They used both a finger prick device and a forearm device to check their blood sugar levels at several points during the study.

When the amount of sugar in the blood was rising or dropping rapidly, only the finger prick testing accurately caught these rapid changes. It took about 30 minutes for the forearm values to catch up to those reported by the finger prick tests. This research was presented recently in Philadelphia at the annual meeting of the American Diabetes Association.

C. Kurt Alexander, MD, CDE, FACP, has also performed research on the accuracy of forearm vs. finger prick blood sugar testing for Roche Diagnostics, the makers of blood sugar testing devices. He also found that, “a drop of blood out of your forearm is not the same as a drop of blood out of your fingertip.”

Just like most diabetics, I have checked my blood glucose levels twice in a short period of time out of curiosity to find that my glucose meter gives different readings. At first I thought I may have had a faulty meter, but for me and my personal needs a 10% margin of error is not a big deal. Since then I have learned a lot about how different meters work, improvements in the technology used in home testing supplies, government controlled standards for accuracy and the general needs of different kinds of diabetic patients through my work and community engagement.

The short answer regarding meter accuracy is that the technology currently used in home diabetes testing supplies are only capable of testing within a 10-20% +/- margin of error. The FDA mandates minimum accuracy standards for testing supplies in the US, currently following the ISO 15197:2013 standard of 95% of tests must be within +/- 20% for results above 75 mg/dl and +/-15% for results below 75 mg/dl. This standard was issued in 2013, and the majority of manufacturers have redesigned their meters for better accuracy, increased consistency and ease of use since then.

The On Call Express line of products performed much better than FDA standards, and performed better than 90% of meters on the market.

Even though a 15% margin of error might seem large on the surface, Robert Ratner, MD, FACP, the American Diabetes Association’s chief scientific and medical officer says “ accuracy is sufficient for reliable clinical decision making and therapy”. In most cases results taken from an at home blood glucose meter would suggest similar treatment decisions as a result someone would get using laboratory equipment.

How Does a Glucose Meter Work?

To understand why a meter could give differing readings, you first have to understand how they work. The testing strip contains an enzyme that interacts with the glucose in your blood. The mixture generates electrons, which are then converted to an electrical current. The current is transferred from the strip to the meter, which is programmed to read the electrical current as the final numeric value.

A close up view of the design of the On Call Express Test Strip. Notice the reservoir on one end and the contact area on the other.

The variables involved from the manufacture of the enzyme to the actual testing procedure and the test subject are immense. In earlier generations meters had to be coded, or the manufacturer sent a coding chip with each box of strips to alter the formula to match the slight variations in each batch of strips. Today most strips are coded so the end user is unaware that their meter is calibrating itself to each new batch of strips used.

Hospital labs achieve a higher degree of accuracy by controlling variables more closely. Their equipment is kept in an environment with consistent temperature and humidity, and is programmed for those variables. Nurses and technicians are professionally trained to limit variations in testing. The equipment is built with more costly, and more consistent components. Most importantly, blood samples are separated and only the blood plasma is tested (all home testing kits test whole blood). Finally, laboratory machines test a much larger sample for over a minute; at home testing devices are designed to use the smallest sample possible and deliver the fastest results. Even with all those differences laboratory tests generally still have a +/-4% margin of error. Some lab equipment exhibits a +/-5% to +/-8% margin of error.

The most important thing about blood glucose meter accuracy is that you can use the results to make competent and confident decisions regarding your care. If you feel like your meter is inaccurate enough to cause problems with your dosing or treatment, take it with you during your next doctor visit and test simultaneously with the blood sample being drawn for lab testing (be sure to find out if your meter results are converted to Plasma levels or if they’re being reported as whole blood levels). If your reading would have specified a noticeable difference in your treatment, it might be something to worry about. Millions of people use home testing glucose meters every year however, and the FDA receives between 25,000 and 30,000 reports about malfunctions and user errors relating to glucose meters annually. Their standards take real world scenarios and the data associated with those reports into consideration.

Why is Your Diabetes Meter Inaccurate?

Starting with the strip, the chemical process involved relies on an exact amount of blood entering the reservoir in a prescribed amount of time, at a pre-determined temperature and an educated guess assigned to the composition of the blood itself. Not only will one person’s blood differ from another’s in chemical makeup and red blood cell count, contagions on your skin AND the presence of water or alcohol after cleaning can affect the results.

