Clauss Method Research Articles

Comparison of Different Methods to Measure Fibrinogen Concentration in Canine Plasma with Respect to Their Sensitivity towards the Fibrinogen Degradation Products X, Y and D

In this study, fibrinogen measurements according to the Clauss method, photometric method and Jacobsson method have been investigated to find out how they are influenced by adding in vitro the purified canine fibrinogen degradation products (FDP) X, Y and D. Test results according to the Clauss method were found to be underestimated if the fragments X, Y and D were added while measurements according to the Jacobsson method turned out to underestimate the real fibrinogen concentration if the FDP Y and D were added. The Clauss method was particularly sensitive towards FDP. Results were considerably underestimated even with a quantity as little as 0.05 g FDP Y or FDP D/g fibrinogen (p < 0.05). The photometric method was only affected by FDP X leading to false high results. If FDP X was added, fibrinogen values were also overestimated with the Jacobsson method. Our results demonstrate that the photometric method is the most accurate.

Fibrinogen, angina and coronary heart disease in a Chinese population

Although fibrinogen is an established risk factor of coronary heart disease (CHD), whether fibrinogen is associated with CHD in Chinese is not clear. This population-based cross-sectional study aimed to analyse this relationship in Hong Kong Chinese. Fibrinogen was measured by the Clauss method in 1348 men and 1385 women aged 25–74 years. Severity of CHD was defined as most serious if the subjects had medically diagnosed CHD, as less serious if they had angina only, and as normal if they had neither. The prevalence of angina and CHD was respectively 2.4% and 2.2% in men and 3.2% and 2.7% in women. In men the age-adjusted mean fibrinogen concentration was 2.47 (95% confidence interval (CI) 2.43–2.51) g/l in the normal group, 2.65 (95% CI 2.45–2.85) g/l in the angina group, and 2.78 (95% CI 2.56–3.00) g/l in the CHD cases ( P<0.01); in women it was respectively 2.61 (95% CI 2.59–2.63), 2.66 (95% CI 2.50–2.82), 2.90 (95% CI 2.72–3.08) g/l ( P<0.01). The differences were significant after adjustment of other significant risk factors. We conclude that fibrinogen should be considered as a risk factor in Chinese.

The Effect of Atorvastatin on Serum Lipids, Lipoprotein(a) and Plasma Fibrinogen Levels in Primary Dyslipidaemia – A Pilot Study Involving Serial Sampling

SummaryWe conducted an open-label study to test the effects of atorvastatin on serum lipids, lipoprotein(a) [Lp(a)] and plasma fibrinogen levels. A total of 90 dyslipidaemic, nonsmoking patients (45 patients with primary hypercholesterolaemia and 45 patients with primary mixed hyperlipidaemia) aged 48 ± 11 years were studied. The patients were treated with 20 mg of atorvastatin for 24 weeks, in a single nocturnal dose. At baseline and every eight weeks, the fasting lipid profile, together with serum Lp(a) and plasma fibrinogen levels (Clauss method), were measured. Atorvastatin was highly effective in normalising the serum lipid profile. No significant change in median serum Lp(a) levels was observed in the whole group of patients (0.14 g/l before, vs. 0.16 g/l after, treatment) as well as in patients with raised (> 0.30 g/l) baseline levels (n = 32). A small non-significant increase of plasma fibrinogen was found (3.04 g/l vs. 3.14 g/l) after 24 weeks of atorvastatin administration. The effects of atorvastatin on both these variables did not differ in patients with hypercholesterolaemia or mixed hyperlipidaemia.In conclusion, our findings suggest that the effect of atorvastatin on plasma fibrinogen levels in dyslipidaemic patients without evident vascular disease is not clinically relevant. Furthermore, any rise in fibrinogen levels that may occur is likely to be transient in nature. Further studies are necessary to clarify this issue. There was no evidence that atorvastatin influences serum Lp(a) levels.

