Menstrual blood loss measurement: validation of the alkaline hematin technique for feminine hygiene products containing superabsorbent polymers

Transcription

1 Menstrual blood loss measurement: validation of the alkaline hematin technique for feminine hygiene products containing superabsorbent polymers Julia L. Magnay, M.Sc., a Tracy M. Nevatte, Ph.D., a Vandana Dhingra, M.B.B.S., b and Shaughn O Brien, D.Sc. a,b a Institute for Science and Technology in Medicine, Guy Hilton Research Centre, Hartshill, Stoke on Trent, United Kingdom; and b Academic Unit of Obstetrics and Gynecology, University Hospital of North Staffordshire, Stoke on Trent, United Kingdom Objective: To validate the alkaline hematin technique for measurement of menstrual blood loss using ultra-thin sanitary towels that contain superabsorbent polymer granules as the absorptive agent. Design: Laboratory study using simulated menstrual fluid (SMF) and Always Ultra Normal, Long, and Night with wings sanitary towels. Setting: Keele Menstrual Disorders Laboratory. Patient(s): None. Intervention(s): None. Main Outcome Measure(s): Recovery of blood, linearity, and interassay variation over a range of SMF volumes applied to towels. Because of the variable percentage of blood in menstrual fluid, blood recovery was assessed from SMF constituted as 10%, 25%, 50%, and 100% blood. The lower limit of reliable detection and the effect of storing soiled towels for up to 4 weeks at 15 C 20 C, 4 C, and 20 C before analysis were determined. Result(s): Ninety percent recovery was reproducibly achieved up to 30 ml applied volume at all tested SMF compositions, except at low volume or high dilution equivalent to <2 ml whole blood. Samples could be stored for 3 weeks at all tested temperatures without loss of recovery. The technique was suitable for processing towels individually or in batches. Conclusion(s): The alkaline hematin technique is a suitable and validated method for measuring menstrual blood loss from Always Ultra sanitary towels that contain superabsorbent polymers. (Fertil Steril Ò 2010;94: Ó2010 by American Society for Reproductive Medicine.) Key Words: Alkaline hematin, superabsorbent polymer granules, ultra-thin sanitary towels, heavy menstrual bleeding, menstrual blood loss For research purposes, heavy menstrual bleeding (menorrhagia) is defined as a menstrual blood loss of >80 ml per cycle (1). In clinical practice, the impact on quality of life and a woman s self-perception of her own menstrual blood loss are key determinants in the diagnosis and treatment of heavy menstrual bleeding, yet the latter is widely recognized to be inaccurate, and specific validated qualityof-life methods are inadequate (2 5). Nevertheless, for many women the assessment of menstrual blood loss is probably the most important single parameter of their menstrual history, because it is on this basis that the decision is made to prescribe drugs or perform invasive surgical procedures such as hysterectomy. Accurate diagnosis of heavy menstrual bleeding requires precise measurement of menstrual blood loss. Originally developed in the 1960s, the alkaline hematin technique remains the definitive method for diagnosing this condition (1). It has undergone various modifications (6 8) but has only been validated using thick cotton-based sanitary towels and tampons. In recent years a new generation of ultrathin feminine hygiene products has become available, with greatly Received February 16, 2010; revised and accepted March 23, 2010; published online May 5, J.L.M. has nothing to disclose. T.M.N. has nothing to disclose. V.D. has nothing to disclose. S.O. has nothing to disclose. Supported in part by Bayer Schering Pharma. Reprint requests: Julia L. Magnay, M.Sc., Institute for Science and Technology in Medicine, Guy Hilton Research Centre, Thornburrow Drive, Hartshill, Stoke on Trent ST4 7QB, United Kingdom (FAX: +44 (0) ; j.l.magnay@bemp.keele.ac.uk). enhanced absorbent properties. The central core of these towels contains superabsorbent polymer granules that are capable of absorbing many times their own weight in fluid (9). Currently, the best-selling range of such feminine towels in the United States is Always Ultra with Wings (Proctor & Gamble, Cincinnati, OH) (10). With these facts in mind, we revalidated the alkaline hematin technique using three representative types of Always Ultra winged towels: Normal, Long, and Night, with increasing absorbance ratings, respectively. We set a target recovery of R90%, based on previous validation studies that used cotton-based products (4,8,11 14). MATERIALS AND METHODS Preparation of Reagents Research-designated human donor blood units were purchased from the National Blood Service (Bristol, United Kingdom). Stock solutions of simulated menstrual fluid (SMF) were prepared in 0.9% saline to give 10%, 25%, 50%, and 100% (no saline) solutions of whole blood, which were then stored at 4 C. Because menstrual fluid typically contains approximately 50% whole blood (15), we used this concentration of SMF for our main experiments. Sodium hydroxide solution (5% NaOH wt/vol) was freshly prepared before each assay. Determination of Linear Range The following volumes of 50% SMF were added to Always Ultra towels: Normal: 1, 5, 10, 15, and 20 ml; Long and Night: 1, 5, 2742 Fertility and Sterility â Vol. 94, No. 7, December /$30 Copyright ª2010 American Society for Reproductive Medicine, Published by Elsevier Inc. doi: /j.fertnstert

2 10, 15, 20, 25, and 30 ml. Towels were individually sealed in mm lidded plastic boxes for 1 week at room temperature. A blank towel of each type was included. A set of seven calibrators was prepared in separate containers, using the same volumes of 50% SMF. Three hundred milliliters of 5% NaOH were added to all samples. A reagent blank of NaOH was also set up. All boxes were sealed and incubated overnight at room temperature. To extract the alkaline hematin, towels were manually wrung once into the NaOH, replaced in the reagent for 1 hour, then wrung again and discarded. Aliquots of each alkaline hematin solution were centrifuged for 10 minutes at 13,000 rpm, and the absorbance of the supernatant measured at 546 nm against water. The reagent blank and appropriate towel blank absorbances were subtracted from the calibrator and test readings, respectively. A calibration curve was generated, comprising the volume of applied SMF vs. the measured absorbance at 546 nm. The volume of blood recovered (SMF volume/2) from each towel was determined by linear regression analysis (n ¼ 10 experiments). Use of a Single Whole-Blood Calibrator Blood recovery was determined for intermediate volumes of applied SMF between 0.5 and 25 ml. For these and subsequent experiments a single whole-blood calibrator was used rather than a calibration curve, to simulate the clinical setting where the precise proportion of blood in menstrual fluid is not known. This is analogous to using the patient s peripheral hemoglobin as a calibrator (measured as alkaline hematin) (7). A stock of 50% SMF was prepared from four pooled blood units, and the following volumes were applied to all towel types: ml in 0.5-mL increments; 3 10 ml in 1-mL increments; ml in 2-mL increments; and 25 ml (n ¼ 135 towels). Each volume was replicated at least twice per product type, and the towels were processed in seven separate groups in a randomized order, over a 3-week period. For each group, the whole-blood calibrator was prepared in triplicate by diluting an aliquot of the original pooled blood units 1:101 with 5% NaOH. Blood volume was calculated by the formula: Blood volume recovered ml ¼ ½ðA towel dþ A towel blank ŠV ð8þ; ða WB A NaOH Þ101 where A ¼ absorbance, d ¼ dilution factor if A was >, V ¼ total volume of NaOH, A WB ¼ mean calibrator absorbance, A NaOH ¼ reagent blank absorbance, and 101 ¼ calibrator dilution factor. SMF Composition Recovery of blood from Ultra towels was then investigated using 10%, 25%, or 100% SMF. The applied volumes were 1, 5, 10, and 20 ml for Normal towels and 1, 5, 10, 20, and 30 ml for Long and Night towels. All products were stored for 1 week at 4 C before analysis (n ¼ 6 for each composition of SMF). Batch-Processed Towels Batches of stained towels were stored together for 1 week at 4 Cin sealed 10-L buckets (one bucket per towel type). Three volume categories were tested: low, intermediate, and high (see Results for SMF volume applied and towel quantities). Blank towels were stored in a