For the strip to have a chance at giving a perfect result you need to use the same amount of blood and fill the strip in the same time frame every time; your blood and the enzyme in the strip needs to be at consistent temperatures. If you think that using two drops of blood from the same lancing site should be more accurate, you’d actually be wrong. The first drop of blood will have more extracellular fluid content than proceeding drops.

Known Variables to Interfere with Test results

  • Meter not calibrated regularly
  • Storage and handling of test strips
  • Not properly cleansing the test site
  • Testing site damp from alcohol prep or water
  • Not enough blood applied to test strip
  • Altitude, temperature, and humidity
  • Change of Test Site
  • Inconsistent Red Blood Cell levels due to dehydration, anemia or polycythemia
  • Interfering substances (Vitamin C, acetaminophen, and uric acid)

Diabetic testing supplies are by design not extremely accurate, but quality control during manufacturing and transport can further affect accuracy. Proper storage by the retailer and finally the patient in a climate controlled environment and keeping an eye on the expiration date will help you limit additional inconsistencies.

4 Tips to Maximize The Accuracy of Your Glucose Meter

Properly Store and Handle Strips– There are two components on your strips that are very sensitive, the chemical that reacts with your blood and the conductor that transmits the reading to your meter.

  • Keep your strips away from sunlight and moisture
  • Testing has shown that cooler temperatures help keep the strips longer
  • Make sure to seal your vial after you take a strip out
  • Avoid getting the oil on your fingers on the chip/ connection point, it can affect the electrical current

Wash your hands– Try to limit contamination by washing your hands, and drying them thoroughly before testing. I would recommend waiting five minutes afterward and then testing to give your hands a chance to dry completely.

Be consistent– Try and use the same amount of blood and get the blood from the same part of your finger. Aim to get as many tests in the same room of your home at the same times of day ( this will control temperature and also make your benchmarks and trends more meaningful). Only use results from the same meter for intense comparison.

Repeat your tests– When an engineer requires a greater degree of accuracy than their equipment is capable, they will often repeat the test a number of times and use the average. This will also allow you to identify outliers or faulty strips.

Some Things to Consider Regarding Glucose Meter Accuracy

For most readings the current accuracy standards are more than acceptable for making treatment decisions – the guidelines require a higher degree of accuracy in the range where a smaller deviation in treatment could lead to serious consequences. Some patients will also be more susceptible to treatment variations due to inaccuracy, particularly children or adults with a lower body weight. If you are concerned with your meter’s accuracy, I would recommend running a test scenario for various levels of tolerance to find out what levels of inaccuracy your treatment can withstand. It’s important to understand the relationship between your test results and your self administered treatment.

Even though manufacturers have been successful at introducing incrementally better products, it will take a holistic re design and breakthrough to make a substantial increase in accuracy. While some meters are slightly more accurate in testing (The Accu-Chek and FreeStyle meters consistently maintain high accuracy scores in testing), we ultimately decided that the On Call Express meter offered the best return on investment, with comparable accuracy testing results of even the highest rated meters – and better results than some of the most popular (and most expensive) alternatives at a substantial savings.

According to the test results we accumulated from manufacturers and 3rd parties prior to selecting the meters we would sell; At the lower threshold where accuracy is most important, only 3 brands had meters that achieved 100% of results within a 10% margin, and those were Accu-Chek, FreeStyle and On Call Express. 71% of the On Call Express results were within 5% (As compared to the One Touch Verio Pro which only had 53% of tests within the 10% margin , and only 21% within the 5% margin). Overall the relatively high accuracy and incredibly good value of the On Call Express won us over.

How to test your blood sugar

When it comes to managing diabetes, it is all about blood sugar. If your blood sugar (or “blood glucose”) levels get too high or too low, it can drastically alter your mood, your well-being, and even your long-term health. There are many ways to monitor blood sugar. Some people use glucose meters with test strips and blood drawn from their fingertips for instant measurements. Others use continuous glucose monitors (CGMs) that are either implanted in their bodies or attached to them. There are also hybrid monitors called “flash glucose meters” (FGMs) that can monitor blood glucose continuously and offer instant readings. Each person is different, so your doctor will review your unique case and recommend the right solution to help you monitor your blood sugar effectively.

