ABSTRACT
OBJECTIVE: To compare blood glucose control when using biphasic insulin aspart (BIAsp) three times a day (using 70/30 high-mix before breakfast and lunch), with biphasic human insulin (BHI, 30/70) twice daily in adults with type 2 diabetes already treated with insulin. RESEARCH DESIGN AND METHODS: In a 60-day, open-label, crossover study, people with insulin-treated type 2 diabetes [n = 38, baseline haemoglobin A1c 8.3 +/- 0.9 (s.d.) %] were randomized to BIAsp three times a day before meals, as BIAsp 70 (70% insulin aspart and 30% protamine-complexed insulin aspart) before breakfast and lunch and BIAsp 30 (30/70 free and protamine-complexed insulin aspart) before dinner, or to human premix insulin (BHI) 30/70 twice a day before meals. A 24-h in-patient plasma glucose profile was performed at the end of each 30-day treatment period. The total daily insulin dose of BIAsp regimen was 110% of BHI and the doses were not changed during the study. RESULTS: There was no difference between BIAsp and BHI in geometric weighted average serum glucose over 24 h [7.3 vs. 7.7 mmol/l, BIAsp/BHI ratio 0.95 (95% CI 0.88-1.02), not significant (NS)], but daytime geometric weighted average glucose concentration was significantly lower with the BIAsp regimen than with BHI [8.3 vs. 9.2 mmol/l, BIAsp/BHI ratio 0.90 (0.84-0.98), p = 0.014]. The mealtime serum glucose excursion was also lower with BIAsp than with BHI with statistically significant differences at lunchtime [difference -4.9 (-7.0 to -2.7) mmol/l, p = 0.000); the difference in glucose excursions above 7.0 mmol/l was also significant [-5.8 (-8.3 to -3.2) mmol/l, p = 0.000). The proportion of participants experiencing confirmed hypoglycaemic episodes was similar between regimens (42 vs. 43%, NS). CONCLUSIONS: An insulin regimen using high-mix BIAsp (BIAsp 70) before breakfast and lunch and BIAsp 30 before dinner can achieve lower blood glucose levels during the day through reduced mealtime glucose excursions in particular at lunchtime than a twice-daily premix regimen.
Subject(s)
Blood Glucose/drug effects , Diabetes Mellitus, Type 2/drug therapy , Hypoglycemic Agents/administration & dosage , Insulin/analogs & derivatives , Adult , Aged , Biphasic Insulins , Blood Glucose/metabolism , C-Peptide/blood , Cross-Over Studies , Diabetes Mellitus, Type 2/blood , Diabetes Mellitus, Type 2/complications , Drug Administration Schedule , England , Female , Humans , Hypoglycemia/etiology , Insulin/administration & dosage , Insulin Aspart , Insulin, Isophane , Male , Middle Aged , Treatment Outcome , Young AdultABSTRACT
OBJECTIVE: To determine the effect of adding nateglinide to therapy with insulin glargine in adults with Type 2 diabetes previously treated with insulin and with poor blood glucose control. RESEARCH DESIGN AND METHODS: In this 16-week, double-blind, placebo-controlled study, people with Type 2 diabetes [n = 55, HbA(1c) 8.2 +/- 1.0 (+/- sd)%, duration of diabetes 12.8 +/- 6.0 years, duration of insulin treatment 6.0 +/- 4.0 years] were transferred to single bedtime injection of insulin glargine for a titration period of 4 weeks, and then randomized to nateglinide or matching placebo before meals in addition to insulin glargine. Metformin was continued if taken. Doses of insulin and oral medication were titrated to protocol for the treatment period of 12 weeks. RESULTS: Baseline-adjusted self-monitored capillary blood glucose concentration at 12 weeks was significantly lower with nateglinide + insulin glargine compared with placebo + insulin glargine after breakfast [difference -2.3 (95% confidence interval -4.4, -0.2) mmol/l, P = 0.030], before lunch [-2.5 (-4.6, -0.3) mmol/l, P = 0.029], and after lunch [-2.3 (-4.3, -0.4) mmol/l, P = 0.021], but not at other times. Baseline-adjusted HbA(1c) was not lower with nateglinide + insulin glargine as compared with placebo + insulin glargine [7.8 +/- 1.4 vs. 8.3 +/- 1.0%, difference -0.43 (-0.98, 0.12)%]. CONCLUSIONS: Addition of nateglinide before meals to once-daily insulin glargine in people with long-standing diabetes already requiring insulin therapy improves blood glucose control in the early part of the day after breakfast and lunch, but does not provide good control of blood glucose levels overall.