separate bucket but were treated in an identical manner. Five percent NaOH was added to each bucket, 300 ml per towel. The towels were processed, then three aliquots of well-mixed alkaline hematin solution were removed from each bucket, centrifuged, and the mean absorbance at 546 nm was used to calculate the volume of blood recovered (n ¼ 10 or 11 experiments for each volume category). Four-Week Stability Study Because all three towel types had shown similar absorbance characteristics in previous experiments, Ultra Long towels were tested as a midway representative for the stability study. Ten milliliters of 50% SMF were pipetted onto 36 Ultra Long towels, which were then divided into three equal groups, one for each incubation temperature. The stained towels were stored in sealed plastic boxes, at 20 C, 4 C, or ambient room temperature (15 C 20 C) for 1, 2, 3, or 4 weeks. Blank towels were included. Four 10-mL aliquots of whole blood were stored with the towels at each of the three incubation temperatures and were used as calibrators (12 in total), one aliquot per week of storage. At weekly intervals, three towels were processed from each group, using the corresponding calibrator. To test whether prolonged contact of SMF with superabsorbent polymers affected blood recovery, an identical series of Always Maxi Long Towels with Wings was simultaneously processed as a control group. These have the same absorbency rating as Ultra Long towels but do not contain polymer granules. RESULTS Determination of Linear Range Figure 1 shows the mean (SEM) blood recovery from individually processed towels, using 10 different blood units and calibration curves. The analytic range was linear up to the maximum volume tested. Recovery was R90% at all tested volumes for all towel types and was not significantly different between the products (one-way analysis of variance, P>.05). The mean blood recovery from 1 ml of applied SMF was 108% (Normal), 98% (Long), and 110% (Night). However, the corresponding interassay coefficients of variation (CV%) were 35.5, 27.0, and 27.5, which indicated imprecise recovery at low volume for all towel types. Precision progressively improved as the applied volume increased from 5 to 20 ml or from 5 to 30 ml, giving CV% values ranging from 10.6 to 6.3 (Normal), 13.4 to 5.6 (Long), and 9.4 to (Night). Use of a Single Whole-Blood Calibrator Figure 2 shows the blood recovery from 135 towels, using a single whole-blood calibrator and a range of SMF volumes between 0.5 and 25 ml. Across the complete volume spectrum, the mean (SEM) blood recovery was 93% (0.56). Ten samples gave <85% recovery, eight of which corresponded to <4 ml of applied SMF (<2 ml whole blood equivalent [WBE]). SMF Composition Table 1 depicts the mean percentage blood recovery from various compositions of SMF applied to towels. Recovery profiles were similar for all towel types. At the volumes tested, R90% recovery was achieved at 20 ml (2 ml WBE) in the 10% group; at 10 ml (2.5 ml WBE) in the 25% group; and at 5 ml (5 ml WBE) in the 100% group. Further experiments of the 100% group using incremental 1-mL volumes between 1 and 5 ml showed that >90% recovery was consistently achieved at 2 ml whole blood (n ¼ 3, data not shown). Batch-Processed Towels Table 2 shows the mean (SEM) percentage blood recovery from batch-processed towels at low, intermediate, and high volumes of Fertility and Sterility â 2743

3 FIGURE 1 Linear regression analysis of mean blood recovered from known volumes of 50% SMF applied to Always Ultra Normal, Long, and Night towels. Error bars depict SEM. The true value (100% recovery) is shown by the dotted line; n ¼ 10 experiments Normal y = x R 2 = Volume of 50% SMF applied (ml) FIGURE 2 Linear regression analysis of blood recovered from known volumes of 50% SMF applied to Always Ultra Normal, Long, and Night towels. Volumes tested were ml; n ¼ 135 towels. Composite data from all towel types are shown. 