The relationship between fibrinogen and other coronary heart disease risk factors in a Chinese population

Few studies have examined fibrinogen in Chinese populations in which the incidence of coronary heart disease (CHD) is lower than that in the West. This study aimed to examine the relationship between fibrinogen and other CHD risk factors in Hong Kong Chinese. Fibrinogen was measured by the Clauss method in 1359 men and 1405 women aged 25–74 years, randomly selected from the Hong Kong population. Mean fibrinogen level increased with age, from 2.22 g/l in those aged 25–34 years to 2.76 g/l in 65–74 years in men, and from 2.42 to 2.94 g/l respectively in women. The most important factors associated with fibrinogen were age, obesity and blood lipid levels in both genders. In men, smoking was associated with higher fibrinogen levels and cessation of smoking with lower levels. Prospective studies are needed to examine the role of fibrinogen in CHD in Chinese and other Asian populations.

Prothrombin time derived fibrinogen determination on Sysmex CA-6000.

AIM: To evaluate PT derived fibrinogen determinations with reference to the Clauss fibrinogen assay using a Sysmex CA-6000 random access coagulation analyser. METHODS: Samples were analysed from normal subjects (n...

Measurement of plasma fibrinogen concentration by the prothrombin-time-derived method: applicability and limitations.

A prothrombin-time-derived method was used to measure plasma fibrinogen concentration (PFC) in 286 samples from 242 normal and 44 orally anticoagulated subjects. Absorbance changes at 405 nm (deltaOD) during the clotting process were obtained by an automatic coagulometer and their relationship with plasma fibrinogen concentration (range 90-1090 mg/dl), measured by the Clauss method, was investigated. A weighted linear regression between the deltaOD and the Clauss-derived PFC values provided the best fit of the experimental data. The fitting equation was found to be reliable and accurate for PFC determination in normal subjects, whereas a systematic overestimate of fibrinogen level was demonstrated in plasma with high fibrinogen concentrations (> 400 mg/dl) and in plasma from anticoagulated patients. The systematic overestimate in the latter samples could be a result of an increased fibrin gel turbidity, as shown by in-vitro experiments using purified fibrinogen clotted by different thrombin concentrations. The PFC overestimate by the prothrombin-time-derived method could also be experimentally reproduced by competitively inhibiting thrombin-fibrinogen interaction by hirudin 54-65 peptide and the fibrinogen fragment E. A similar qualitative result was also found for the prothrombin-time-derived method in the presence of the Gly-Pro-Arg-Pro peptide, which competitively inhibits the end-to-end fibrin aggregation process. Notably, under both the above experimental conditions, the Clauss method underestimated the PFC. On the other hand, the 'clot recovery' method was minimally affected by the above inhibitors. These results indicate that the prothrombin-time-derived method is accurate and precise for most routine purposes. Its precision seems inadequate, however, under those conditions where the prothrombin time is prolonged (such as anticoagulant therapy) and in the presence of high fibrinogen levels.

Effects of Tourniquet Technique, Order of Draw, and Sample Storage on Plasma Fibrinogen

The use of plasma fibrinogen concentrations to predict clinical ischemic events in subjects with and without prior evidence of atherosclerosis (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14) has led to recommendations to incorporate fibrinogen into the cardiovascular risk profile (15). Such use of plasma fibrinogen requires careful attention to potential sources of variability, as only small (5%) absolute differences in fibrinogen distinguish subjects who develop cardiovascular disease from those subjects who do not (16). Variability in fibrinogen results apart from intraindividual differences is difficult to quantify, because the few groups who have examined these issues used different assays for fibrinogen determination. Moreover, the functional assay for fibrinogen is highly influenced by technician expertise and manipulation (17). Previously, we examined within-run analytical CV, within-person, within-day biological variation, and a 6-week within-person biological variation with the Clauss method for fibrinogen determination (16). We describe here selected effects of sample collection and storage on fibrinogen results and we propose guidelines for sample collection and storage. Blood was collected in evacuated tubes (5-mL capacity) containing 0.5 mL of 0.129 mol/L (3.8%) buffered citrate solution (Becton Dickinson). Fibrinogen concentrations were determined by thrombin clottable time with the Clauss method (Dade Data-Fi, Baxter Diagnostics) (18) with bovine thrombin (100 kU/L) and 2.8 × 10−2 mol/L sodium barbital in 0.125 mol/L sodium chloride. Duplicate plasma samples were diluted 1:10 (by vol) with an imidazole buffer (Organon Teknika) and measured at 20- and 40-s intervals at 37 °C in a fibrometer (Model BBL, Becton Dickinson). All samples were acquired from healthy, nonsmoking volunteers who were seated ≥5 min before phlebotomy (19). Volunteers were excluded if they had current illnesses, regular …

