Effects of heating plasma at 56 degrees C for 30 min and at 60 degrees C for 60 min on routine biochemistry analytes.

Abstract

A number of viruses are known to cause haemorrhagic fever (VHF) and pose a risk of transmission to healthcare workers. These include Lassa fever, Congo±Crimean haemorrhagic fever, and Ebola and Marburg viruses. Because there is a high mortality rate in patients infected with these viruses, there are stringent recommendations in Australia for the care of suspected cases. Biochemistry laboratories in general are not equipped to handle highly infectious samples and there is a danger that aerosols produced by biochemistry analysers may spread the infection. There are no Australian or international guidelines for handling specimens from suspected VHF cases. Heating the plasma samples at 56 C for 30min largely inactivates the viruses, rendering them safe to process as routine diagnostic samples using standard laboratory precautions. Also, it has been reported that heating samples at 60 C for 60min will inactivate Congo±Crimean haemorrhagic and Ebola viruses. The aim of this study was to investigate changes in biochemistry results when plasma samples were heated at 56 C for 30min and at 60 C for 60min. Heparinized plasma samples were selected to cover a wide range of analyte concentrations from specimens stored at 4 C for less than 7 days. The following analytes were measured before and after heating (n=20); sodium, potassium, bicarbonate, urea, creatinine, urate, total protein, albumin, total bilirubin, alkaline phosphatase (ALP), alanine aminotransferase (ALT), aspartate aminotransferase (AST), glutamyl transferase (GGT), creatine kinase (CK), cardiac troponin I (cTnI), glucose, amylase, total calcium, magnesium, inorganic phosphate and C-reactive protein (CRP). All except cTnI were analysed on a Hitachi 917 analyser using standard biochemical methods. Cardiac TnI was analysed on an ACS 180 analyser. The concentrations of analytes after heating were expressed as a percentage of preheating concentrations. Heating plasma samples at 56 C for 30min resulted in a mean change of 0±6% in the concentrations of all the measured analytes except for cTnI and the enzymes ALP, ALT, GGT and CK (Table 1). Heating at 60 C for 60min showed a 7±12% change in the concentrations of bicarbonate, total protein, albumin, total calcium and phosphate, and a 26% and 21% reduction in the activities of AST and amylase, respectively. There was a mean reduction of 73±100% in the concentrations of cTnI, ALP, ALT, GGT and CK. The percentage changes in the rest of the analytes ranged from 0 to 6%. In conclusion, we propose the following guidelines for handling specimens for biochemistry tests from suspected cases of VHF. Blood specimens must be taken and transported to a designated receiving area with appropriate precautions; the specimens be centrifuged in a category 3 biological safety cabinet; the separated plasma be heated at 60 C for 60min and then passed on to the biochemists for analysis. This will reduce the risk for the laboratory staff and the biochemistry analysers will not require disinfection. The results of tests after heating are acceptable for electrolytes (sodium, potassium and magnesium), renal function (urea, creatinine and urate), liver function (bilirubin), glucose and CRP. Acute hepatocellular damage will easily be detected, as the mean reduction in AST postheating was 26%. Bicarbonate concentration within the reference interval excludes metabolic acidosis. Only elevated values of cTnI and amylase are of diagnostic value. Cardiac TnI and amylase levels within the reference intervals do not exclude myocardial damage or acute pancreatitis. The results for total calcium, phosphate, albumin and total protein are of limited use, and it is not worthwhile measuring ALP, ALT, GGT and CK. Short Report Ann Clin Biochem 2000; 37: 802±804