1 1 y = x R 2 = Volume of 50% SMF applied to towel (ml) 1 Long y = x R 2 = Volumeof 50% SMF applied (ml) Night y = 0.474x R 2 = Volume of 50% SMF applied (ml) applied SMF. Recovery was R94% for all towel types in all volume categories. The interassay CV% was %7.0 in all cases and was lowest at high volume. Four-Week Stability Study The mean percentage blood recovery was calculated from 10 ml of SMF applied to Ultra and Maxi Long towels stored at room temperature, 4 C, and 20 C for up to 4 weeks before analysis. For the first 3 weeks of storage, recovery was stable at 98% 102% and 100% 114% for the Ultra and Maxi products, respectively, at all tested temperatures. However, recovery at 4 weeks had markedly decreased to 86% (Ultra) and 90% (Maxi) in the towels stored at room temperature, although those kept at 4 C and 20 C were unaffected. DISCUSSION We modified and validated the alkaline hematin technique of Hallberg and Nilsson (1) for use with Always Ultra feminine towels that contain superabsorbent polymer granules as the absorptive agent. In contrast to the original technique, the hemoglobin level of our whole-blood calibrator was measured indirectly as alkaline hematin (7, 16), the extracted hemoglobin was centrifuged, not filtered (12), and blank towel absorbances were incorporated to negate any interference by the product constituents (8). Furthermore, the towels were briefly squeezed on two separate occasions during the incubation stage. This strategy markedly increases blood recovery from thick cotton-based sanitary products (12). Alkaline hematin was readily eluted from stained towels after an overnight incubation with NaOH followed by two wringing procedures, 1 hour apart. The total manipulation time per towel was approximately 30 seconds. Our technique was suitable for processing towels individually or in batches, and the analytic range was linear up to towel saturation levels. The absorbance characteristics of the three towel types were comparable; thus a single calibrator could be used, regardless of the towel type and blood volume being analyzed. Menstrual fluid typically contains approximately 50% blood, but wide interindividual variations have been observed (15, 17, 18). Validation studies of cotton-based towels have tended to use whole blood. However, we tested a range of blood compositions from 10% to 100% across a spectrum of volumes. Our 90% recovery target was reproducibly achieved, except at low volumes, for which there was a wide scatter of recovery, or at higher volumes of diluted SMF containing <2 ml WBE. On the basis of these data, we propose that the lower limit of reliable detection is 2 ml WBE, regardless of the total fluid volume. To simulate both the clinical and research setting, where there will be a delay between patient collection of towels and laboratory 2744 Magnay et al. Alkaline hematin assay validation Vol. 94, No. 7, December 2010

4 TABLE 1 Mean blood recovery from towels using various compositions of SMF. Volume SMF applied (ml) Mean blood volume recovered, ml Mean blood volume recovered, % (SEM) CV% 10% 25% 100% 10% 25% 100% 10% 25% 100% Normal (04) 59 (1) 84 (2) (1) 81 (1) 97 (1) (2) 92 (5) 102 (0.19) (4) 95 (7) 97 (0.46) Long (1) 61 (1) 82 (3) (1) 83 (2) 95 (0.16) (2) 91 (3) 100 (0.20) (5) 95 (6) 99 (0.33) (5) 93 (7) 94 (0.65) Night (1) 64 (1) 86 (4) (1) 86 (2) 96 (0.11) (2) 93 (3) 101 (0.19) (3) 96 (5) 100 (0.36) (5) 95 (7) 95 (0.68) Note: Mean recovered blood volume, mean percentage recovered blood, SEM, and interassay CV% from known volumes of 10%, 25%, and 100% SMF applied to Always Ultra Normal, Long, and Night towels; n ¼ 6 experiments. analysis, stained products were stored for up to 4 weeks at 15 C 20 C, 4 C, or 20 C before processing. Recovery was consistently above 90% at all temperatures for the first 3 weeks. However, we would not recommend storage of soiled towels at room temperature, first for aesthetic reasons and second because fluctuating ambient temperatures different from those tested here may have a detrimental effect on extraction efficiency. Various modifications of the original alkaline hematin technique have been reported for cotton-based products. These include the use of nonionic detergents, such as Alconox or Triton X, to wash the hemoglobin from soiled towels before conversion to hematin, and sodium carbonate solution (Na 2 CO 3 ) as an alternative alkaline agent (6, 19). Initial experiments in our laboratory tested these options with Always Ultra products. When the wash agent was added to stained