The influence of storage time and temperature on the measurement of serum, plasma and urine osmolality.

BACKGROUND: Many clinical laboratories require that specimens for serum and urine osmolality determination be processed within 3 h of sampling or need to arrive at the laboratory on ice. This protocol is based on the World Health Organization report on sample storage and stability, but the recommendation lacks good supporting data. We studied the effect of storage temperature and time on osmolality measurements. METHODS: Blood and urine samples were obtained from 16 patients and 25 healthy volunteers. Baseline serum, plasma and urine osmolality measurements were performed within 30 min. Measurements were then made at 3, 6, 12, 24 and 36 h on samples stored at 4-8℃ and room temperature. We compared baseline values with subsequent measurements and used difference plots to illustrate changes in osmolality. RESULTS: At 4-8℃, serum and plasma osmolality were stable for up to 36 h. At room temperature, serum and plasma osmolality were very stable for up to 12 h. At 24 and 36 h, changes from baseline osmolality were statistically significant and exceeded the total allowable error of 1.5% but not the reference change value of 4.1%. Urine osmolality was extremely stable at room temperature with a mean change of less than 1 mosmol/kg at 36 h. CONCLUSIONS: Serum and plasma samples can be stored at room temperature for up to 36 h before measuring osmolality. Cooling samples to 4-8℃ may be useful when delays in measurement beyond 12 h are anticipated. Urine osmolality is extremely stable for up to 36 h at room temperature.

Aluminium Monitoring in Occupational Health : a Mini Review

Aluminium (Al) is a commonly encountered metal that has proven deleterious health outcomes; including neurological; respiratory and other systemic effects. There is growing awareness of the need to identify workers who have an increased burden of Al in order to avoid further exposure and to institute remedial action as appropriate. This need requires accurate identification of such workers. This paper examines the metabolism of Al with the aim of suggesting effective biomonitoring methods

Testing for Drugs of Abuse: Part 1

Drugs of abuse are commonly encountered in the workplace and the occupational health specialist is often asked to perform and interpret tests to check for the presence of such substances. A clear understanding regarding the limitations of testing is required for this purpose as this field has many potential pitfalls. This is the first of two articles that provide a broad overview of the commonly encountered drugs of abuse (DOA); the biological samples that can be used; possible interferants and adulterants that may be encountered; and the role of the laboratory and pathologist. The second article in this series examines the technology involved; looking briefly at immunoassays and mass spectrometry; and issues regarding cut-points and interpretations

Testing for Drugs of Abuse - Part 2

This is the second article in this series. The first looked at some of the commonly encountered drugs of abuse; discussed the range of samples on offer; established why urine is the preferred matrix; and addressed methods of sample adulteration. Part 2 briefly discusses immunoassay technology; the means to comment on the integrity of a sample and issues regarding cut-points and interpretations. The necessity for confirmatory testing of positive test results is discussed and the use of a mass spectrometric method is recommended for this purpose

Assessing Lead Levels in Occupational Health : a Mini-Review

Lead is a well-established toxin that continues to pose a health risk. Blood lead levels (BLLs) and urinary chelatable lead are the tests of choice for assessing acute and chronic toxicity. We highlight some of the other tests available. As occupational exposure to lead is often accompanied by other toxic heavy metal exposure; measuring whole blood heavy metal levels should be considered for workers with chronically elevated BLLs

Mercury; the elusive heavy metal

Mercury is ubiquitous in the environment and therefore every human being; irrespective of age or location; is exposed to one form of mercury or another. The major source of environmental mercury is natural degassing of the earth's crust; whilst industrial activities can raise exposure to toxic levels directly or the through the use of liquid metals or synthesised mercurial compounds.1 Mercury still gives rise to accidental and occupational exposure. The aim of this mini review is to describe the main factors that influence mercury toxicity and provide a framework for the interpretation of mercury

Stability of red blood cell folate in whole blood and haemolysate.

BACKGROUND: Folate, a water soluble B vitamin, is necessary for normal cell growth and DNA synthesis. A deficiency leads to megaloblastic anaemia and possible neurological sequelae. Since we receive samples from distant clinics and experience problems due to the long transit times to our laboratory, we carried out a folate stability study. METHODS: Fasting blood samples were drawn from 40 healthy volunteers. We determined the baseline red blood cell (RBC) folate in duplicate on each sample. Half the sample was then stored at various temperatures prior to haemolysate formation and RBC folate was determined regularly to determine sample stability. The other half was haemolysed, the haemolysate stored at various temperatures and analysed regularly to determine haemolysate stability. A statistical test of equivalence was applied using 18% as a pre-defined limit. RESULTS: We found that whole blood was stable at 4 degrees C up to 72 hours. At room temperature stability has been proven up to 24 hours. Results of additional experiments with haemolysate support stability under all conditions for 12 hours. CONCLUSIONS: Samples for RBC folate determination transported from distant clinics are stable for up to 72 hours at 4 degrees C or at room temperature for at least 24 hours. The prepared haemolysates may be stored at -20 degrees C. Our experiments show that sample transportation at higher temperature does not affect folate stability within our predefined limits.