[Agreement in the determination of electrolytes in samples of serum and plasma. Stability of these samples kept for 2 hours at room temperature with uncovered tubes]. / Détermination des électrolytes dans des échantillons de sérum et de plasma, et stabilité dans des tubes ouverts pendant 2 heures à température ambiante.

UNLABELLED: The determination of electrolytes in the clinical laboratories is carried out in samples of serum or plasma in situations that tubes remain open during a lingering time. OBJECTIVE: To estimate the agreement and the interchangeability in the determination of electrolytes for three types of tubes (serum with separator, plasma with and without separator) in samples that remain at room temperature and open up to two hours. MATERIAL AND METHODS: Samples of 36 voluntary patients were selected determining the levels of sodium, potassium, chlorine, calcium, magnesium and phosphate in the three tubes on time 0 (basal), 60 and 120 minutes. The agreement was estimated by means of the intraclass correlation coefficient (ICC) and the interchangeability of results by means of lineal regression. RESULTS: Agreement among the samples was very high with ICC higher than 0.9 in all basal determinations except for the potassium for which the presence of a constant systematic error was detected between serum and two tubes of plasma. The stability of the parameters is good in all the samples. CONCLUSIONS: It is possible the use of different types of tubes in the determination of electrolytes under the working conditions of the clinical laboratories. The determination of potassium needs to be corrected before the exchange of results obtained with serum and plasma. The stability in the two first hours is good in all the cases.

Effects of time, temperature and blood cell counts on levels of lactate in heparinized whole blood gas samples.

OBJECTIVE: To investigate whether lactate levels may vary in relation to time, substrate concentration and blood cells counts. METHODS: In this study 110 samples from the daily clinical routine blood samples were collected. Determinations of lactate were made at different times where the samples had not been left for more than 120 min at room temperature (24 degrees C) or in the fridge (4 degrees C). The influence of glucose and blood cells on lactate production was also estimated. The rate in change of concentration (slope) and the increase expected at the beginning (intercept) were estimated through linear regression using a longitudinal marginal method. RESULTS: The time-related change in lactate was significantly higher at room temperature (0.012 mmol L(-1) min(-1)) than at 4 degrees C (0.0035 mmol L(-1) min(-1)) (p<0.0001). There was a significantly positive relationship between blood cells (mainly leucocytes) and the rate of reaction at room temperature. CONCLUSIONS: A delay in the processing of a whole blood sample of more than 15 min at room temperature or an hour in the fridge entails an important overestimation of the initial lactate levels. Pronounced leucocytosis (higher than 6 x 10(10)/L) meaningfully cut down the stability period (10 min).

Caffeine test assessment for measuring liver function in critically ill patients.

Caffeine elimination was studied in 73 patients admitted to an intensive care unit, 33 of whom had liver disease. Mean plasma clearance of caffeine in patients with no liver disease (1.30 +/- 0.79 ml/kg/min) was significantly higher than in patients with liver disease (0.39 +/- 0.23 ml/kg/min). Mean half-life of caffeine in patients with liver disease (23.96 +/- 12.19 h) was significantly higher than in patients with no liver disease (7.25 +/- 3.04 h). No significant differences in distribution volumes were found. Receptor-operator curves (ROC) for plasma clearance and the half-life of elimination of caffeine showed a high diagnostic value. Therefore, the parameters for caffeine biotransformation, i.e. Cl and t1/2, are useful for assessing liver function in the population studied.