Reliability of quantitative and qualitative tests to identify heterozygotes carrying severe or mild G6PD deficiency

OBJECTIVES

To determine if the qualitative test (cytochemical) is more reliable than the quantitative test (differential pH-metry) in identifying heterozygous G6PD- subjects.

DESIGN AND METHODS

Identification of heterozygous G6PD- subjects was done by the measurement of G6PD activity and by a cytochemical test.

RESULTS

A cytochemical test is more sensitive than differential pH-metry to identify heterozygous G6PD- subjects.

CONCLUSIONS

A cytochemical test is a reliable method for mass screening for G6PD deficiency to identify G6PD- heterozygotes.

Application of a new chemiluminescence method for the determination of glucose-6-phosphate dehydrogenase activity in healthy and enzyme-deficient individuals

INTRODUCTION

A chemiluminescence (CL) technique, which determines the glucose-6-phosphate dehydrogenase (G-6-PD) activities in healthy, heterozygous, and completely enzyme-deficient individuals was applied.

METHODS

CL intensities were detected for 4 h at 15-min intervals in each sample with or without addition of G-6-PD substrates into the reaction mixture.

RESULTS

The results revealed an inverse correlation to the reference UV method (Zinkham method; r=-0.80). Furthermore, the CL assay was able to detect G-6-PD activities as low as 0.2 IU/gHb, which was not possible by the UV method.

DISCUSSION

In conclusion, we believe that this method offers a new diagnostic tool for the detection of G-6-PD activities in enzyme-deficient individuals and, because of its increased sensitivity, makes it amenable for determining the effects of different pharmaceutical agents on G-6-PD activity in tissue or cell cultures.

G6PD/PK ratio: a reliable parameter to identify glucose-6-phosphate dehydrogenase deficiency associated with microcytic anemia in heterozygous subjects

OBJECTIVES

To determine if measuring the ratio of glucose-6-phosphate dehydrogenase (G6PD) to pyruvate kinase (PK) is more reliable than only measuring G6PD activity to identify heterozygous G6PD- individuals with associated microcytic anemia in the Calabrian population, which shows high frequencies of both the thalassaemia (thal) trait and G6PD deficiency.

DESIGN AND METHODS

Measurement of G6PD and PK activities was carried out on 205 samples of whole blood from Calabrian subjects of both sexes (age range 10-50 years) using a double starter differential pH-metry technique.

RESULTS

The G6PD/PK ratio is able to differentiate G6PD- heterozygous individuals from the normal population. G6PD/PK values also allowed us to easily identify the G6PD- heterozygous subjects with microcytic anaemia. Student's t test shows that G6PD/PK ratio is more reliable in both sample groups, relative to G6PD activity in normal subjects.

CONCLUSIONS

G6PD/PK ratio is a reliable diagnostic parameter for mass screening for G6PD deficiency.

Identification of glucose 6-phosphate dehydrogenase deficiency in a population with a high frequency of thalassemia

High frequencies of both thalassemia trait (5.2%) and glucose 6-phosphate dehydrogenase (G6PD) deficiency for only males (1.3%) have been observed in the Calabrian population. The G6PD activity measurement was carried out on 1239 samples of whole blood from Calabrian subjects of both sexes (age range 10-55) by a differential pH-metry technique which was quite suitable to determine the G6PD deficiency in mass screenings. The analyzed subjects showed: only the thalassemia trait; or only the G6PD deficiency; or only the total iron serum deficiency; or G6PD deficiency associated with the thalassemia trait or with the total iron serum deficiency. The G6PD heterozygous subjects have an enzymatic activity which is masked by both the thalassemia trait and the total iron serum deficiency. In a population showing high frequencies of both thalassemia trait and G6PD deficiency, the comparison of G6PD activity of heterozygous subjects also affected with the thalassemia trait is more reliable if referred to the enzymatic activity of the carriers of the latter inherited anomaly rather than to G6PD activity of normal subjects.