Physical activity, physical fitness, blood pressure, and fibrinogen in the Northern Ireland health and activity survey.

To investigate the relationship between physical activity, physical fitness, blood pressure, and fibrinogen. This was a cross sectional population study using a two stage probability sample. Northern Ireland. A sample of 1600 subjects aged 16-74 years from the population of Northern Ireland. Physical activity profile from computer assisted interview using the Allied Dunbar national fitness survey scales. Physical fitness using estimation of VO2 max by extrapolation from submaximal oxygen uptake while walking on a motor driven treadmill. Systolic and diastolic blood pressure measured with a Hawksley random zero sphygmomanometer. Measurement of fibrinogen using the Clauss method. There were significant relationships between both current and past activity and blood pressure. These were of a magnitude that would have been clinically significant, but for the fact that, with the exception of the relationship between habitual activity and diastolic pressure (p = 0.03) and past activity and systolic pressure (p = 0.03) in men, they were not sustained after adjustment for the effect of age using analysis of variance. After adjustment for other potentially confounding factors using multiple regression, there was an inverse relationship between systolic blood pressure and past activity in men, so that those with a life-time of participation compared with a life-time of inactivity had a lower systolic blood pressure of 6 mmHg (p < 0.05). There was a highly significant (p < 0.001) inverse association between both systolic and diastolic blood pressure and physical fitness (VO2 max) which was not sustained after adjustment for possible confounding factors. There were relationships between fibrinogen and highest recorded activity (p < 0.001), habitual activity (p < 0.01), and past activity (p < 0.01) in men but no significant relationship in women. The relationship between fibrinogen and activity was no longer sustained after adjustment for possible confounding factors. There was a highly significant (p < 0.001) inverse relationship with physical fitness using VO2 max. This relationship was sustained after adjustment for possible confounding factors in both men (p < 0.05) and women (p < 0.001). There was a relationship between physical activity, physical fitness, and blood pressure but the relationship was greatly influenced by age. A reduction of 6 mmHg in systolic blood pressure associated with past activity is of clinical significance and supports the hypothesis that physical activity is of benefit in reducing cardiovascular risk. There was a lower level of fibrinogen in those who were most active but this relationship was not significant after adjustment for possible confounding factors. There was also a lower level of fibrinogen those who were most fit (VO2 max) and this relationship persisted even after adjustment for possible confounding factors.

127. Levels of functional versus intact fibrinogen in 140 patients with acute myocardial infarction treated with Reteplase