Subject(s)
Blood Glucose/metabolism , Cyclohexanes/administration & dosage , Diabetes Mellitus, Type 2/drug therapy , Hypoglycemic Agents/administration & dosage , Insulin/analogs & derivatives , Phenylalanine/analogs & derivatives , Adult , Aged , Aged, 80 and over , Analysis of Variance , Blood Glucose/drug effects , Blood Glucose Self-Monitoring , Drug Administration Schedule , Drug Therapy, Combination , Female , Humans , Insulin/administration & dosage , Insulin Glargine , Insulin, Long-Acting , Male , Metformin/therapeutic use , Middle Aged , Nateglinide , Phenylalanine/administration & dosage , Time FactorsABSTRACT
AIM: To compare blood glucose control when using insulin glargine twice daily at breakfast- and dinner-times with insulin glargine once daily at dinner time, in unselected people with Type 1 diabetes using insulin aspart at meal-times. METHODS: In this 8-week, two-way, cross-over study, 20 people with Type 1 diabetes were randomized to insulin glargine injection once daily at dinner-time or twice daily at breakfast- and dinner-times, both plus meal-time insulin aspart. Each 4-week treatment period concluded with a 24-h inpatient metabolic profile. RESULTS: Insulin doses, HbA1c, fructosamine concentration and pre-breakfast self-monitored blood glucose (SMBG) concentration did not differ between treatment periods. SMBG concentrations after breakfast, after lunch and before dinner were lower with twice-daily compared with once-daily dinner-time glargine [9.3 +/- 0.5 (+/- se) vs. 6.7 +/- 0.5 mmol/l, P = 0.003; 10.2 +/- 0.9 vs. 7.0 +/- 0.9 mmol/l, P = 0.024; 9.6 +/- 0.5 vs. 6.6 +/- 0.5 mmol/l, P = 0.001]. Mean 24-h SMBG concentration was lower with twice-daily glargine (7.1 +/- 0.5 vs. 8.8 +/- 0.5 mmol/l, P = 0.031). Within-day variability of SMBG concentration was lower with twice-daily glargine (sd 3.2 +/- 0.2 vs. 4.0 +/- 0.3 mmol/l, P = 0.044). Plasma free insulin concentration was higher in the afternoon with twice-daily glargine (21.9 +/- 1.4 vs. 16.1 +/- 1.3 mU/l, P = 0.009), but lower overnight (12.1 +/- 1.7 vs. 17.8 +/- 1.7 mU/l, P = 0.030), compared with once-daily injection. Plasma glucose concentration overnight was higher with twice-daily compared with once-daily glargine (mean 9.0 +/- 0.4 vs. 6.6 +/- 0.4 mmol/l, P = 0.001). CONCLUSIONS: Blood glucose concentration rises in the late afternoon in association with falling plasma insulin levels towards the end of the 24-h period after insulin glargine injection in some people with Type 1 diabetes using once-daily glargine at dinner-time plus a rapid-acting insulin analogue at meal-times. This is prevented by twice-daily injection of insulin glargine.
