Almost precisely a century ago, in the 1920s and 1930s, cattle bled to death in North America after being fed moldy hay containing sweet clover, the yellow Melilotus officinalis, and the white Melilotus albus. The toxic substance in the hay inhibiting blood coagulation was identified and named dicumarol. Further development resulted in warfarin, an oral anticoagulant that has been used for over 70 years and still is, even though newer direct-acting oral anticoagulants (DOACs) are mainly replacing it. For some patients, warfarin is still the drug of choice. A safe warfarin treatment needs repeated blood sample analysis (PT-INR), and with the new DOACs come new laboratory challenges. The aim of this thesis was to investigate ways laboratory methods can contribute to improving oral anticoagulant treatment. 

Paper I explores genetic variants of the enzyme targeted by warfarin, VKORC1. The result shows that the haplotype VKORC1*2 is the most important of the VKORC1 haplotypes for warfarin dosage, with a lower dose requirement. The VKORC1*2 haplotype was also related to more unstable PT-INR levels. 

Paper II describes a cross-section study comparing warfarin treatment control, as PT-INRs within the intended therapeutic range, in primary health care centers (PHCCs) and specialized anticoagulation clinics (ACCs). Both settings showed good therapeutic control, with at least as good therapeutic control in the PHCCs as in the ACCs. Today, almost all warfarin treatment in our region is centralized to ACCs. 

Paper III focuses on the modification of a point-of-care PT method. A ratio of PT from two different dilutions of each patient sample was calculated and used as an indirect measure of DOAC activity. There were close correlations between the PT ratio and drug concentrations measured at the hospital laboratory. The detection level varies between DOACs and may limit its use in some situations. 

Paper IV evaluated the MRX PT DOAC, an assay based on the PT ratio principle. It was found to be able to detect potentially interfering DOAC levels in plasma samples. Confirmatory testing is recommended, as is sensitivity improvement for the detection of specific interferences.   

För nästan exakt 100 år sedan dog boskap i Nordamerika av stora blödningar. Det skulle visa sig att det berodde på att de utfodrats med mögligt hö innehållande gul och vit sötväppling, Melilotus officinalis och Melilotus albus. Den giftiga substans som bildas hindrar blodet från att koagulera. Forskare lyckades identifiera och renframställa substansen, och en vidareutveckling av den gav upphov till warfarin, ett “blodförtunnande” läkemedel (antikoagulantia) i tablettform. Warfarin används än idag, även om nya antikoagulantialäkemedel används allt oftare. För vissa patienter är warfarin ännu det bästa läkemedlet. Warfarinbehandlade patienter kontrolleras regelbundet med analys PK-prov på laboratorium för att behandlingen ska vara säker, och med de nya läkemedlen kommer nya analysutmaningar. Målsättningen med den här avhandlingen har varit att undersöka olika sätt som laboratoriemetoder kan bidra till att förbättra antikoagulantiabehandling.

I delarbete I har vi sett att det finns en koppling mellan vissa genetiska varianter och ett lägre behov av warfarin, och likaså en mer svårinställd behandling.

I delarbete II undersökte vi kvaliteten på warfarinbehandlingen i primärvård jämfört med specialiserade antikoagulantia(AK-)mottagningar genom jämförelse av hur PK-proven under en viss vecka förhöll sig till önskade värden. Båda vårdformerna visade god kvalitet på warfarinbehandlingen, minst lika bra i primärvården som på AK-mottagningarna. Sedan studien gjordes har nästan all warfarinbehandling centraliserats till AK-mottagningar.

I delarbete III modifierade vi en analysmetod som vanligen används för analys av PK-prov, med sikte på att också kunna använda den för analys av effekt av de nya antikoagulantialäkemedlen. Vi såg en god överensstämmelse mellan den modifierade metodens resultat och ordinarie analys.

I delarbete IV utvärderade vi MRX PT DOAC, en analysmetod som bygger på den princip som beskrivs i delarbete III. Vi använde MRX PT DOAC för att upptäcka prover med läkemedel som kan störa andra analyser. Vi såg goda resultat men också förbättringspotential.  

Background

Oral anticoagulant therapy is used to prevent thrombosis in patients with atrial fibrillation (AF), venous thrombosis and prosthetic heart valves. The introduction of new therapies emphasizes the need to discern the best practice for the patients remaining on warfarin treatment. This study compares patient characteristics and therapeutic control in two settings managing warfarin treatment: Swedish primary health care centers (PHCC) and specialized anticoagulation clinics (ACC).

Methods

Prothrombin time (PT) test results reported as International Normalized Ratio (INR) were collected for five consecutive days from patients on warfarin treatment; 564 PHCC and 927 ACC patients. Therapeutic control was calculated as PT test results in relation to intended therapeutic range (TR). Mann–Whitney Rank Sum Test and Chi² test were used for statistical comparisons.

Results

The PHCC patients were older than the ACC patients, 76 v. 70 years (p<0.01) with a predominance of men in both groups. The reasons for treating differed between the groups. Seventy-two percent of PHCC patients and 66% of ACC patients had a PT-INR within the intended TR (p<0.05). Men generally had better results than women (72% v. 63%, p<0.001) and particularly in the PHCC group v. the ACC group (78% v. 69%, p<0.01).

PT-INR above intended TR was significantly more common in the ACC setting, (p<0.05), for women overall (p<0.01), for women in the PHCC setting, and for ACC men (p<0.05).

Conclusions

In this study both settings achieved good therapeutic control of warfarin treatment with a minor advantage for PHCC over ACC, and better results for men, especially in the PHCC setting. As patient characteristics differ between the PHCC and ACC, it is important to conduct further randomized studies to discern the best practice locally for warfarin management also after the introduction of new drugs.