Reteplase, the novel K2P-deletion mutant of t-PA, was administered in a dose-finding multicenter study (GRECO) to 140 patients (pts) with acute myocardial infarction (AMI). 40 pts (group A) received an 18 mg (10 Megaunits (MU)) i.V. single bolus of Reteplase and 100 subsequent pts (Group B) were treated with a 27 mg (15 MU) i.v. single bolus. Fibrinogen (fbg) was measured using two different methods before (pre) and 2, 4, 8 and 24 h after Reteplase: the first fbg method was a clotting rate assay according to the Clauss method (functional fbg), the second an enzyme immunoassay (EAI) for immunologically intact fbg. In 10 out of the group B pts (group C; 27 mg) changes of fbg levels were measured in very close intervals until 18 days (dl8) after thrombolysis. Results: The levels of functional (Clauss) and intact (EIA) fbg differed significantly at each time point: A (Clauss/EIA; median values; [g/1]): Pre: 2.8/3.5; 2 h: 1.7/2.7 (60%/77% of the pre-bolus value of each method); 4 h: 1.7/2.7 (62%/76%); 8 h: 1.5/2.6 (54%/74%); 24 h: 2.2/3.0 (79%/86%) (p<0.001 between Clauss and EIA at any time of sampling). B: Pre: 2.6/3.2; 2 h: 1.0/2.1 (37%/66%); 4 h: 0.9/2.2 (36%/69%); 8 h: 1.0/2.2 (37%/69%); 24 h: 1.6/2.4 (63%/75%) (p<0.0005). C: Pre: 2.7/3.1; 30 min.: 1.6/2.5; 60 min.: 1.3/2.4; 2 h: 1.2/2.3; 4 h: 1.2/2.2 (44%/69%); 8 h: 1.3/2.2; 24 h: 1.8/2.5; 48 h: 2.8/2.7; 72 h: 4.1/3.6; d6: 4.7/3.8 (173%/123%); d9: 4.5/3.9 (167%/126%); d!2: 4.1/3.5; d!5: 3.9/3.2; d!8: 4.0/3.4 (p<0.05; exception: 48 h: not significant). Conclusions: The levels of functional (Clauss) fbg showed lower nadirs and higher rebound levels (C) compared to the intact (EAI) fbg levels. Lower nadirs measured by the Clauss method might reflect the disturbance of this method by fibrin(ogen) degradation products. Higher rebound levels of functional fbg (Clauss) might indicate newly synthesized fast clotting HMW (high molecular weight) fbg and therefore a risk factor for reocclusions in AMI pts treated with thrombolytic agents. In contrast to our previous studies in rt-PAtreated AMI pts, the pretreatment ratio of functional (Clauss) to intact (EAI) fbg here was <0.9 in groups A, B and C compared to 1.6 in the rt-PA study. © Pearson Professional Ltd 1996.

The influence of Helicobacter pylori status on circulating levels of the coagulation factors fibrinogen, von Willebrand factor, factor VII, and factor VIII.

Helicobacter pylori (H. pylori) infection has been associated with an increased risk of developing ischemic heart disease (IHD). It has been suggested that a persisting low-grade acute phase response results from the chronic inflammation caused by H. pylori infection, which may give rise to increased circulating levels of certain coagulation factors. One hundred three (53 male) nonconsecutive, randomly selected white subjects with symptoms of dyspepsia were recruited for study from an outpatient endoscopy clinic at Leeds General Infirmary. The presence of H. pylori was determined by histological and microbiological investigation, a rapid urease test, and a 13carbon urea breath test (13C-UBT). Fibrinogen was measured by the Clauss method, factor VIII:C (FVIII:C) and factor VII:C (FVII:C) were measured by clotting rate assays, and the von Willebrand factor (vWF) was determined by an enzyme-linked immunosorbent assay. No difference was found in levels of coagulation factors according to H. pylori status. Multiple regression models were used to account for the effect of covariates and H. pylori status on levels of FVII:C, FVIII:C, vWF, and fibrinogen, and again H. pylori status was not a significant determinant of levels of any of these coagulation factors. No difference occurred in full blood count, platelet count, white cell count, or plasma viscosity in individuals who were H. pylori-positive compared with those who were negative. H. pylori infection is not associated with increased circulating levels of fibrinogen, FVII:C, vWF.Ag, or FVIII:C or hemorrheology in this patient group.

The role of hemorheological factors in hypertensne retinopathy

Hemorheological factors play an important role in the pathogenesis of different cardiovascular diseases. In the present study the fundus appearance and hemorheological parameters (plasma and whole blood viscosity *WBV* by capillary viscosimetry; fibrinogen level by the Clauss method) of 33 hypertensive patients (23 females, 10 males; mean age: 55 years) were examined. The fundus appearance showed retinopathy in all the cases between stages I-III. All the measured hemorheological parameters of the examined patients were in the pathological range (WBV at 90 lis: 5.18 mPas) and were significantly (p < 0.01) higher than in healthy controls (WBV at 90 lis: 4.18 mPas). The hemorheological factors showed a parallel deterioration with the fundus appearance, namely their values were significantly (p < 0.01) higher in patients with a fundus appearance stage III (WBVat 90 lis: 6.02 mPas) than stage I (WBVat 90 lis: 4.51 mPas). Our results show that there is a correlation between hemorheological parameters and fundus appearance in hypertensives, and this suggests that hemorheological factors may playa role in the development of hypertensive retinopathy.