When to test blood sugar

Checking your blood glucose as recommended can help you see how your meals, medications and activities affect your blood sugar. The American Diabetes Association (ADA) recommends that you routinely test blood sugar levels to aid in managing your diabetes.1

Routine or daily blood glucose testing

For people using an insulin pump or insulin injections throughout the day, the ADA recommends testing multiple times daily. If you take another kind of medication, test your blood sugar level as often as your healthcare team recommends.

You and your healthcare team will determine when you should check your blood sugar based on your current health, age and level of activity, as well as the time of day and other factors. They may suggest that you test your blood sugar at any of the following times:

  • Before each meal
  • 1 or 2 hours after a meal
  • Before a bedtime snack
  • In the middle of the night
  • Before physical activity, to see if you need a snack
  • During and after physical activity
  • If you think your blood sugar might be too high, too low or falling
  • When you’re sick or under stress

Gaining insights from routine blood glucose testing

Day-to-day blood sugar checks can give you a good idea of how you’re doing at this moment, and they can be reviewed overall to see trends. They can help answer questions such as:

  • Are your medications working as they should?
  • How does the type or amount of food you eat affect your blood sugar?
  • How does activity or stress affect your blood sugar?

Structured blood glucose testing

Structured testing supports your routine or daily testing by giving you deeper, more targeted data to work from. It can help you determine if you’re in a safe range and problem-solve around how the things you do are connected to your blood sugar. You simply perform additional tests over a short period at specific times of day.

Structured blood glucose testing can help you:

  • Discover how to best use your numbers
  • See how certain activities can affect on your blood sugar levels
  • Problem-solve around highs and lows
  • Identify blood sugar patterns
  • Work with your healthcare team decide if any adjustments are needed in your insulin therapy or other areas of your diabetes management

Pattern management: If you find that your A1C result is rising in spite of your best efforts, or if you don’t feel as well as you’d like, talk with your healthcare professional about the Accu-Chek 360° View tool. This simple paper tool helps you track your blood sugar over 3 days, so you and your doctor can quickly identify patterns that can guide adjustments to your treatment plan. As a result, you may be able to feel better and lower your A1C.2

Before-and-after testing: You may also decide to try the Accu-Chek Testing in Pairs tool. This easy-to-use, printable tool helps you see changes in your blood glucose with before-and-after testing. In just 7 days, you can see the effect a specific meal, exercise or other event has on your blood sugar.

To check your blood sugar level, gather your blood glucose meter, a test strip and your lancing device. See how to prepare the meter and test strip, lance your finger and get a reading using the Accu-Chek® Guide Me system by watching the video or following the steps here:

The steps are similar for many meters, and generally look like this:

  1. Wash and dry your hands—using warm water may help the blood flow.3
  2. Turn on the meter and prepare a test strip as outlined in your owner’s booklet. Many Accu-Chek meters turn on automatically when a strip is inserted.
  3. Choose your spot—don’t check from the same finger all the time. Using the side of the fingertip may be less painful than the pads.
  4. Prepare the lancing device according to the user guide provided, then lance your fingertip or other approved site to get a drop of blood.4
  5. Touch and hold the test strip opening to the drop until it has absorbed enough blood to begin the test.
  6. View your test result and take the proper steps if your blood sugar is high or low, based on your healthcare professionals’ recommendations.
  7. Discard the used lancet properly.
  8. Record the results in a logbook, hold them in the meter’s memory or download to an app or computer so you can review and analyze them later.

How to choose a blood glucose meter

There are many blood sugar meters to choose from, so start by thinking about what’s most important to you. Ask yourself a few questions.

  • Are you concerned about accuracy? Make sure you’re using a meter and test strips that provide accurate results. Roche quality control processes ensure consistent accuracy. Find out more about our accuracy commitment.
  • Do you use blood glucose results to dose insulin? The Accu-Chek Guide meter sends results directly to a smartphone app that includes an insulin calculator.5
  • Do you feel like you’re always short on time? A system that syncs your data wirelessly, without manually entering results, can save time with every test. You may also want to consider a blood glucose meter that gives results quickly, makes it easier to handle test strips, doesn’t require coding, or simplifies lancing or dosing.
  • Would you like to reduce the pain of testing? Choose a system with a lancing device specifically designed for comfort, such as the Accu-Chek FastClix lancing device. Precision-guided technology minimizes the lancet’s painful side to side motion and thin-gauge, bevel-cut lancets help ensure smoother entry. Plus, 11 customizable depth settings make it easier to get the right amount of blood the first time.
  • Will you track results in the blood sugar meter, with an app or on a computer? Most blood sugar monitors have built-in memories, and many can beam or transfer data directly to your smartphone or computer. The Accu-Chek product family includes a few of these options, including the mySugr, Accu-Chek Connect, and Glooko™ apps.