Subject(s)
Diabetes Mellitus, Type 1/drug therapy , Hypoglycemic Agents/administration & dosage , Insulin/analogs & derivatives , Adolescent , Adult , Aged , Blood Glucose/metabolism , Cross-Over Studies , Diabetes Mellitus, Type 1/blood , Drug Administration Schedule , Female , Humans , Hypoglycemic Agents/blood , Insulin/administration & dosage , Insulin/blood , Insulin Glargine , Insulin, Long-Acting , Male , Middle Aged , Treatment OutcomeABSTRACT
AIMS: To compare blood glucose control using insulin glargine + insulin lispro with that on NPH insulin + unmodified human insulin in adults with Type 1 diabetes managed with a multiple injection regimen. METHODS: In this 32-week, five-centre, two-way cross-over study, people with Type 1 diabetes (n = 56, baseline HbA1c 8.0 +/- 0.8%) were randomized to evening insulin glargine + mealtime insulin lispro or to NPH insulin (once- or twice-daily) + mealtime unmodified human insulin. Each 16-week period concluded with a 24-h inpatient plasma glucose profile. RESULTS: HbA1c was lower with glargine + lispro than with NPH + human insulin [7.5 vs. 8.0%, difference -0.5 (95% CI -0.7, -0.3) %, P < 0.001]. This was confirmed by an 8% lower 24-h plasma glucose area under the curve (AUC) (187 vs. 203 mmol l(-1) h(-1), P = 0.037), a 24% reduction in plasma glucose AUC > 7.0 mmol/l1 (47 vs. 62 mmol l(-1) h(-1), P = 0.017) and a 15% lower post-prandial plasma glucose AUC (75 vs. 88 mmol l(-1) h(-1), P = 0.002). There was no reduction in night-time plasma glucose AUC or increase in plasma glucose area < 3.5 mmol/l. Monthly rate of nocturnal hypoglycaemia was reduced by 44% with glargine + lispro (0.66 vs. 1.18 episodes/month, P < 0.001). CONCLUSIONS: Compared with NPH insulin + unmodified human insulin, the combination of insulin glargine with a rapid-acting insulin analogue as multiple-injection therapy for Type 1 diabetes improves overall glycaemic control as assessed by HbA1c and 24-h plasma glucose monitoring to a clinically significant degree, together with a reduction in nocturnal hypoglycaemia.
Subject(s)
Blood Glucose/analysis , Diabetes Mellitus, Type 1/drug therapy , Hypoglycemic Agents/therapeutic use , Insulin/therapeutic use , Adult , Area Under Curve , Blood Glucose Self-Monitoring , Cross-Over Studies , Drug Therapy, Combination , Female , Glycated Hemoglobin/analysis , Humans , Hypoglycemia/blood , Hypoglycemic Agents/adverse effects , Insulin/adverse effects , Insulin/analogs & derivatives , Insulin Glargine , Insulin Lispro , Insulin, Isophane/adverse effects , Insulin, Isophane/therapeutic use , Insulin, Long-Acting , Male , Treatment OutcomeABSTRACT
AIMS: To compare blood glucose control when insulin glargine is given at lunch-time, dinner-time, and bed-time in people with Type 1 diabetes using insulin lispro at meal-times. METHODS: In this 16-week, three-way, cross-over study, 23 people with Type 1 diabetes were randomized to insulin glargine injection at lunch-time (L) [mean 12.37 +/- 00.34 (+/- sd) h], dinner-time (D) (18.12 +/- 00.40 h), or bed-time (B) (22.29 +/- 00.40 h), each plus meal-time insulin lispro. Each 4-week treatment period concluded with a 24-h inpatient metabolic profile. RESULTS: Insulin doses, HbA(1c), and fructosamine concentration did not differ between treatment periods. Pre-breakfast self-monitored blood glucose (SMBG) concentration was higher with injection of glargine at lunch-time than at other times [L: 9.2 +/- 0.3 (+/- se) vs. D: 8.2 +/- 0.3 or B: 8.0 +/- 0.3 mmol/l, P = 0.016], as probably was pre-lunch SMBG (L: 8.6 +/- 0.7 vs. D: 6.4 +/- 0.7 or B: 6.4 +/- 0.8 mmol/l, P = 0.051). Pre-dinner SMBG level was higher with dinner-time glargine than other injection times (D: 9.4 +/- 0.9 vs. L: 4.9 +/- 0.9 or B: 7.4 +/- 1.1 mmol/l, P = 0.007). For 22.00 to 02.00 h, mean inpatient plasma glucose concentration was higher with injection of glargine at bed-time than other times (B: 9.1 +/- 0.6 vs. L: 7.8 +/- 0.6 or D: 6.7 +/- 0.6 mmol/l, P = 0.023). Plasma free insulin concentration was lower at the end of the afternoon with dinner-time glargine than other injection times (D: 11.5 +/- 1.4 vs. L: 20.2 +/- 1.3 or B: 16.5 +/- 1.3 mU/l, P < 0.001). Frequency of hypoglycaemia was not different, but timing of hypoglycaemia differed between treatment periods. CONCLUSIONS: Blood glucose levels rise around the time of injection of insulin glargine whether given at lunch-time, dinner-time or bed-time. Bed-time injection leads to hyperglycaemia in the early part of the night which is improved by giving insulin glargine at lunch-time or dinner-time.
