Colorimetric measurement of plasma lactate.

A rapid and simple enzymatic method for plasma lactate is proposed using stable reagents to produce the formazan color. This method agrees well with a reference kit method, r = 0.955 and the regression equation is y = 0.99x + 0.09. The over-all recovery averages 100%, with a precision ranging from 0.6 to 3.3%. No interferences have been shown with the formazan reaction. The proposed method is inexpensive, ideal for batch analyses, and is an attractive method for the busy clinical laboratory.

Importance of postmortem changes in measurements of thyroid function in studies of sudden infant death syndrome.

Various measurements of thyroid function were made from serum sampled at necropsy by cardiac puncture in adults and compared with the equivalent values before death. There were significant increases in serum total T3 (0.66 before death, 1.14 nmol/l after death), free T3 (0.82 to 1.52 pmol/l), and reverse T3 (1.12 to 1.75 nmol/l); and significant decreases in total T4 (73.7 to 56.6 nmol/l), free thyroxine index (FTI) (83.2 to 56.6), and free T4 (14.2 to 11.9 pmol/l). The increase in serum T3, presumably from T4 deiodination after death, observed in this study may explain the increased T3 concentration reported in serum sampled from cases of sudden infant death syndrome (SIDS).

Colonic bicarbonate output as a test of disease activity in ulcerative colitis.

No available test objectively measures impairment of function of the inflamed colonic mucosa in ulcerative colitis. To study function we assessed rectal bicarbonate output by rectal dialysis in the presence of water and bacterial fatty acid (n-butyrate) in 21 controls, 18 patients with acute ulcerative colitis, 12 patients with ulcerative colitis in remission, and 12 patients with other forms of colitis. In acute ulcerative colitis, compared with controls, bicarbonate output and pH was reduced (p less than 0.001); stimulated bicarbonate output with bacterial fatty acid (incremental bicarbonate output) was reduced by 80% in acute ulcerative colitis (p less than 0.01). Results indicate that bicarbonate output is a useful and selective test of mucosal function in acute ulcerative colitis. A diminished incremental bicarbonate output with n-butyrate supports the view of inadequate oxidation of bacterial fatty acids in vivo by the mucosa in ulcerative colitis. Whether the test will prove to be an index of prognosis or will aid choice between medical or surgical therapy requires further study.

Hypocortisolaemia and adrenocortical responsiveness at onset of septic shock.

OBJECTIVE: To characterise the plasma cortisol profile and adreno-cortial responsiveness (short Synacthen test) of patients in septic shock. DESIGN: Retrospective assessment using case-notes and ICU charts. SETTING: University teaching hospital ICU. PATIENTS: 68 septic shock patients with plasma cortisol and/or short Synacthen test measured at ICU-admission or onset of shock post ICU-admission. Patients were identified from a total population of 155 patients who had PCL and/or SST measured over a 4.5 year period. INTERVENTION: None. MEASUREMENTS AND RESULTS: Patients with septic shock had a plasma cortisol ranging from 210-8900 nmol/l and mortality of 56%. There were 22 (32%) below (low) and 46 (68%) above (high) a 'critical' plasma cortisol of 500 nmol/l. Using stepwise logistic regression, mortality was adequately predicted by and increased with, increasing plasma cortisol and onset of shock remote from ICU-admission. Short Synacthen tests were available in 33 patients: 11 responders (cortisol increment > 200 nmol/l above baseline 30 min after 0.25 mg intravenous Synacthen) and 22 hypo-responders. Mortality in patients was adequately predicted by and increased with a decrease in cortisol increment post-Synacthen. Thirteen patients (plasma cortisol 606 +/- [SD] 297 nmol/l) had complete haemodynamic profiles before inotropic therapy; no relationship was demonstrated between plasma cortisol and circulatory variables. Follow-up revealed no cases of Addison's disease. CONCLUSIONS: In septic shock, 'hypocortisolaemia' is not uncommon and does not predict a high mortality; adrenocortical hypo-responsiveness may be associated with poor outcome.

Colorimetric measurement of D(-)lactate in plasma.

We describe a method for the direct assay of D(-)lactate in plasma using D(-)lactate dehydrogenase and a color reagent to produce a formazan color measured at 510 nm. This method agrees well with a modified lactate UV end-point method r = 0.998 and the regression equation y = 0.974x + 0.13. The precision for low and high concentrations of D(-)lactate is 4.8% and 3.6% within-batch and 8.9% and 1.7% between-batch. Recoveries average 105% and 98% for D(-)lactate at concentrations of 1 and 5 mmol/L, respectively. The proposed method is inexpensive and suitable for routine and emergency use, and shares reagents used for the assay of L(+)lactate and 3-hydroxybutyrate.

Stability of the CK-MB isoenzyme on routine storage.