Assessment of Relative Contributions of Fibrinolysis and Fibrinogenolysis to the Abnormalities of Plasma Fibrinogen/Fibrin-Retated D and E Antigens and Their Ratio in Liver Cirrhosis

Many pathogenic mechanisms play a part in hemorrhage in chronic liver disease. This study was done to characterize the alterations of fibrinogen components and dysfibrinogenemia in patients with liver cirrhosis. Plasma from 31 patients with liver cirrhosis was analyzed to determine the fibrinogen/fibrin-related D and E antigens by latex photometric immunoassay; fibrinogen by the Clauss method; fibrinogen degradation product (FgDP), protein C antigen, and tissue plasminogen activator (tPA) by enzyme immunoassay; and antithrombin III by the colorimetric method, respectively. Reptilase, time and fibrin monomer (FM) tests were also done. Fibrinogen/fibrin-related D and E antigens were higher and their ratio (D/E) was lower in liver cirrhosis compared with normal subjects. Fibrinogen levels were inversely correlated with D (p = 0.0001) and E (p = 0.0001) antigenic levels in plasma. FgDP levels were not significantly correlated with D and E levels. However, semiquantitative D-dimer levels had significant association with D and E levels. Reptilase time was abnormally prolonged in all patients with high D and E levels, and FM tests were also positive in most patients with increased levels of D and E. Protein C antigen levels were inversely correlated with D (p = 0.0110) and E (p = 0.0112) concentrations but were well correlated with clottable fibrinogen concentrations (p = 0.0058). Hypercoagulability followed by pathologic activation of fibrinolysis, rather than synthesis of abnormal fibrinogen molecules, may contribute to hemorrhage. Not only true hypofibrinogenemia due to the decreased synthesis of intact fibrinogen but also elevated levels of these antigens may be clinically significant in the treatment of cirrhotic patients at risk of bleeding. Protein C may play an important regulatory role in fibrinolysis.

Measuring plasma fibrinogen levels in patients with liver cirrhosis. The occurrence of proteolytic fibrin(ogen) degradation products and their influence on several fibrinogen assays

In patients with liver cirrhosis the fibrinogen molecule is under constant attack of various proteolytic enzymes, which might affect results of the different assay systems for fibrinogen. We therefore studied the measurement of fibrinogen in the plasma of patients with mild, moderate and severe cirrhosis of the liver. Fibrinogen levels were measured with the Clauss method (functional fibrinogen); an enzyme immuno assay (EIA) for HMW + LMW fibrinogen; and an assay that measures the total clottable fibrinogen. With all three methods we found normal or slightly increased fibrinogen levels in patients with mild or moderate cirrhosis, whereas patients with severe cirrhosis had decreased levels. No evidence was found for increased partial fibrinogen proteolysis, resulting in increases of LMW'-fibrinogen in cirrhotic patients. We further observed that fibrinogen degradation products levels increased slightly with the severity of the disease, but were still in the normal range in patients with severe cirrhosis. This indicates a very low level of primary fibrinolysis. Fibrin degradation products levels increased much stronger, which points to intravascular coagulation. The levels of the fibrin degradation products remained below the level where they are expected to influence the Clauss assay. In patients with liver cirrhosis the measurement of plasma fibrinogen levels with the three studied methods give comparable results. We suggest to apply the Clauss assay in cirrhotic patients because of this and because it has a good reproducibility and because the test is cheap, quick and easy to perform.

