Laboratory methods and quality assurance in the Cardiovascular Health Study.

The Cardiovascular Health Study is an observational cohort study of risk factors for cardiovascular disease in 5201 participants, ages > or = 65 years. We report the methods and quality-assurance results for blood procurement, processing, shipping, storage, and sample analysis used during the first examination period (May 1989-June 1990). The most frequent difficulty in phlebotomy and processing was the requirement of more than one venipuncture (in 2.6% of the participants). The CVs for control materials ranged from 0.93% for glucose to 10.7% for insulin; most were < 4%. In addition to standard quality-assurance methods, we applied two other methods: technical error calculation for replicates, and weighted linear regression to assess time trend in results of control materials. After outliers were excluded, technical error values ranged from 1.7 for uric acid to 18.8 for insulin. Factor VII and factor VIII had slight trends over the 12-month analysis period. Results of quality-assurance analyses used to resolve problems were successful, thereby improving the second laboratory examination.

Factor VII antigen levels in a healthy blood donor population.

We determined factor VII antigen (FVIIag) levels in 705 healthy blood donors ranging in age from 17 to 79 years using a two-site solid-phase enzyme immunoassay developed in our laboratory. The mean (+/- SD) FVIIag level for the total population was 102 +/- 31%. FVIIag levels for men (n = 375) and women (n = 330) were 101 +/- 28% and 103 +/- 33%, respectively. A significant increase in FVIIag was observed with age in both men (r = 0.25, p < 0.0001) and women (r = 0.35, p < 0.0001). FVIIag levels were significantly higher in women > 60 years when compared to men (median women: 125%; median men: 111%; p < 0.05). On a subset of the study group (n = 45), FVIIag levels were correlated to total cholesterol (r = 0.27, p = 0.08) and triglyceride (r = 0.41, p < 0.01). Assuming the commonly used reference interval of 60-140% for FVII, the frequencies of FVIIag values for < 60% and > 140% using our assay were 2.1% and 9.2%, respectively. Gender and age-related differences in FVIIag levels must be considered in a reference interval. We further suggest that assay-specific reference ranges be established, which may include values outside the commonly used values of 60-140%.

Stripping membranes at term: can it safely reduce the incidence of post-term pregnancies?

Membrane stripping has been used clinically for many years but has not been well studied. An investigation was undertaken to determine whether weekly membrane stripping beginning at 38 weeks could safely reduce post-term pregnancies. One hundred eighty patients with firm gestational dates were randomized to either a treatment or control group. Control subjects received a gentle cervicovaginal examination each week to assess Bishop scores, whereas the treatment group also underwent weekly stripping of membranes. Women who received treatment had earlier delivery (mean +/- SEM 8.60 +/- 0.74 versus 15.14 +/- 0.83 days; P less than .0001) and fewer post-term deliveries than those in the control group (three versus 14; P less than .004). The reduction of post-term pregnancies was most notable in nulliparous women with unfavorable Bishop scores. Complications were similar in both groups. Membrane stripping was safe and was associated with earlier delivery and a decreased incidence of post-term gestation.

Correlation of uterine activity using the Term Guard monitor versus standard external tocodynamometry compared with the intrauterine pressure catheter.

Uterine activity monitoring to detect preterm contractions and thus to manage patients in active labor is valuable to the clinician. Uterine activity measured by external devices using the guard ring principle or by standard tocodynamometers has been shown to be accurate concerning the frequency of uterine activity as compared with intrauterine pressure catheter-derived data in the third trimester. In this study, 26 women from 19-34 weeks in documented preterm labor had their uterine activity measured by a standard in-hospital monitor and a Term Guard tocodynamometer simultaneously. The standard monitor reflected 16-91% of the frequency of contractions noted by the Term Guard device, with a reduction in the correlation at gestational ages under 30 weeks. In another 20 patients between 17-36 weeks' gestation, these two methods of external tocodynamometry were compared with a transcervical catheter which measured actual intrauterine pressure and frequency of contractions. There was a good correlation between the Term Guard device and transcervically measured contractions (94.6%). At gestational ages of 28 weeks or less, there was poor performance from standard devices (less than 38% correlation with the intrauterine pressure catheter). These data have important implications for clinicians who monitor preterm patients on an ambulatory basis for early detection of preterm labor and also have clinical impact for the management of patients at early gestational ages in active labor.