Subject(s)
Diabetes Mellitus, Type 1/drug therapy , Hypoglycemic Agents/administration & dosage , Insulin/analogs & derivatives , Adolescent , Adult , Aged , Blood Glucose/analysis , Blood Glucose Self-Monitoring/methods , Cross-Over Studies , Drug Administration Schedule , Eating , Female , Fructose/blood , Glycated Hemoglobin/analysis , Humans , Hypoglycemia/blood , Injections , Insulin/administration & dosage , Insulin/blood , Insulin Glargine , Insulin Lispro , Insulin, Long-Acting , Male , Middle Aged , Patient Satisfaction , Time FactorsABSTRACT
BACKGROUND: This retrospective study examined the efficacy of in-home father training on the communicative outcomes of children with autism. The in-home training consisted of two components: (1) expectant waiting; and (2) imitation with animation. METHODS: Efficacy of parent training was examined by measuring the ratio of utterances produced by the parents to the utterances produced by the children and the number of verbal imitation by the parents. Outcomes of the children's verbal production were examined by measuring the number of (1) single word utterances; (2) different words produced; and (3) verbal response to questions. RESULTS: Following training there was a decrease in the ratio of parent to child utterances and an increase in (1) the use of imitation by the parents; and (2) the number of single words and different words produced by the children. DISCUSSION: Results of this study suggested that the parents had learned to wait for their children to communicate verbally during communicative interactions and to interact more efficiently with their children by using verbal imitation. Overall, the results of this study support the efficacy of parent training that focuses on promotion of social reciprocity, and have important implications for clinicians and future research.
Subject(s)
Autistic Disorder/therapy , Communication , Fathers/education , Language Development Disorders/therapy , Language Therapy/education , Adult , Ambulatory Care , Child , Child, Preschool , Fathers/psychology , Female , Humans , Imitative Behavior , Language Development Disorders/psychology , Male , Middle Aged , Mothers/education , Mothers/psychology , Outcome and Process Assessment, Health Care , Parent-Child Relations , Verbal Behavior , Verbal LearningABSTRACT
OBJECTIVE: Lanreotide Autogel is a sustained-release aqueous gel formulation supplied in a prefilled syringe, with injection volume <0.5 ml. The aim of this study was to establish the efficacy and safety of Autogel in patients with acromegaly previously treated with octreotide LAR. DESIGN: A 28-week, open, multicentre study. PATIENTS: Twelve patients with acromegaly, treated with 20 mg octreotide LAR for >4 months, with serum GH levels <10.0 mU/l. METHODS: Autogel (90 mg) was given every 28 days during weeks 0-12. At week 16 the dose was titrated based on GH levels at weeks 8 and 12. If GH levels were <2.0, 2.0-5.0, or >5.0 mU/l, Autogel was reduced to 60 mg, maintained at 90 mg, or increased to 120 mg respectively, for the next three injections. GH and IGF-I levels were reassessed at weeks 24 and 28. RESULTS: Ten patients completed the study. Five remained on 90 mg Autogel throughout the study; in two patients the dose was reduced to 60 mg from week 16; in three patients it was increased to 120 mg. Mean GH levels were: baseline, 3.0+/-1.7 mU/l; week 12, 3.5+/-1.8 mU/l; week 28, 3.3+/-1.6 mU/l (NS). Mean IGF-I levels were: baseline, 212+/-70 microg/l; week 12, 185+/-91 microg/l; week 28: 154+/-61 microg/l (P=0.027). Six patients at baseline and eight at week 28 had normalised GH and IGF-I levels. Three patients reported adverse events: musculoskeletal pain (n=2) and injection-site symptoms (n=1). CONCLUSIONS: Lanreotide Autogel is effective and well tolerated in patients with acromegaly. This study in a small group of patients with well-controlled acromegaly suggests that the majority of patients switched from 20 mg LAR to 90 mg Autogel will have equivalent or better disease control.
