Biochemical analysis of ascitic (peritoneal) fluid: what should we measure?

Ascitic fluid samples are frequently sent to the laboratory for analysis. Although the underlying cause of the ascites is often thought to be clinically obvious, it is important to establish a definitive diagnosis. The value of a cell count and bacterial culture of the ascitic fluid is not disputed, but the role of biochemical testing is less clear. The use of ascitic fluid total protein to try to classify ascitic fluids as either an exudate or a transudate has contributed to this. The use of the physiologically based serum ascites albumin gradient to differentiate ascites caused by portal hypertension from other causes provides a better diagnostic approach. We recommend that the serum ascites albumin gradient is performed by laboratories as the first-line test and that interpretative reports are provided. Additional testing should be restricted to specific diagnostic queries and requires close collaboration between the laboratory and the clinician.

Non-specialist management of acute renal failure.

In a 12-month prospective study of the initial management of patients with acute renal failure (ARF) in East Kent (population 593 000), we evaluated the initial management of ARF and assessed what proportion of ARF may have been preventable. Patients were seen and assessed on a daily basis, and were followed until discharge from hospital or death; survivors were subsequently followed for 3 years. Overall, 288 patients developed ARF (486 per million population/year). Mean age at presentation was 73 years (range 14-96). Initial assessment was often suboptimal, and key features in investigation and initial management were often lacking. In 108 cases, ARF was iatrogenic and/or potentially preventable (53 preventable, 99 iatrogenic, 44 both). Overall survival was 56% at discharge from hospital, 35% at 1-year follow-up, 31% at 2 years, and 28% at 3 years. In discharged patients, recovery of function was complete in 69%. A significant proportion of ARF is preventable. Clear guidelines, easily accessible at the point of care, could aid the diagnostic evaluation of the patient with ARF and indicate where referral for a specialist opinion is appropriate.

Biochemical analysis of pleural fluid: what should we measure?

Biochemical examination of pleural fluid is usually done to try to identify the cause of a pleural effusion. The various analytes that have been suggested for this are reviewed and evaluated. Distinguishing whether the effusion is an exudate or transudate is a pragmatic first step. with further investigations dictated by the clinical features and these results. Total protein and lactate dehydrogenase were used first; Light's criteria were published in 1972 and since then additional markers including cholesterol, bilirubin and albumin gradient plus combinations of these have been proposed. Although combination testing does improve the sensitivity for diagnosis of an exudate. this is at the expense of specificity. Measurement of fluid to serum ratios appears to confer no advantage, and if a single test is required total protein performs as well as any. Additional tests may be useful in specific circumstances: pleural fluid pH may aid decisions over drainage of a parapneumonic effusion; glucose may indicate an effusion associated with rheumatoid arthritis; and adenosine deaminase may help with the diagnosis of tuberculous effusions.

Laboratory blunders revisited.

Blunders which occurred over a 1 year period in the clinical chemistry departments of two health districts were recorded and categorized according to type and detection stage. A blunder was defined as an incident leading to an incorrect result/set of results either being reported or detected at the final checking-out stage in the laboratory. Of the total of 120 blunders--which is a blunder rate of less than 0.1% of requests--53 (44%) were detected at the final checking-out stage. Blunders detected after the report had left the laboratory were divided into those subsequently picked up by laboratory personnel (23); those detected by clinicians (19); and those by external quality assessment schemes (21). The types of blunder were fairly equally distributed between the booking-in (36), analysis (38), and reporting (35) stages of the laboratory process. A formal review of blunders detected in laboratories is a valuable aid to overall performance.

18-Hydroxycorticosterone as a marker for primary hyperaldosteronism.

An assay for the measurement of 18-hydroxycorticosterone (18-OHB) in plasma has been validated. The method involves extraction of plasma with dichloromethane, thin layer chromatography and radioimmunoassay with an iodinated 18-hydroxycorticosterone-3-carboxymethyloxime ligand. The plasma concentration of 18-OHB was measured in 16 patients with primary hyperaldosteronism and 20 control subjects. After overnight recumbency a significantly higher mean concentration of 18-OHB was found in the samples taken from the patients than in those from the control subjects. The degree of elevation did not clearly discriminate between patients with a unilateral adenoma and those with bilateral adrenal hyperplasia. A significant anomalous postural decrease in the 18-OHB concentration occurred in 10 of the 13 patients with an adenoma, whereas there was a significant postural increase in the three patients with hyperplasia.

Low dose infusion of atrial natriuretic peptide causes salt and water excretion in normal man.

1. The effects of low dose infusion of atrial natriuretic peptide (ANP) were observed in double-blind, placebo-controlled study in six fluid-loaded volunteers. After baseline observations, hourly increments of 0.4, 2 and 10 pmol min-1 kg-1 were infused with continuous observation of heart rate, blood pressure and cardiac output. Plasma ANP, aldosterone, and catecholamines, and urinary volume and sodium excretion, were estimated at half-hourly intervals. 2. ANP infusion resulted in an increase of 35, 98 and 207% in urinary sodium excretion and of 10, 20 and 71% in urinary volume when compared with placebo. Plasma ANP was markedly elevated above placebo levels only during infusion of 10 pmol of ANP min-1 kg-1. 3. No change in heart rate of blood pressure was noted during the study, but a significant fall in stroke volume index was observed during active treatment. Plasma levels of aldosterone and catecholamines were not significantly different on the 2 treatment days. 4. The potent natriuretic and diuretic effects of this peptide at plasma concentrations not significantly elevated from physiological suggest a hormonal role for ANP in the homoeostasis of salt and water balance.

Angiotensin-converting enzyme and its clinical significance--a review.

There have been considerable advances in understanding the metabolic role of the endothelial lining cells of the blood vessels. Angiotensin-converting enzyme activity is concentrated in these cells, especially those lining the pulmonary circulation. The enzyme exerts control over systemic vascular tone indirectly through the powerful pressor effect of angiotensin II. A number of therapeutic agents are now available which directly inhibit converting enzyme activity and thereby effect a reduction in blood pressure. Macrophages are the source of increased angiotensin-converting enzyme activity commonly found in association with active sarcoidosis. A better understanding of this phenomenon may give fresh insight into this puzzling condition. Pulmonary endothelial metabolism is affected by lung injury and it is likely that in this situation changing activities of serum angiotensin converting enzyme may indicate the extent of damage and the response to therapy. The full clinical significance of serum ACE measurements has yet to be established. However, raised activities have been reported in a number of other conditions and diabetes mellitus and hyperthyroidism are of particular current interest. The numerous methods and reference ranges described in the literature for the measurement of serum ACE activity require further assessment, and there is a clear need for an accepted reference method.