A conserved epitope on several human vitamin K-dependent proteins. Location of the antigenic site and influence of metal ions on antibody binding.

A murine monoclonal antibody (designated H-11) produced by injecting mice with purified human protein C was found to bind several human vitamin K-dependent proteins. Using a solid-phase competitive radioimmunoassay with antibody immobilized onto microtiter plates, binding of 125I-labeled protein C to the antibody was inhibited by increasing amounts of protein C, prothrombin, and Factors X and VII over a concentration range of 1 X 10(-8) to 1 X 10(-6) M. Other vitamin K-dependent proteins including Factor IX and protein S did not inhibit or inhibited only at the highest concentration binding of radiolabeled protein C to the immobilized antibody. Chemical treatment of prothrombin with a variety of agents including denaturation by sodium dodecyl sulfate, reduction with mercaptoethanol followed by carboxymethylation with iodoacetic acid, citraconylation of lysine residues, removal of metal ion with EDTA, or heat decarboxylation did not destroy the antigenic site recognized by the antibody as measured by immunoblotting of prothrombin or prothrombin derivative immobilized onto nitrocellulose. Immunoblotting of purified vitamin K-dependent polypeptides with the monoclonal antibody following sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrophoretic transfer to nitrocellulose indicated that the antigenic site was found on the light chains of protein C and Factor X. Chymotrypsin digestion of prothrombin and isolation on QAE-Sephadex of the peptide representing amino-terminal residues 1-44 of prothrombin further localized the antigenic site recognized by the monoclonal antibody to the highly conserved gamma-carboxyglutamic acid-containing domain. The exact location of the antigenic determinant for antibody H-11 was established using synthetic peptides. Antibody H-11 bound specifically to synthetic peptides corresponding to residues 1-12 of Factor VII and 1-22 of protein C. Comparison of protein sequences of bovine and human vitamin K-dependent proteins suggests that the sequence Phe-Leu-Glu-Glu-Xaa-Arg/Lys is required for antibody binding. The glutamic acid residues in this peptide segment are the first 2 gamma-carboxyglutamic acid residues near the amino-terminal end in the native proteins. Increasing concentrations of Ca2+, Mg2+, or Mn2+ partially inhibited binding of 125I-protein C to the antibody in a solid-phase assay system with half-maximal binding observed at divalent metal ion concentrations of 2, 4, and 0.6 mM, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)

A monoclonal-antibody-based radioimmunoassay for measurement of protein C in plasma.

A monoclonal-antibody-based competitive radioimmunoassay for measuring human protein C is reported. With use of a purified protein C standard, the solid-phase assay was sensitive to less than 80 micrograms of protein C per liter. Intraassay CVs ranged from 5% to 8%; the inter-assay CV was 5.4%. Analytical recovery averaged 104% for purified protein C added to 10 samples of normal plasmas. The assay antibody could deplete plasma of all protein C, as determined by immunoaffinity chromatography followed by polyclonal Western blot analysis. Liquid-chromatographic gel permeation of plasma indicated a single immunoreactive species that had an appropriate molecular mass for monomeric protein C. Studies of monoclonal-antibody specificity showed no significant interferences by other vitamin K-dependent proteins. The mean protein C antigen concentration in plasma of 54 healthy subjects was 3.21 (SD 0.56) mg/L and was 1.51 (SD 0.52) mg/L for 22 patients on long-term warfarin therapy. Results of the monoclonal RIA correlated well with those by a polyclonal RIA also developed in our laboratory (r = 0.93) and an amidolytic functional assay (r = 0.88) for both normal plasma and plasma from patients on long-term warfarin therapy.

Transluminal balloon angioplasty in diabetic peripheral vascular disease.

Transluminal (balloon) angioplasty of iliac or superficial femoral stenoses in 18 diabetic patients resulted in a significant improvement in ankle/brachial systolic pressure index with marked symptomatic improvement in 16, little change in one and deterioration requiring arterial bypass surgery in one patient. Follow-up for 12 months or more showed that the initial good results were sustained despite a downward drift in ankle pressures. These findings indicate that transluminal angioplasty has a useful place in the management of proximal atherosclerotic stenotic lesions in diabetic patients with symptomatic peripheral vascular disease.