Subject(s)
Acromegaly/drug therapy , Anti-Inflammatory Agents, Non-Steroidal/administration & dosage , Peptides, Cyclic/administration & dosage , Somatostatin/administration & dosage , Adult , Aged , Anti-Inflammatory Agents, Non-Steroidal/adverse effects , Anti-Inflammatory Agents, Non-Steroidal/blood , Antineoplastic Agents, Hormonal/therapeutic use , Delayed-Action Preparations , Female , Humans , Injections, Intramuscular , Male , Middle Aged , Octreotide/therapeutic use , Peptides, Cyclic/adverse effects , Peptides, Cyclic/blood , Somatostatin/adverse effects , Somatostatin/analogs & derivatives , Somatostatin/blood , Treatment OutcomeABSTRACT
Insulin glargine is a new extended-action insulin analogue, created by recombinant DNA modification of human insulin. Extension of the C-terminal of the B-chain with two arginine residues and the substitution of glycine for asparagine at position A-21 increases the isoelectric point, resulting in precipitation of the insulin at the injection site and a protracted absorption. Pharmacodynamic studies have demonstrated a prolonged metabolic profile without a pronounced peak and with a duration of action of 20 - 30 h. In clinical studies in people with Type 1 and Type 2 diabetes, insulin glargine has demonstrated improved pre-breakfast blood glucose control and a reduction in the frequency of hypoglycaemia, especially nocturnal hypoglycaemia, in comparison with neutral protamine hagedorn (NPH) insulin. In addition, 24h glycaemic control in Type 2 diabetes and treatment satisfaction may also be improved. However, whilst appearing achievable, insulin glargine has not yet demonstrated the ability to improve HbA(1c), though this may relate to inexperience in the use of the new compound. In order to fully exploit its metabolic advantages, it appears vital that the dose of insulin glargine should be titrated to achieve aggressive pre-breakfast blood glucose targets beyond those achievable with NPH in the absence of nocturnal hypoglycaemia. Insulin glargine appears to be a promising new addition to the insulin family and with increased experience in its use, especially in combination with rapid-acting insulin analogues, its full benefits may be realised. The use of insulin glargine with a rapid-acting insulin analogue brings us the closest we have ever been to providing the physiological insulin replacement that has long been awaited.
Subject(s)
Diabetes Mellitus/drug therapy , Hypoglycemic Agents/therapeutic use , Insulin/analogs & derivatives , Insulin/therapeutic use , Animals , Diabetes Complications , Humans , Insulin/adverse effects , Insulin/pharmacokinetics , Insulin/pharmacology , Insulin/toxicity , Insulin Glargine , Insulin, Long-ActingABSTRACT
AIM: To investigate possible abnormalities of serum potassium and calcium levels in patients with essential thrombocythaemia and significant thrombocytosis. METHODS: 24 cases of essential thrombocythaemia with significant thrombocytosis (platelet count > 700 x 10(9)/litre) had serum potassium and calcium estimations performed at the time of maximum thrombocytosis before treatment, and at the time of low platelet count after treatment with cytoreductive drugs. Selected patients were further investigated with plasma sampling and estimation of ionised calcium and parathyroid hormone. RESULTS: At the time of maximum thrombocytosis six patients had serum hyperkalaemia (> 5.5 mmol/litre) and five had serum hypercalcaemia (> 2.6 mmol/litre). Following treatment and reduction of the platelet count, hyperkalaemia resolved in all cases and hypercalcaemia in four of the five cases. Mean serum potassium and calcium concentrations were raised (p < 0.0001) at maximum thrombocytosis compared with the values when the platelet count was low. Serum potassium and calcium values were significantly correlated at all stages. Measurements on plasma consistently corrected the hyperkalaemia but not the hypercalcaemia. Serum hypercalcaemia was associated with raised ionised calcium and normal parathyroid hormone concentrations. CONCLUSIONS: Essential thrombocythaemia with significant thrombocytosis is associated with serum hyperkalaemia and hypercalcaemia. The probable mechanism of hypercalcaemia is the secretion of calcium in vitro from an excessive number of abnormally activated platelets. It is thus likely that the hypercalcaemia is an artefact, as is the hyperkalaemia.