Background: Vitamin K epoxide reductase (VKORC1) is the site of inhibition by coumarins. Several reports have shown that mutations in the gene encoding VKORC1 affect the sensitivity of the enzyme for warfarin. Recently, three main haplotypes of VKORC1; *2, *3 and *4 have been observed, that explain most of the genetic variability in warfarin dose among Caucasians.

Objectives: We have investigated the main haplotypes of the VKORC1 gene in a Swedish population. Additional objective was to screen the studied population for mutations in the coding region of VKORC1 gene.

Patients/methods: Warfarin doses and plasma S- and R-warfarin of 98 patients [with a target International Normalized Ratio (INR) of 2.0–3.0] have been correlated to VKORC1 haplotypes. Controls of 180 healthy individuals have also been haplotyped. Furthermore, a retrospective analysis of case records was performed to find any evidence indicating influence of VKORC1 haplotypes on warfarin response in the first 4 weeks (initiation phase) and the latest 12 months of warfarin treatment.

Results and conclusions: Our result shows that VKORC1*2 is the most important haplotype for warfarin dosage. Patients with VKORC1*2 haplotype had more frequent visits than patients with VKORC1*3 or *4 haplotypes, higher coefficient of variation (CV) of prothrombin time-INR and higher percentage of INR values outside the therapeutic interval (i.e. 2.0–3.0) than patients with VKORC1*3 or *4 haplotypes. Also, there was a statistically significant difference in warfarin dose (P < 0.001) and R-warfarin plasma levels (P < 0.01) between VKORC1*2 and VKORC1*3 or 4 haplotypes. Patients with VKORC1*2 haplotype seem to require much lower warfarin doses than other patients.

Warfarin is the most common agent used for control and prevention of venous as well as arterial thromboembolism. Although warfarin is administered as a racemic mixture of two stereoisomers (S and R), the S-form is mainly responsible for the anticoagulant effect. The anticoagulant effect of the drug is monitored by analysis of prothrombin complex (International Normalised Ratio,INR). In some cases, however, the measurements of plasma warfarin concentration are needed. Here, we present a new, rapid, sensitive and cost-effective HPLC-method for the determination of warfarin enantiomers in plasma. The chromatographic system consisted of Waters 616 gradient pump, Waters 996 photo diode array detector, Gilson 230 autoinjector and Pirkle (R,R) Whelk-O1 column (25 cm × 4.6 mm I.D., 5 μm). An isocratic mobile phase of methanol/acetonitrile/water (50/10/40, v/v) with 0.1% glacial acetic acid was used. The follow rate was 1 mL/min. Data analysis was carried out with Waters Millennium³². The absorbance at 305 nm was measured with a total run-time of 15 min. Method linearity was studied by establishing regression data containing eight points over the range 0.08–10 μg/mL. In this range, warfarin showed to be linear (r² = 0.9997 for S-warfarin and r² = 0.9998 for R-warfarin). The limit of detection in plasma was 16 ng/mL for S-warfarin and 18 ng/mL for R-warfarin. Limit of quatitation was defined as 10 × LOD. The extraction recovery was approximately 80%. Also the relation between INR and warfarin concentration was investigated. As expected, there was a low correlation between these two variables (r = 0.23, y = 0.3044x + 0.9712). This method offers a rapid and cost-effective determination of warfarin enantiomers in human plasma.

Measuring cortisol in saliva offers important advantages compared to measurement in plasma or serum. However, the sampling procedure and also the detection limit cause problems, especially in paediatric and neonatal care. We describe a simple and efficient sampling procedure, together with a modification of a radioimmunoassay, which enables analysis of low (down to 1 nmol/L) concentrations of salivary cortisol (10 times lower detection limit than in the original procedure). This setting was used in studying salivary cortisol concentrations before and after heelstick on healthy newborn infants. A significant rise (median 81%, p <0.01) in salivary cortisol as response to this invasive stressor was noted.

Background/Aim: It is known that spontaneous prolonged prothrombin time-international normalized ratio may be caused by deficiency of factor VII (FVII). The activity of FVII in the presence of thromboplastins of different origin is affected by the presence of specific mutations in the F7 gene. The present study aims to evaluate patients with mild FVII deficiency and somewhat discrepant FVII activity depending on the use of human or rabbit thromboplastin in relation to mutations in the FVII gene and markers of thrombin generation.

Patients and methods: A cohort of 10 patients with mild deficiency of FVII and discrepant FVII activity was investigated. The median ratio of the FVII activity in the presence of human/rabbit thromboplastin was 1.4. All but 1 patient had mild to no bleeding symptoms. A genetic analysis of the F7 gene was performed. Thrombin generation was measured by the calibrated automated thrombogram in platelet poor plasma in the presence of human recombinant and different dilutions of rabbit thromboplastin and compared with thrombin generation in healthy controls (n=12). Thrombin generation was measured in 9 patients as 1 was treated with warfarin at the time of the blood sampling.

Results: Six previously described mutations were found. Two of those (FVII Padua and FVII Shinjo) are known to affect the results for FVII activity dependent on the species origin of the thromboplastin. Nine out of 10 patients had one mutation in common (Arg353Gln), which however does not affect the binding site of FVII to tissue factor. Lagtime and ttpeak increased with decreasing concentrations of thromboplastin and total and maximum thrombin concentrations increased with increasing thromboplastin concentrations in the patients with FVII deficiency. ETP in patients with FVII deficiency was 86% of ETP in controls.

Discussion: The Arg353Gln mutation was very common, however it does not appear to affect the reactivity towards thromboplastins of different origins. Although ETP was higher in the healthy controls, thrombin generation in FVII deficient patients was enough to sustain normal haemostasis. The expected thrombin generation patterns with increasing thromboplastin concentrations were confirmed for the patients in this study.