Comparison of macro- and micro-lightguide spectrophotometric measurements of microvascular haemoglobin oxygenation in the tuberculin reaction in normal human skin.

The changes in haemoglobin oxygenation (SO2) occurring in the tuberculin reaction in human skin were measured using macro- and micro-lightguide spectrophotometry and the results compared. A significant difference was found between the measurements from the respective instruments, demonstrating that the micro-lightguide technique measures only in the most superficial capillaries. Laser Doppler flux (LDF) and transcutaneous oxygen (tcpO2) measurements were also obtained concurrently. At the height of the reaction, heating did not significantly change SO2 or LDF, showing that the vessels in the skin were maximally vasodilated. Although SO2 was increased in the reaction, tcpO2 decreased. This suggests that the infiltrating cells may present a diffusion barrier to oxygen between the capillaries and the tissue cells. This study has shown that micro-lightguide spectrophotometry gives a local picture of intracapillary oxygen supply, which is useful in elucidating the pathophysiological changes occurring during chronic inflammation.

Clinical evaluation and use of urine screening for drug abuse.

Urine drug screening is indicated to evaluate patients who show mental status or behavioral changes and to monitor the abstinence of drug abusers. The appropriate timing for collecting urine specimens may vary depending on the suspected drug of abuse and on laboratory factors. Laboratories use a variety of techniques to do urine screens, and these must be understood by clinicians ordering the screens to interpret results correctly. In treating drug-abusing patients, clinicians must apply structured reinforcement in conjunction with urine screen results to aid patients in achieving abstinence.

Differentiation of renal from non-renal hematuria by microscopic examination of erythrocytes in urine.

Recent studies indicate that hematuria of renal parenchymal origin can be differentiated from hematuria of other origin by the presence of dysmorphic urinary erythrocytes (cells exhibiting irregular membranes or small surface blebs). We investigated the utility of this simple screening assay in a routine clinical laboratory. Dysmorphic erythrocytes in urine from 69 patients (18 with renal-parenchymal disease) were quantified on unstained slides by medical technologists using phase-contrast microscopes. Samples stored at 4 degrees C or 23 degrees C for up to 5 h had no significant changes in percentages of dysmorphic erythrocytes (PDE). PDE was also not modified by urea nitrogen concentration, osmolality, or pH over the physiological ranges of these variables. Receiver-operating characteristic (ROC) curves indicated an optimal sensitivity of 88% and specifity of 94% at a decision level of 14% dysmorphic erythrocytes per high-power field. Thus, the presence of fewer than 14% dysmorphic cells is suggestive of extra-renal disease; more than 14% is suggestive of intra-renal disease.

Influenza vaccination and warfarin anticoagulation.

Because influenza vaccine can markedly depress hepatic cytochrome P450 activity and may have caused an extreme prolongation of the prothrombin time in one patient receiving warfarin, we studied the effect of influenza vaccine on anticoagulation in 21 male outpatients receiving chronic warfarin therapy. Prothrombin times measured three to five times in the month after vaccination were in the therapeutic range as often as those measured before vaccination. Mean changes in prothrombin times measured after vaccination were not significantly different from those on the day of vaccination or in the 3 months before vaccination. The size of this study assured an 80% chance that any deviation from the observed mean prothrombin times would not exceed 2.1 s. No patient had any bleeding or thromboembolic problems. Thus, influenza vaccination of patients anticoagulated with warfarin appears to be safe.

Visceral protein status of patients hospitalized for alcoholism.

The purpose of this study was to evaluate the nutritional status of patients hospitalized for alcoholic rehabilitation. It was hypothesized that thyroxine-binding prealbumin, due to its shorter half-life, would be more sensitive to poor nutritional status than other visceral proteins. Extensive biochemical, anthropometric, and nutrient intake data were obtained on hospital days 2, 7, and 14. No abnormalities in visceral protein status initially, or with time, were seen in this population. The principal conclusion is that severe nutritional deficiencies are not prevalent in this patient sample hospitalized for alcoholic rehabilitation.

Effect of hemodialysis on the pharmacokinetics of theophylline in chronic renal failure.

