Blood ketone and glucose meters: what to buy

Ketones are worth measuring for one of two reasons, and both of them are about a decision rather than curiosity.

What a ketone reading is for

If you take insulin, the reading is a safety check. Illness, infection or a missed dose can push blood glucose up, and the symptoms of a high reading (thirst, needing to pee, nausea, stomach pain, tiredness) look the same as the start of diabetic ketoacidosis. Ketones separate the two. The NHS asks people with diabetes to test for ketones when their blood glucose is high and when they are unwell, and publishes what to do at each level [1]. Symptoms of DKA usually build over about 24 hours, sometimes faster, so the test has to happen at home rather than at the next appointment.

If you do not take insulin, the reading answers a different question: whether the diet is doing what you think. BHB is the ketone blood meters measure and the one the research reports in mmol/L, so a blood reading is the only home number that can be set next to a trial result. Nutritional ketosis is commonly quoted as 0.5 to 3.0 mmol/L. There is little to do differently at 1.1 than at 2.4, but a reading that has fallen to 0.2 after months at 1.5 tells you something in the routine has changed.

Why the number has to be close

Ketone results are thresholds, not scores. The NHS lines sit at 0.6, 1.6 and 3.0 mmol/L, and each one maps to a different action: carry on as normal, retest in two hours, ring the diabetes team, call 999 [1]. A true reading of 3.0 measured 20% out lands at 2.4 or at 3.6, and only one of those means calling an ambulance. Accuracy matters at those lines and hardly at all in the middle of the range.

What you are buying

The meter is the cheap half of the purchase. A glucose meter kit costs £13 to £39 in the UK; the strips that feed it cost 17p to 41p each, and a blood ketone strip costs £1.50 to £2.29. Whatever meter you buy fixes what you pay for the next few years, because strips only fit the model they were made for.

If you have diabetes, check what you already get before buying anything. The NHS supplies a meter, lancets and strips for type 1, with the expectation of at least four glucose checks a day [2], and ketone kit when your team wants you testing [1]. Buying is for the gap: ketone strips your team has not issued, a second meter to keep in a bag, or ketosis tracking without diabetes.

Prices below come from the Diabetes UK shop on 21 October 2026, at the VAT-relief price. Relief applies to people buying for their own diabetes. Without it, add 20%: the 4SURE Smart kit is £18.33 with relief and £21.99 without.

Glucose meters, priced per test

Pack prices at VAT relief, then cost per strip:

• Contour Plus Blue kit £24.99, 50 strips £8.74 (17p a test)
• GlucoNavii kit £13.33, 50 strips £12.91 (26p)
• 4SURE Smart kit £16.66, 50 strips £14.16 (28p)
• TRUE METRIX, 50 strips £14.63 (29p), 100 strips £20.83 (21p)
• FreeStyle Lite, 50 strips £17.71 (35p)
• Contour Next, 50 strips £20.41 (41p)

The cheapest meter is not the cheapest to run. The GlucoNavii kit costs less than half the Contour Plus Blue kit, and its strips cost 53% more per test. At four tests a day, that 9p gap is £131 a year.

Meters that read ketones as well

• 4SURE Smart Duo kit, £18.33, with 10 glucose strips and one ketone strip. 4SURE ketone strips, 10 for £17.99 (£1.80 a test).
• GlucoMen Areo GK set, £30.68, with 10 glucose strips. Areo ketone sensors, 10 for £16.95 (£1.70).
• FORA 6 Duo kit, £32.38, with 50 glucose strips and 10 ketone strips. Refills: ketone strips 10 for £14.99 (£1.50), glucose strips 50 for £14.41 (29p).
• FreeStyle Optium glucose strips, 50 for £18.33 (37p), and Optium β-ketone strips, 10 for £22.91 (£2.29). The shop lists both as compatible with the FreeStyle Libre reader as well as the Optium meters, so someone already on Libre can test ketones without carrying a second device.

Per test, a ketone reading costs four to thirteen times a glucose reading, depending on which pairing you land on.

Why blood rather than urine

Urine strips read acetoacetate. Meters read β-hydroxybutyrate, the ketone that dominates in blood, and the two do not move together: β-hydroxybutyrate rises first and is converted back to acetoacetate as an episode resolves, so a urine strip can read low at the start and still read high at the end, after blood has come down [4].

The clinical case comes from A&E triage. Arora and colleagues tested 516 hyperglycaemic patients, 54 of them in DKA. A blood β-hydroxybutyrate cut-off of 1.5 mmol/L and a urine dipstick caught the same share of cases, 98.1%. Specificity was 78.6% for blood and 35.1% for urine, so the dipstick flagged about three patients for every true case [5].

The urine equivalent is coarser: on a dipstick, over 2+ is the 999 line [1].

Where the accuracy numbers come from

Glucose meters are held to ISO 15197: at least 95% of results within 0.83 mmol/L of the laboratory value below 5.55 mmol/L, or within 15% at or above it, and at least 99% inside zones A and B of the consensus error grid [6]. Pleus and colleagues put 18 CE-marked systems through it; 14 of the 18 met the 95% criterion [6].

ISO 15197 is written for blood glucose monitoring systems, so nothing comparable covers ketone strips. The accuracy statement on a ketone box is the maker's own testing, and there is no published comparison of ketone strip brands to match the glucose work.

What I would buy

If your clinic supplies your meter, keep it and check the ketone supply separately: ask whether the strips you have been given test blood or urine. NICE prefers capillary blood when DKA is suspected in adults [3], and the same reason holds at home.

If you use a FreeStyle Libre reader, buy Optium ketone strips and nothing else. Ten for £22.91 is the dearest ketone test here, and it still costs less than a second meter you will use twice a year.

If nobody is supplying you, the FORA 6 Duo kit at £32.38 is the cheapest way to get both tests in one device with ten ketone strips in the box. The 4SURE Smart Duo is £14 cheaper up front, then costs 30p more for every ketone test after that.

If you are tracking nutritional ketosis rather than watching for ketoacidosis, do the annual sum before you buy the expensive option. Ketone strips at £1.50 a test, twice a day, come to £1,095 a year, which is why most people following a ketogenic diet keep a blood meter for the occasional check and use urine strips for the daily trend.

Two ways to waste money

Strips are not interchangeable between meters, even within one brand: 4SURE ketone strips fit the Smart Duo, Areo ketone sensors fit the Areo GK, and Optium strips fit the Optium, the Optium Neo and the Libre reader. Buy the wrong box and you have spent £18 on ten strips you cannot use. Ketone strips come ten to a pack and most people use them rarely, so buy them against the expiry date rather than in bulk.

At one ketone test a week, the gap between the cheapest strip here and the dearest is £41 a year. At one a day it is £288, which is more than the meter that reads it.