Effects of different tube types on patient classification using current diabetes decision limits

Plasma Glucose Concentrations in Different Sampling Tubes Measured on Different Glucose Analysers

INTRODUCTION

The German Diabetes Association recommends using sampling tubes with citrate and fluoride additives to diagnose diabetes by oral glucose tolerance test to inhibit glycolysis. The effect of different tubes on measurement results was assessed.

MATERIALS AND METHODS

In a first study, an oral glucose tolerance test was performed on 41 participants without anamnestically known diabetes. Venous blood was sampled in two different tubes with citrate/fluoride additives from different manufacturers and one with only lithium-heparin additive. A second study with 42 participants was performed to verify the initial results with an adapted design, in which a third tube with citrate buffer was used, and glucose measurements were performed on two additional devices of another analyser model. Samples were centrifuged either immediately (<5 min incubation time) or after 20 min or 4 h. All glucose measurements were performed in plasma. Glucose concentrations in lithium-heparin tubes with<5 min incubation time served as baseline concentrations.

RESULTS

In the first study, glucose concentrations in one of the citrate/fluoride tubes were similar to the baseline. In the other citrate/fluoride tube, markedly lower concentrations (approximately - 5 mg/dL (- 0.28 mmol/L)) were measured. This was reproduced in the verification study for the same analyser, but not with the other analyser model. Lithium-heparin tubes centrifuged after 20 and 240 min showed systematically lower glucose concentrations.

CONCLUSIONS

The results confirm that glycolysis can be effectively inhibited in citrate/fluoride-containing sampling tubes. However, glucose measurement results of one analyser showed a relevant negative bias in tubes containing liquid citrate buffer.

Five days serum glucose stability at room-temperature in centrifuged fast-clotting serum tubes and the comparability with glucose in heparin-plasma and plasma containing citrate-stabilizer

Glucose measurement plays a central role in the diagnosis of gestational diabetes mellitus (GDM). Because of earlier reports of overestimation of glucose in the widely used tubes containing granulated glycolysis inhibitor, the study assessed the performance of fast-clotting serum tubes as an alternative sample for the measurement of glucose. Glucose concentration in fast-clotting serum was compared to lithium-heparin plasma placed in an ice-water slurry after sample collection and glucose stability at room-temperature was studied. Blood samples from 30 volunteers were drawn in four different types of tubes (serum separator tubes, fast-clotting serum tubes, lithium-heparin tubes and sodium fluoride, EDTA and a citrate buffer (NaF-EDTA-citrate) tubes, all from Greiner Bio-One). Lithium-heparin tubes were placed in an ice-water slurry until centrifugation in accordance with international recommendations and centrifuged within 10 min. After centrifugation, glucose was measured in all tubes (timepoint T0) and after 24, 48, 72, 96 and 120 h of storage at 20-22 °C. NaF-EDTA-citrate plasma showed significant overestimation of glucose concentration by 4.7% compared to lithium-heparin plasma; fast-clotting serum showed glucose concentrations clinically equivalent to lithium-heparin plasma. In fast-clotting serum tubes, mean bias between glucose concentration after 24, 48, 72, 96 and 120 h and T0 was less than 2.4%. All individual differences compared to T0 were less than 6.5%. The results fulfill the acceptance criteria for sample stability based on biological variation. Fast-clotting serum tubes can be an alternative for the measurement of glucose in diagnosis and management of GDM and diabetes mellitus, especially when prolonged transportation is necessary.

Long term stability of lactate in uncentrifuged sodium fluoride/potassium oxalate blood collection tubes

BACKGROUND

Delayed time from collection to centrifugation may cause erroneously high lactate levels in vitro (from continued blood cell metabolism under anaerobic conditions in the collection tube) if not collected in appropriate collection devices, consequently increasing the risk for inappropriate patient care or harm. We undertook a study to determine the turnaround time for lactate testing in a tertiary care setting and also performed short- and long-term lactate stability studies in blood collected in sodium fluoride/potassium oxalate (NaF/KOx) collection tubes.

METHODS

The hospital lab information system was mined for 6 months to determine patient samples that may have exceeded the time from collection-to-receival in lab of 15-min. Lactate stability was evaluated in unspun NaF/KOx collection tubes at 15 min intervals for to 2 h; and separately at 2, 6, 12, 24, and 48-h post-collection.

RESULTS

A total of 8,929 plasma samples were collected in 6 months, and 1/3 were not received in the lab within 15 min from collection. In NaF/KOx additive, lactate levels had minor increases over 2 h, and incremental increases at an average rate of 0.0035 mmol/L/h over 48 h with maximum increase of 9.8% at 48 h. However, the average change across all time points were within local allowable performance goals (at ≤4 mmol/L ± 0.5 mmol/L; at >4 mmol/L ± 12%).

CONCLUSION

A small proportion of lactate specimens may experience delay in processing. Although lactate levels may incrementally increase over 48-h at room temperature in unspun NaF/KOx collection tubes, the changes may not be clinically impactful.

Age and sex dependent reference intervals for random plasma/serum glucose concentrations related to different sampling devices and determined by an indirect procedure with data mining

The glucose concentration in plasma or serum is one of the most often requested analytical values in laboratory medicine. Whereas the analytical part of the glucose determination is well standardised, the standardisation of the pre-examination part (pre-analytical phase) is not sufficiently solved, yet. In view of the present controversial discussion regarding the most efficient prevention of pre-analytical glycolysis, the question arises whether the economical and logistic expenses for inhibiting glycolysis determining random glucose concentration are justified. In hospitals with adequate logistics (e.g. pneumatic tube systems for blood tubes) to guarantee a blood sample transport time of about 1 – 2 h, plasma or serum without prevention of glycolysis can be applied for random glucose concentrations if the reference limits are estimated by the laboratory. If such logistics are not available, especially in primary care services, either plasma or serum samples or whole blood in special tubes with anti-glycolytic additives may be sent to the laboratory.