towels, the polymer granules immediately swelled to form a hydrogel that trapped the hemoglobin in situ. Subsequent reaction with either 5% NaOH or 0.85 mol/l Na 2 CO 3 resulted in low and inconsistent blood recovery, as did overnight incubation of towels with Na 2 CO 3 alone (20). These strategies are patently unsuitable for towels containing superabsorbent polymers. Other studies with TABLE 2 Mean blood recovery from batch-processed towels. Volume category Volume SMF applied to towels, ml Total volume SMF applied, ml Mean blood volume recovered, ml Mean blood volume recovered, % (SEM) CV% Low Normal (8) 2 (1, 2, 3, 4) (0.18) 6.5 Long (8) 2 (1, 2, 3, 4) (0.19) 6.8 Night (8) 2 (1, 2, 3, 4) (0.15) 5.1 Intermediate Normal (5) 1, 5, 10, 15, (0.58) 7.0 Long (7) 1, 5, 10, 15, 20, 25, (1.09) 6.3 Night (7) 1, 5, 10, 15, 20, 25, (0.97) 5.6 High Normal (10) (1.05) 3.2 Long (7) (1.08) 3.2 Night (7) (1.19) 3.6 Note: Mean recovered blood volume, mean percentage recovered blood, SEM, and interassay CV% from known volumes of 50% SMF applied to Always Ultra Normal, Long, and Night towels that were batch-processed. The number of towels processed per batch is shown in parentheses. Mean values for low-, intermediate-, and high-volume categories are shown; n ¼ 10 or 11 experiments. Fertility and Sterility â 2745

5 cotton-based products have automated and accelerated the extraction procedure with NaOH, by using a Stomacher lab blender (Seward Ltd, West Sussex, United Kingdom) (7, 8, 16). This could be a feasible alternative to our overnight incubation stage but was not tested here. Laboratory methods of blood loss measurement are more accurate than visual estimation (21 23). The alkaline hematin technique remains the gold standard against which simpler, less-precise methods have been validated, such as the pictorial blood loss assessment chart (PBAC) (24), the menstrual pictogram (25), and soiled towel weight (26, 27). However, the following caveats should be observed. First, the PBAC/pictogram scoring systems are specific to cotton-based Kotex Maxi towels and cannot be used for products containing superabsorbent polymers, which show very different staining characteristics (20). Second, the PBAC, pictogram and towel weight estimate total menstrual fluid loss, not specifically blood loss. Because of the variable composition of blood in menstrual fluid, it is difficult to compare these methodologies directly with the alkaline hematin technique. In situations in which menstrual blood loss is an essential outcome parameter, for example, to assess the effectiveness of drug treatments in clinical trials or to provide reassurance to women with normal blood loss to refrain from seeking unnecessary treatment, the alkaline hematin technique is still a key diagnostic and monitoring tool. Because more women now use ultra-slim feminine products in preference to their maxi cotton-based counterparts, validation of the alkaline hematin method for towels that contain superabsorbent polymers provides an accurate measurement of menstrual blood loss that can be readily used in the clinical research setting. No specialized laboratory facilities were required for our methodology, apart from a sink large enough to accommodate a 10-L container and a cold storage facility for the towels. Because of the breathable Odor Lock Layer incorporated into Always Ultra feminine products, stained towel odor was minimal. Sodium hydroxide and screened human blood products were handled by experienced researchers using suitable personal protective equipment, in compliance with local health and safety policies. REFERENCES 1. Hallberg L, Nilsson L. Determination of menstrual blood loss. Scandinav J Clin Lab Invest 1964;16: National Institute for Health and Clinical Excellence. Clinical guidelines: heavy menstrual bleeding. London: RCOG Press, Hayes P, Hodgson H, Anderson AB, Turnbull AC. Measurement of menstrual blood loss in women with normal and excessive menstrual fluid volume. Obstet Gynecol 2001;98: Fraser IS, McCarron G, Markham R. A preliminary study of factors influencing perception of menstrual blood loss volume. Am J Obstet Gynecol 1984;149: Chimbira TH, Anderson ABM, Turnbull AC. 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