Specimen Collection
PST tubes are preferred for collection within ADHB. Heparin, plain, SST tubes are acceptable.
All the above non-fluoride specimens must be received by the laboratory within an hour of collection.
Fluoride tubes should be used if specimens are expected to take >1 hour to arrive at the lab.
Sample stability:
|
Serum
|
Fluoride
|
Fasting glucose reference ranges (patients fasted for a minimum of 8h).
|
Fasting glucose mmol/L |
|
|---|---|
|
<2.8 |
Hypoglycaemia : If accompanied by symptoms or signs, immediate administration of glucose is indicated |
|
2.8 - 3.4 |
Mild hypoglycaemia
: this occurs in some normal people.
|
|
3.5 - 5.4 |
Normal fasting glucose |
|
5.5 - 6.0 |
Borderline
: Possible increased risk of developing diabetes. OGTT indicated if other risk factors for diabetes are present.
|
|
6.1 - 6.9 |
Impaired fasting glucose or 'prediabetes'
. Increased risk of developing diabetes. OGTT may reveal diabetes.
|
|
7.0 or greater |
Diabetic . Indicates diabetes if present on repeat testing. |
Random non-fasting glucose Point of Care Testing (POCT) ranges:
| Age | Capillary whole blood Glucose (mmol/L) |
| 0-29 days | 2.6 - 8.0 |
| 30d - 14yr | 4 - 7 |
| 15yr and above | 4 - 11 |
Pregnancy: see "Gestational Diabetes"
Conversion Factors
: mg/100 mL x 0.0555 = mmol/L
mmol/L x 18 = mg/100mL
Uncertainty of measurement: 5%
** For Whole Blood Uncertainty of measurement refer to the Blood Gases page
Urgent samples: within 1 hour.
Inform the laboratory that the sample is urgent.
Principle: Colorimetric
Reagents: Roche GLU3 kit
Analyser: Cobas c702
Diagnostic Use and Interpretation
After blood collection, blood cells continue to metabolise glucose in the
sample and it is estimated that glucose decreases by 0.2-0.6 mmol/L per hour in
whole blood (1-3), depending on the glucose concentration, temperature,
leukocyte count, etc, and this can also vary between individuals.
Fluoride is an inhibitor of glucose metabolism but it takes about 1 hour to
work. Collection into a fluoride tube can prevent the decrease of glucose in
whole blood beyond the first hour.
Collection in non-fluoride tube is acceptable when samples can arrive at the
lab within 1 hour post-collection because the separation of plasma/serum from
the blood cells by centrifugation in the lab can stop the glucose metabolism.
Therefore, PST tubes are the preferred specimen for collection within ADHB as
other biochemistry tests can be done on the same tube.
When interpreting glucose results, individual biological variation should be
taken into account. The within-subject biological variation for glucose is 5%
(4) and with 95% confidence interval, the variation would be +/- 10% within an
individual. For example, a fasting glucose of 6.0 mmol/L means that it can
range from 5.4 - 6.6 mmol/L within that individual.
Furthermore, there are other factors affecting the glucose levels including
acute illness, stress, medications, diet patterns, physical activity, etc (5).
Stated fasting glucose ranges are provided as a guide to interpretation in clinically stable patients, and should not be used for diagnosis if the patient is acutely unwell, as glucose tolerance can be temporarily significantly impaired. Equivocal results, especially near the diagnostic cut-offs, should be followed-up when patient is clinically stable.
For random (untimed) samples, a glucose result >11 mmol/L in a stable well patient is diagnostic of diabetes if symptomatic. However, the result should be confirmed with a followup glucose and also HbA1c if they are asymptomatic.
An elevated glucose does not necessarily establish the diagnosis if the patient is acutely unwell and especially if on drugs which impair glucose tolerance such as steroids. Status may need to be confirmed once clinical status has stabilised after 3-6 months.
For diagnosis of diabetes mellitus, HbA1c has the advantage of less biological variation (1.2% in healthy subjects) (4) and is less affected by acute changes (6, 7).
References
1. Chan AY, Swaminathan R, Cockram CS. Effectiveness of sodium fluoride as a
preservative of glucose in blood. Clin Chem 1989;35:315-317.
2. Sacks DB, Arnold M et al. Guidelines and recommendations for laboratory
analysis in the diagnosis and management of diabetes mellitus. Diabetes Care.
2011;34:e61-99.
3. Carey R, Lunt H et al. Collection tubes containing citrate stabiliser
over-estimate plasma glucose, when compared to other samples undergoing
immediate plasma separation. Clin Biochem. 2016;49:1406-1411.
4. Carlsen S, Petersen PH, et al. Within-subject biological variation of
glucose and HbA(1c) in healthy persons and in type 1 diabetes patients. Clin
Chem Lab Med. 2011;49:1501-1507.
5. Good to Know: Factors Affecting Blood Glucose. Clin Diabetes. 2018;36:202.
6. Bonora E, Tuomilehto J. The pros and cons of diagnosing diabetes with
A1C.Diabetes Care. 2011;34 Suppl 2:S184-190.
7. New Zealand Society for the Study of Diabetes. Executive Summary of position statement. https://www.nzssd.org.nz/HbA1c/2.%20NZSSD%20exec%20summary%20diagnosis%20of%20diabetes%20Sept%202011%20final.pdf (accessed 15/1/20)
Emails to chemicalpathologist@adhb.govt.nz will receive priority attention from the on-call chemical pathologist.
If the query concerns a specific patient please include the NHI number in your email.
If email is not a suitable option, please contact the on-call chemical pathologist via Lablink (Auckland City Hospital ext. 22000 or 09-3078995).
Individual chemical pathologists may be contacted but will not be available at all times.
After-hours : contact Lablink (Auckland City Hospital ext. 22000 or 09-3078995) or hospital operator for on duty staff after hours.
Dr Samarina Musaad (Clinical Lead) : SamarinaM@adhb.govt.nz ext. 22402
Dr Cam Kyle: CampbellK@adhb.govt.nz ext 22052
Dr Weldon Chiu: WeldonC@adhb.govt.nz ext. 23427
Dr Campbell Heron: CHeron@adhb.govt.nz ext. 23427
Dr Sakunthala Jayasinghe: Sakunthala@adhb.govt.nz ext. 23427