998-121 Effect of Hormone Replacement Therapy on Fibrinogen Level in Postmenopausal Women in the Framingham Offspring Study

Hormone replacement therapy (HRT) is associated with a decreased risk of coronary heart disease (CHD) in postmenopausal women, but the mechanism of its protective effect is not fully characterized. To evaluate the relation ship between postmenopausal HRT and fibrinogen, an established hemostatic risk factor for CHD, we measured fibrinogen using the Clauss method in 858 women free of CHD in cycle 4 of the Framingham Offspring Study. The table shows mean ± SD fibrinogen levels for pre and postmeonopausal women according to use of HRT N Fibrinogen (mg/dl) %Δ p-value Premenopause 303 289 ± 53 Postmenopause (No HRT) 383 313 ± 58 ↑7.7% * &lt; 0.001 * Postmenopause (HRT) 86 284 ± 44 ↓9.3% ** &lt; 0.001 ** * Premenopause vs. Postmenopause (No HRT); ** Postmenopause (No HRT) vs. Postmenopause (HRT) (Age adjusted) These differences persisted upon multivariate adjustment for smoking, use of antihypertensive medication, diabetes mellitus, body mass index, alcohol intake, total cholesterol and HDL cholesterol. Postmenopausal HRT is associated with fibrinogen levels that are comparable to those found in premenopausal women. These data suggest that the protective effect of postmenopausal HRT may be mediated in part by favorable alterations in the hemostatic system.

Screening of dysfibrinogenaemia using the fibrinogen function versus antigen concentration ratio

The diagnosis of inherited and acquired dysfibrinogenaemia is usually suspected in patients with otherwise unexplained prolonged thrombin time or other tests with thrombin-like enzymes (1). Confirmation of the diagnosis requires discordant results from the investigation of functional fibrinogen and its antigen concentration. However, the issue of the difference between the two results required to confirm dysfibrinogenaemia has rarely been addressed. A difference of at least 0.5 g/l between functional fibrinogen using the method of Clauss and heat precipitation method according to Schulz has been suggested as a prerequisite (1). In the case of acquired dysfibrinogenaemia with an underlying liver disease the discordance should reach at least 1.0 g/l (2). Rodgers and Garr (3) suggested to establish a ratio between fibrinogen function and antigen concentration. In that study plasma from healthy blood donors was investigated using the Clauss method and radial immunodiffusion. We applied this approach to randomly selected patients at the time of admission to a University Hospital Department. Since fibrinogen is one of the major acute phase proteins, the determination of the C-reactive protein (CRP) was included for comparison.

Intraindividual variability of fibrinogen levels and cardiovascular risk profile.

Prospective population studies have established that fibrinogen is an independent predictor for ischemic heart disease and stroke. These study conclusions have prompted recommendations that fibrinogen determinations be included in the cardiovascular risk profile. The routine availability of fibrinogen measurements may result in widespread screening prior to establishing the validity of a single fibrinogen level as an accurate descriptor for individual subjects. The objectives of this study were to describe the methodological and intraindividual components of variability in fibrinogen measurements determined by using the Clauss method; to establish the usefulness of a single fibrinogen measurement on risk stratification and retest reproducibility; and to determine the influence of intraindividual fibrinogen variability on sample size estimates. Fibrinogen levels were measured by a modification of the Clauss method. Three cohorts of apparently healthy, nonsmoking volunteers were recruited. The single-day intra-individual component of fibrinogen variability was determined in 39 subjects. For the 5-day intraindividual component of fibrinogen variability, 32 subjects were recruited, and in the 6-week intraindividual study, 28 subjects were included. The coefficient of variation for the methodological component of fibrinogen variability was 5.8% as determined from batch analyses, but the intraindividual coefficient of variation for replicate measures on a single day was 10.7%. The 5-day intraindividual coefficient of variation was 14.2%, and for the 6-week period it was 17.8%. Based on the 6-week data, an average of four fibrinogen measures is required to reduce misclassification error to less than 10%. Sample size estimates were made based on predetermined levels of statistical power and the 6-week intraindividual and interindividual variability estimates.(ABSTRACT TRUNCATED AT 250 WORDS)