What is the normal range for blood sugar?

In general, the American Diabetes Association’s (ADA) recommended blood sugar levels are6:

  • Between 70 and 130 mg/dL before meals
  • Less than 180 mg/dL after meals

Your range is yours alone—based on your health, age, level of activity and other factors. And remember that your target is a range you’d like to stay within, not a single number.

How to use blood glucose testing results

It’s not unusual for your blood glucose results to be out of range now and then. But if you see a pattern of highs or lows outside your target range, you may want to ask yourself:

  • Did I eat at an unusual time, have a larger or smaller portion, or try a new food?
  • Did I have more or less physical activity than usual?
  • Did I forget to take my medication, take it at the wrong time, take too little or too much?
  • Am I taking a new medication?
  • Am I stressed about something?
  • Do I have an infection or an illness?
  • Did I drink alcohol?

Any of these can have an impact on your blood glucose numbers. If you’re making changes to your lifestyle, or if you can’t figure out why you’ve been out of range, talk to your doctor, nurse or diabetes educator.

If you have diabetes, you’re always fighting to keep blood sugar under control. Here’s a way to dial up your efforts: Consider the timing of your workouts after meals.

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Exercising soon after eating has positive effects on blood sugar, says endocrinologist Betul Hatipoglu, MD.

Another plus? Doing this can cut your risk of heart disease.

How soon after meals? This can vary by the person. Here’s how to tell when it’s best for you.

Why it’s better to exercise soon after eating

Glucose levels hit their peak within 90 minutes of a meal, according to a 2017 study published by the journal Frontiers in Endocrinology.

Those with type 2 diabetes are supposed to keep levels at 160 mg/dl within two hours of a meal.

Because exercising reduces blood glucose concentrations, it’s a good idea to start exercising about 30 minutes after the beginning of a meal, researchers concluded.

While this is a solid guideline, it can vary for different people. Read on to find out how to ensure you’re in the safe zone for exercise.

How to tell if it’s safe to exercise

Before you begin your workout, start by measuring your blood sugar, Dr. Hatipoglu says.

When you initiate exercise, your body releases stress hormones, which can briefly raise your blood sugar.

If you have diabetes and your body doesn’t manage blood sugar well, it can increase too much during the first half hour of exercise before it begins to lower.

“If you start exercising with very high blood sugar, it might be dangerous,” she says. “You might need to wait for it to go down a bit before starting your workout.”

She offers four tips for ensuring that your glucose levels are safe for exercise:

  1. If your blood sugar level is between 150 and 180, you are in a healthy range.
  2. If your level is lower than 140 and you take insulin, you may need to eat 15 grams of carbohydrates prior to exercise so the level doesn’t drop too low.
  3. If your level is really high — 300 or more — postpone exercise for a bit and try taking a little insulin before starting.
  4. If you take insulin, check your blood sugar level after exercise to ensure that you have enough fuel. This is particularly important if you are starting a new exercise program.

The American Diabetes Association recommends about 150 minutes of moderate exercise or 75 minutes of rigorous exercise weekly.

Take extra precautions with evening exercise

Exercise does two things for those who have type 2 diabetes, says Dr. Hatipoglu.

First, your muscles need energy to work. To feed them, your body burns sugar as an energy source, lowering the glucose levels in your blood.

Second, when you exercise regularly, it helps your body use insulin more efficiently. This can lower your blood sugar levels for up to 12 hours after you exercise.

Also, keeping blood sugar low on a regular basis can dramatically reduce your risk of heart disease, Dr. Hatipoglu says.

Every person reacts a little differently to exercise, so she recommends tracking your blood sugar levels for four to five hours after post-meal exercise to see what your trend is. This can help you determine if your levels are healthy or drop too much.

This is particularly important if you exercise in the evening.

“Especially after dinner, you need to know what your body will do when you exercise,” she says. “If you go to bed and glucose drops it can create a dangerous clinical situation.”

Exercising after a meal is a good way to reduce blood glucose levels and lower your risk of complications from diabetes, including heart disease.

But, before starting or changing your exercise regimen, talk with your doctor to determine what is best for you.

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