Subject(s)
Artifacts , Hypercalcemia/etiology , Hyperkalemia/etiology , Thrombocythemia, Essential/complications , Adolescent , Adult , Aged , Aged, 80 and over , Female , Humans , Male , Middle Aged , Platelet Count , Thrombocythemia, Essential/blood , Thrombocytosis/complicationsABSTRACT
Exercise and diet are the cornerstones of management of non-insulin-dependent diabetes mellitus (NIDDM). Many older people have difficulty in exercising, missing benefits on glycaemic control, weight, cardiac disease and mood. We report the outcomes of a 6 month structured exercise and support programme based on a health promotion model, on physical activity, glycaemic control and parameters of cardiovascular risk in non-exercisers, compared with standard outpatient clinic education. A total of 26 non-exercising patients were randomised to an intervention or control group (ten men, 16 women; mean age (+/- S.D.) 60 +/- 8 years). Programme participation was not associated with any significant increase in activity. Glycated hemoglobin (HbAtc) levels tended to stabilise in the intervention group during the 6 month programme and to deteriorate in the control group (P = 0.03); by 12 months HbA1C levels deteriorated to a similar level in both. Programme participation did not cause significant change in anthropometric or metabolic parameters. Examining the cohort as a whole, increased activity over 6 months was associated with improvements in weight, body mass index (BMI), body fat and fasting insulin. Activity increases over 12 months were associated with improvements in weight and BMI. These changes could not be attributed to changes in energy intake or dietary composition. We conclude that while exercise can benefit older people with NIDDM, a programme based on a model of health promotion was not effective in increasing physical activity.
Subject(s)
Diabetes Mellitus, Type 2/therapy , Exercise , Health Promotion , Body Mass Index , Body Weight , Cohort Studies , Diabetes Mellitus, Type 2/physiopathology , Diabetes Mellitus, Type 2/psychology , Diet, Diabetic , Female , Glycated Hemoglobin/analysis , Humans , Hypoglycemic Agents/therapeutic use , Life Style , Male , Middle Aged , Social Support , Surveys and Questionnaires , Time FactorsABSTRACT
OBJECTIVES: To identify patients with discrepantly high clinic blood glucose concentrations compared with self reported values and to assess whether such patients have errors in self monitoring technique. To determine whether, in patients with good technique, the discrepancy is a transient phenomenon related to clinic attendance. DESIGN: Prospective study of diabetes clinic patients recruited over six months. SETTING: Outpatient diabetes clinic of a teaching hospital. SUBJECTS: 34 consecutive patients with non-insulin dependent diabetes who had had at least two consecutive clinic blood glucose concentrations more than 5 mmol/l higher than the mean self reported concentration. MAIN OUTCOME MEASURES: Assessment of monitoring technique; presence of cognitive or physical impairment; serum fructosamine concentration; home and clinic blood glucose concentrations. RESULTS: 15 of 34 patients had errors in monitoring technique, 12 of whom had cognitive or physical impairment. In the remaining 19, the mean (SD) blood glucose concentrations of capillary and venous samples taken at home (10.2 (0.6) and 12.2 (1.1) mmol/l respectively) were significantly lower than in those taken at the clinic (16.8 (1.6) mmol/l, p < 0.0002). The fructosamine concentration was significantly higher in patients with monitoring errors than those without (2.4 (0.4) v 1.8 (0.4) mmol/l, p < 0.0001). CONCLUSIONS: "White coat" hyperglycaemia was detected in about half the patients but errors in technique accounted for the rest of the discrepancies. Patients' ability should be assessed before teaching self monitoring and the technique checked regularly.
Subject(s)
Blood Glucose/analysis , Diabetes Mellitus, Type 2/blood , Hyperglycemia/etiology , Aged , Ambulatory Care , Aptitude , Blood Glucose Self-Monitoring , Fructosamine , Hexosamines/blood , Humans , Hyperglycemia/blood , Middle Aged , Observer Variation , Outpatient Clinics, Hospital , Prospective Studies , Random AllocationABSTRACT
A highly sensitive and quantitative assay for measuring protein in solution based on the capacity of protein to bind silver is described. In this procedure, protein samples are first treated with glutaraldehyde and then exposed to ammoniacal silver. After 10 min, the reaction is terminated by the addition of sodium thiosulfate and the optical density measured at 420 nm. The useful range of the assay for the majority of standard proteins tested lies between 15 and 2000 ng. This represents a 100-fold increase in sensitivity over the Coomassie brilliant blue dye-binding procedure. There is little or no interference from carbohydrates, nonionic detergents, or ethanol, and pretreatment of protein samples with Bio-Gel P-2 to remove salts, thiol agents, EDTA, and sodium dodecyl sulfate makes this procedure compatible with most commonly used buffers. The cost in terms of silver utilization is nominal with a typical assay involving 10 samples tested in triplicate amounting to less than $0.02 U. S.