Results of a collaborative study for fibrinogen measurement. Evidence that the use of a common calibrator improves interlaboratory agreement

One hundred and sixty-five laboratories were asked in two different surveys to perform duplicate fibrinogen measurements on the same lyophilized plasmas by their own methods and reagents and two different methods of calibration. The between-laboratory variability, expressed as coefficient of variation (CV), and the extent of between-method and between-reagent differences were taken as a measure of agreement between measurements. It was found that the overall between-laboratory range of CV values was 9-16% and that it could be improved if a common calibrator was used. The improvement was more pronounced for the thrombin time-derived (Clauss) method (average CV reduction 43%) than for the prothrombin time (PT)-derived method (average CV reduction 12%). A satisfactory agreement was found between the PT-derived and the Clauss method for the normal-PT plasma, whereas the PT-derived was slightly higher than the Clauss method for the abnormal-PT plasmas, irrespective of calibration. There were statistically significant between-reagent differences within the Clauss method, which were reduced if the common calibrator was used. In conclusion, the results shows that a system of common calibration for fibrinogen determination improves interlaboratory agreement by reducing the CV and minimizing between-reagent differences, particularly for the Clauss method. The authors recommend manufacturers of reagents to link their calibrators to the International Standard for fibrinogen.

Messung der Fibrinogenkonzentration beim gesunden Hund: Standardisierung, Methodenvergleich und Referenzwerte

Plasma fibrinogen concentration was measured in 67 healthy, adult dogs using five different methods (gravimetry, methods described by JACOBSSON (1955) RATNOFF and MENZIE (1951), and CLAUSS (1957), and functional photometric assay). Apart from using linear regression and the Pearson correlation coefficient (r) in order to characterize the relation between different methods, reference ranges (2.5-97.5%-fractile) were calculated for all methods. For calibration of the CLAUSS method (1957) and the photometric assay, dog plasma with a defined fibrinogen concentration was used. Measurements of commercial human fibrinogen standards yielded a good conformity with the concentrations specified by the manufacturer (values approximately 3% too low). These standards appear, therefore, to be also suited to the calibration of measurements of dog fibrinogen. The reference range for the gravimetry was 1.08-2.88 g fibrinogen per litre of plasma. A considerable conformity and close correlation was seen between the fibrinogen concentration measured by gravimetry and by using methods described by JACOBSSON (1955; y = 1.088 x -0.142, r = 0.967) or CLAUSS (1957; y = 0.999 x -0.004, r = 0.973), respectively. Between the reference-method gravimetry and the photometric method and RATNOFF-MENZIE (1951) method, respectively, a less close correlation, as well as a minor conformity, was found.

Prothrombin time (pt)-derived fibrinogen assay: three different commercial systems compared with the clauss method: [formula omitted], A. Tripodi, M. Maccaferri, C. Manotti, G. Palareti, F. Rodeghiero, M. Ruggeri, P.M. Mannucci. On behalf of the CISMEL Hemostasis Subcommittee (Comitato Italiano per la Standardizzazione dei Metodi in Ematologia e Laboratorio)

Prothrombin time (pt)-derived fibrinogen assay: three different commercial systems compared with the clauss method: [formula omitted], A. Tripodi, M. Maccaferri, C. Manotti, G. Palareti, F. Rodeghiero, M. Ruggeri, P.M. Mannucci. On behalf of the CISMEL Hemostasis Subcommittee (Comitato Italiano per la Standardizzazione dei Metodi in Ematologia e Laboratorio)

A viscometric method of measuring plasma fibrinogen concentrations.

A technique based on deducing the viscosity of serum from that of plasma was compared with the commonly used Clauss method. The two methods correlated closely (r = 0.914). The reproducibility of the viscometric method was slightly poorer than the Clauss technique at low fibrinogen concentrations, equal to that at medium fibrinogen concentrations, and marginally better at high concentrations. Fibrinogen can therefore be measured reasonably accurately with the viscometric method, and can be recommended as an alternative for laboratories possessing a viscometer.