We studied theophylline elimination in 8 patients with chronic renal failure to determine the effect of hemodialysis on the pharmacokinetics of theophylline. Each subject was studied twice, once on a nondialysis day and again during dialysis. Total body theophylline clearance on the nondialysis day was similar to that reported for patients with normal renal function (57.4 +/- 27.2 ml/kg/h). Hemodialysis accelerated theophylline elimination and shortened serum theophylline half-life in all patients (nondialysis t 1/2 = 7.3 h +/- 2.3 vs. dialysis t 1/2 = 2.7 +/- 0.9 h, p less than 0.01). Dialysis clearance averaged 59.7 +/- 16.4 ml/kg/h with a fraction of drug removed of 0.4 liters in 4 h. Guidelines for theophylline management during hemodialysis are suggested.

Performance characteristics of bioassay, radioenzymatic assay, homogeneous enzyme immunoassay, and high-performance liquid chromatographic determination of serum gentamicin.

We compared the accuracy, precision, and between-method error of the microbiological assay, the radioenzymatic assay, the homogeneous enzyme immunoassay, and the high-performance liquid chromatographic assay for the quantitation of gentamicin in serum. Precision and accuracy were evaluated by reference samples prepared to contain 0.0 to 32.7 micrograms of gentamicin per ml. Correlations between the methods utilized patient sera with gentamicin concentrations ranging from 0.6 to 13.3 micrograms/ml. All methods were reliable within acceptable limits for routine clinical use; intermethod correlation coefficients exceeded 0.96. Relative to the microbiological assay, the alternative methods offer the advantage of rapid analysis. The elapsed times for acquiring data on a set of 10 specimens under routine operating conditions were 0.5 h by the enzyme immunoassay, 4 h by the radioenzymatic assay, 5 h by the high-performance liquid chromatographic assay, and 10 h by the microbiological assay.

Potential liabilities of gentamicin homogeneous enzyme immunoassay.

We report two potential liabilities of the homogeneous enzyme immunoassay for the determination of serum gentamicin. One is a considerable loss of precision and accuracy at the ends of the calibration curve, and the other is an apparent loss of gentamicin with storage at -60 degrees C.

Use of equilibrated blood for internal blood-gas quality control.

We have used equilibrated human blood for blood-gas quality control since 1970. In blood equilibrated 24 h after shedding, gas tensions are stable for 4 to 6 h at 0 to 4 degrees C; each control specimen is analyzed several times during that period to resolve malfunctions, etc. Three-fourths of all errors in gas-tension measurement detected with equilibrated blood were detected with the highest-tension controls. Equilibrated blood controls signal about one error every 14 d on each instrument. For more complete quality control, we supplement analysis of equilibrated blood with other sorts of controls, comparing results obtained by assaying each patient's specimen on two instruments being our most effective adjunct. Such comparisons have identified erroneous assays in 3.9% of the specimens tested. The magnitude of interinstrument discrepancies (random errors) have ranged from 9 to 100% of the appropriate determinations. We use control data derived from equilibrated blood analysis for special management purposes (evaluating instruments, quantitating micro- vs. macro-sampling discrepancies, and decreasing instrument-repair costs).

Proficiency testing for blood-gas quality control.

We have conducted a voluntary, community blood-gas proficiency testing program, with use of tonometered human blood, for 32 analyzers located in 16 laboratories. Instruments initially showed inaccuracies as large as -30.8 to +17.3% for po(2), and -14.0 to +42.9% for pco(2), but inaccuracy and imprecision decreased in most laboratories during the program. For a typical 15-week period, mean group precision (CV) was 4.3 To 5.1% for po(2) from 6.92 to 33.3 Pa (52 to 250 mmHg), and 4.0 to 6.9% for pco(2) from 2.0 to 6.8 Pa (15 to 51 mmHg). This program can detect increasing imprecision or inaccuracy caused by analyzer deterioration, and can identify interlaboratory or interinstrument bias and problems not detected by participant quality-control programs. Participants have used the proficiency information in discussing data quality with clinicians, promoting internal control and maintenance programs, and justifying instrument purchases. We believe that proficiency-testing documentation of variability in blood-gas analysis may help to establish realistic patient-care protocols.