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Three Part Question

[In patients with shock] should [ venous sample be used instead of capillary sample]for [accurate estimation of blood glucose with a glucometer]

Clinical Scenario

You are the senior house officer on duty in the emergency department and a 79 year old male is brought in by his son who states that the patient collapsed at home after having sudden onset central abdominal pain radiating through to the back. He is cold and clammy with a pulse rate of 126/ min and his blood pressure reading is 74/46 mm Hg. You commence active resuscitation and the nurse provides you with a blood glucose reading of 1.2 mmol/l. The test was done with a glucometer on a capillary finger prick sample. You commence IV glucose after sending a venous lab sample. The lab result comes back as 23 mmol/l. You dont understand the reason for the difference between the lab result and the glucometer reading. Meanwhile your consultant has also arrived and she says that she has read somewhere in one of the journals that in cases of impaired peripheral perfusion, the glucometer result on a venous sample is more accurate than the capillary sample for assessment of blood glucose. You decide to do a literature search to find the evidence.

Search Strategy

Medline OVID 1950—June week 3 2010,
The Cochrane Database of Systematic Reviews (CDSR) June 2010.

(capillary sample): ti, ab, kw AND (glucose): ti, ab, kw 0 records

({exp blood glucose OR glucose.mp OR exp glucose} AND {shock.mp OR exp shock OR exp hypotension OR hypotension.mp OR exp Blood Pressure OR low blood pressure.mp} AND {capillary blood.mp OR venous blood.mp OR venous sample.mp OR capillary sample.mp OR capillary.mp OR venous.mp}) limit to humans and English language.

Search Outcome

362 papers of which four papers relevant.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Atkin et al, 1991, USA	25 Hypotensive patients and 39 Normotensive patients in an emergency department	Prospective nonrandomised study	Compare reagent strip glucose values from capillary sample, venous sample and lab result on venous sample in normotensive and hypotensive groups	36 % of capillary values in hypotensive pts within the 20% range of the lab reference value ( 89.7 % in normotensive group) Capillary glucose values significantly different from lab glucose values in hypotensive patients ( p< 0.05) 32% of Hypotensive pts misdiagnosed as hypoglycaemic with capillary sample.	Not randomised Wider glycaemic range in hypotensive pts. Small numbers in study.
Sylvain et al, 1995, USA	38 patients with inadequate tissue perfusion in critical care or emergency department setting	Prospective nonrandomised study	Compare reagent strip glucose values from capillary sample, venous sample and lab result on venous sample.	31.6% of capillary glucose values outside 20% range of lab reference value No statistical difference between venous bedside value and venous lab value (univariate analysis, p = 0.1287). Mean lab venous value significantly different from mean capillary value ( univariate analysis, p< .005).	Not randomised Small numbers in study Definition of shock self defined and not standardised.
Desachy et al, 2008, France	273 blood glucose measurements in 85 patients in ICU, 25 of whom described as being in shock	Prospective diagnostic study	Comparison of reagent strip with whole blood laboratory testing	15% differed from reference value by 20%. Correlation found between discrepancy on testing and low perfusion index (p=0.04). Mean arterial hypotension (p=0.007) and generalised mottling	Small numbers
Lacara et al, 2007, USA	49 critically ill patients in ICU	Prospective diagnostic study	Comparison between reagent strip testing and whole blood testing from arterial or central venous catheter	Authors state no significant difference between point of care and laboratory testing.	Small numbers

Comment(s)

Capillary blood glucose evaluation is routinely performed on patients presenting to the emergency department. The glucometer value on the finger prick sample rather than the laboratory result is used for immediate diagnosis and management of both hypoglycaemia and hyperglycaemia. The evidence appears to suggest that glucometer readings on capillary samples in cases of impaired peripheral perfusion may be incorrect. Although a number of papers show no statistically significant difference, there are a small number in each study where there is a difference which may or may not be clinically significant. Therefore, while in general there is a good correlation of results, there are a small number of outliers and so results from fingerprick testing should be treated with caution.

Clinical Bottom Line

Capillary blood sample results in cases of shock should be interpreted with caution and a glucometer reading on venous sample should be performed.

References

1. Atkin SH. Dasmahapatra A. Jaker MA. et al. Fingerstick glucose determination in shock. Annals of Internal Medicine 1991;114:1020–4.
2. Sylvain HF. Pokorny ME. English SM et al. Accuracy of fingerstick glucose values in shock patients. American Journal of Critical Care. 1995;4:44–8.
3. Desachy A, Vuagnat AC, Ghazali AD, et al. Accuracy of bedside glucometry in critically ill patients: influence of clinical characteristics of perfusion index. Mayo Clin Proc 2008;83:400–5.
4. Lacara T, Domagtoy C, Lickliter D, et al. Comparison of point-of-care and laboratory analysis methods in critically ill patients. Am J Crit Care 2007;16:336–46.