Unlike earlier studies on the stability of the CK-MB isoenzyme carried out on control sera and on semi-purified and purified CK isoenzymes, we have studied the stability of CK-MB measured electrophoretically in patient sera under different laboratory storage conditions. The values obtained if the test was done immediately were significantly higher than those done on stored samples. There was no difference between specimens stored at -20 degrees C overnight or kept at room temperature (RT) for a few hours, but values were significantly lower (p less than 0.005) in specimens left at RT for 6 h and then stored overnight at 4 degrees C. To determine the effects of longer storage, further specimens stored either at -20 degrees C or at 4 degrees C for up to 4 days were also tested for CK-MB stability by electrophoresis and by immunoinhibition and immunoenzymetric methods. The immunological methods were included in the study to assess method dependency of CK-MB stability. CK-MB was stable at -20 degrees C by all methods, but at 4 degrees C, CK-MB was stable only by immunological and not by electrophoretic (p less than 0.005) measurement. Specimens stored under adverse conditions (4-6 days at RT) showed 50% deterioration of CK-MB when measured electrophoretically but only about 20% when measured immunologically.

Atypical LD isoenzymes with five diffuse bands and evidence for two types of binding.

We describe a plasma LD isoenzyme pattern in which all five bands are unusually diffuse and of retarded mobility, an appearance not previously reported. This was shown to be due to binding to immunoglobulin G from which the enzyme could be displaced by an antiserum to gamma chains. Protein A-Sepharose removed most of the LD activity from plasma but did not dissociate the complex, indicating that the Fab end of the Ig molecule was involved in binding. Antiserum to kappa chains displaced LD5 from the complex but had no effect on the anodal bands. By contrast NAD displaced the anodal isoenzymes but not LD5. We suggest that two types of binding are involved. The LD5 complex appears to represent a true antigen-antibody reaction whereas the binding to the faster isoenzymes does not. We also suggest that immunoprecipitation is more reliable than immunoelectrophoresis or immunodiffusion for demonstrating IgG in such complexes and may be of value in defining the nature of binding.

Placebo-controlled trial of dexamethasone for chronic biliary pain after cholecystectomy.

Activation of the sympathetic nervous system appears to be relevant in some patients with unexplained pain after cholecystectomy, particularly those who show increases in plasma transaminase activity after challenge with morphine (morphine responders). In this study, the hypothesis that dexamethasone would improve chronic biliary pain, perhaps by suppressing activation of the sympathetic nervous system, was tested in a double-blind, placebo-controlled, cross-over trial in 20 patients, 10 morphine responders and 10 nonresponders. Before treatment with dexamethasone and placebo, urinary excretion of norepinephrine (NE) was significantly higher (p less than 0.05) in morphine responders than in nonresponders. During treatment with dexamethasone, 1 mg each night for 4 weeks, neither morphine responders nor nonresponders showed a significant improvement in pain or nausea or a significant reduction in sympathoadrenomedullary activity as assessed by urinary excretion of catecholamines. At the dose administered, dexamethasone was unhelpful for chronic pain after cholecystectomy and did not result in suppression of the sympathetic nervous system as assessed by urinary excretion of NE.

Clinching the diagnosis: using the biochemical profile.

The biochemical profile is an important extension of clinical evaluation and should include widely applicable tests for this purpose. Interpretation of results requires a proper understanding of what constitutes normality and abnormality and a knowledge of how changes may occur. The pathologist has a major responsibility in advising on interpretation in different clinical situations. This requires a familiarity with artefactual and drug-induced changes and a thorough knowledge of the pathophysiology of disease processes.

Reliability of the porphobilinogen screening assay.

A survey conducted by the Australian Association of Clinical Biochemists Porphyrin Working Party on urinary porphobilinogen screening showed good sensitivity (75-97.5%). This is contrary to reports in the literature and to our own observations. We therefore assessed a widely used screening method (Watson-Schwartz) and found poor sensitivity (40-69%), and even less sensitivity (28-53%) when the urine samples were normally coloured or concentrated. Thus the results obtained by the Working Party might mislead one to infer that the Watson-Schwartz method is reliable.

The introduction of SI units and the standardisation of laboratory reports: recommendations of the South African Association of Clinical Biochemists.

The change of SI units in laboratory reporting is occurring in South Africa. To assist this process and to ensure uniformity among laboratories, the Recommendations of the South African Association of Clinical Biochemists are presented. Controversial points are discussed and subunits selected. A standardised format of laboratory reports is suggested.

Free thyroxine index or effective thyroxine ratio?

The ability of the free thyroxine index (FTI) and the effective thyroxine ratio (ETR) to distinguish abnormal from normal thyroid function is compared in a series of 422 patients; they were equally successful in detecting hyperthyroidism. In hypothyroidism, however, the ETR values of 22% were within 95% 'normal' limits compared with 7,4% of the FTI values. Other authors have shown a similar poorer sensitivity of the ETR compared with the FTI.