The application of the differential pH method to the biochemical evaluation of seminal plasma

OBJECTIVE

To apply the differential pH method to the biochemical evaluation of seminal plasma.

DESIGN AND METHODS

Fructose, citric acid and free L-carnitine concentration in human seminal plasma were measured by the differential pH method. These are routinely taken as markers of seminal vesicle, prostate and epididymal function, respectively. The pH differential method was then compared with standard spectrophotometry.

RESULTS

The linearity, recovery and imprecision calculation for each assay were found to be reliable and the method correlated well with the reference spectrophotometric technique. In addition, the pH differential method showed certain advantages compared to spectrophotometry: a) speed of procedure (40 to 120 sec/assay); b) ability to measure the analytes even in small volumes of seminal plasma (10 microL to 50 microL) without deproteinization or dilution, thus eliminating manual operations.

CONCLUSIONS

The differential pH method is an innovative approach to the biochemical assessment of seminal plasma.

Simultaneous automated determination of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase activities in whole blood

We report a potentiometric fully automated method for determining red cell glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase activities and the glucose 6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase index using 25 microliters of whole blood. No sample pre-treatment (e.g., preparation of the haemolysate) is needed and the measurements are performed at pH 8.0 and 37 degrees C under the conditions recommended by the ICSH committee. The reproducibility was constantly good, with within-run CV of 1.0% (glucose 6-phosphate dehydrogenase) and 5.9% (glucose 6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase) for activities in glucose 6-phosphate dehydrogenase non-deficient adults, and of 2.3% (glucose 6-phosphate dehydrogenase, G6PD) and 2.5% (glucose 6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase) for G6PDMediterranean heterozygotes. Linearity was observed up to an activity of 2800 U/l of glucose 6-phosphate dehydrogenase. Results of glucose 6-phosphate dehydrogenase activity (U/l) in whole blood (y) correlated well with those obtained with the previously described monostarter assay, performed at pH 9.2 (y = 0.60x + 37; n = 80; r = 0.991). Results of 6-phosphogluconate dehydrogenase (U/l) in whole blood (y) correlated well with those obtained by the ICSH recommended method (x) (y = 0.779x - 44; n = 23; r = 0.991). Reference intervals are reported for glucose 6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase and glucose 6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase index relatively to normal, beta- and alpha-thalassaemic glucose 6-phosphate dehydrogenase non-deficient adults, to glucose 6-phosphate dehydrogenase deficient adult males and to G6PDMediterranean non-thalassaemic heterozygotes. We demonstrate that the diagnostic sensitivity of the glucose 6-phosphate dehydrogenase/6-phosphogluconate dehydrogenase index in detecting the G6PDMediterranean heterozygotes is superior to that of the glucose 6-phosphate dehydrogenase activity alone.

Whole blood L-lactate assay by a new differential pH method: application to metabolic investigations

We propose a new quantitative method for L-lactate assay in whole blood, based on the measurement of pH variation caused by specific and irreversible oxidation of L-lactate to pyruvate in the presence of an electron acceptor (hexacyanoferrate) and of the enzyme cytochrome b2 (EC 1.1.2.3.). No sample pretreatment is needed; the method is simple and fast (1.5 min/analysis) and requires 10 microliters whole blood per assay. Linearity is confirmed up to 20 mmol/l L-lactate. Within-day and between-day variability was (as C.V.) 3.6% and 8.1% for blood lactate 1.3 and 1.0 mmol/l, respectively. The results by the present method correlate well with those from two reference methods (test method vs a lactate sensor based method: r = 0.996; test method vs a spectrophotometric method: r = 0.987). An application of the present method to the continuous monitoring of L-lactate in patients after combined kidney and pancreas transplantation, under conditions of euglycemic hyperinsulinemia and hyperglycemic hyperinsulinemia is reported. We conclude that the method is simple and reproducible and can be employed to measure whole blood lactate concentration continuously both in clinical protocols and in basic research.