Genome-wide meta-analysis of phytosterols reveals five novel loci and a detrimental effect on coronary atherosclerosis.

Phytosterol serum concentrations are under tight genetic control. The relationship between phytosterols and coronary artery disease (CAD) is controversially discussed. We perform a genome-wide meta-analysis of 32 phytosterol traits reflecting resorption, cholesterol synthesis and esterification in six studies with up to 9758 subjects and detect ten independent genome-wide significant SNPs at seven genomic loci. We confirm previously established associations at ABCG5/8 and ABO and demonstrate an extended locus heterogeneity at ABCG5/8 with different functional mechanisms. New loci comprise HMGCR, NPC1L1, PNLIPRP2, SCARB1 and APOE. Based on these results, we perform Mendelian Randomization analyses (MR) revealing a risk-increasing causal relationship of sitosterol serum concentrations and CAD, which is partly mediated by cholesterol. Here we report that phytosterols are polygenic traits. MR add evidence of both, direct and indirect causal effects of sitosterol on CAD.

COVID-19 Infection in Sickle Cell Patients in a Developing Country: A Case Series.

Sickle cell disease is characterized by vaso-occlusive phenomena and haemolytic anaemia. There is a significant concern that the overlap of COVID-19 lung disease with acute chest syndrome that occurs in sickle cell patients may result in serious complications. Case reports of sickle cell patients with COVID-19 have been published. Here, we present a case series of COVID-19 infection in sickle cell patients in a developing country (Brazil). Only 10 patients tested positive so far for SARS-CoV-2 of 600 patients followed at our institution, of which 8 needed hospitalization (one in the intensive care unit), with no deaths. Even in a middle-income country, COVID-19 was reported to be relatively mild in sickle cell patients. In relation to risk factors, blood type O seems to confer some protection against developing severe COVID-19, a finding that could guide clinicians to adopt more clinical surveillance for patients with non-O blood type in sickle cell patients.

Influence of Cancer Susceptibility Gene Mutations and ABO Blood Group of Pancreatic Cancer Probands on Concomitant Risk to First-Degree Relatives.

BACKGROUND: ABO blood group is associated with pancreatic cancer risk. Whether ABO blood group alone or when combined with inherited mutation status of index pancreatic cancer cases (probands) can enhance pancreatic cancer risk estimation in first-degree relatives (FDR) is unclear. We examined FDRs' risk for pancreatic cancer based on probands' ABO blood group and probands' cancer susceptibility gene mutation status. METHODS: Data on 23,739 FDRs, identified through 3,268 pancreatic cancer probands, were analyzed. Probands' ABO blood groups were determined serologically or genetically, and 20 cancer susceptibility genes were used to classify probands as "mutation-positive" or "mutation-negative." SIRs and 95% confidence intervals (CI) were calculated, comparing observed pancreatic cancer cases in the FDRs with the number expected in SEER-21 (reference population). RESULTS: Overall, FDRs had 2-fold risk of pancreatic cancer (SIR = 2.00; 95% CI = 1.79-2.22). Pancreatic cancer risk was higher in FDRs of mutation-positive (SIR = 3.80; 95% CI = 2.81-5.02) than mutation-negative (SIR = 1.79; 95% CI = 1.57-2.04) probands (P < 0.001). The magnitude of risk did not differ by ABO blood group alone (SIRblood-group-O = 1.57; 95% CI = 1.20-2.03, SIRnon-O = 1.83; 95% CI = 1.53-2.17; P = 0.33). Among FDRs of probands with non-O blood group, pancreatic cancer risk was higher in FDRs of mutation-positive (SIR = 3.98; 95% CI = 2.62-5.80) than mutation-negative (SIR = 1.66; 95% CI = 1.35-2.03) probands (P < 0.001), but risk magnitudes were statistically similar when probands had blood group O (SIRmutation-positive = 2.65; 95% CI = 1.09-5.47, SIRmutation-negative = 1.48; 95% CI = 1.06-5.47; P = 0.16). CONCLUSIONS: There is a range of pancreatic cancer risk to FDRs according to probands' germline mutation status and ABO blood group, ranging from 1.48 for FDRs of probands with blood group O and mutation-negative to 3.98 for FDRs of probands with non-O blood group and mutation-positive. IMPACT: Combined ABO blood group and germline mutation status of probands can inform pancreatic cancer risk estimation in FDRs.

An Investigation of ABO Blood Type and the Platelet Delta Granule Storage Pool.

Individuals with bleeding tendencies are more likely to have blood type O than blood types A, B, or AB. Platelet storage pool deficiencies are a lesser-known group of bleeding disorders which often go undiagnosed and may account for a significant number of patients with unexplained bleeding defects. We hypothesized that patients with platelet δ-storage pool deficiency might also have a predominance of type O blood. A retrospective review of medical records of 2,020 patients with unexplained bleeding and evaluated for δ-storage pool deficiency was performed. Correlations between dense granule numbers, blood type, and von Willebrand factor were analyzed for statistical differences. 51.5% of blood samples were blood type O compared to an incidence of 44.0% in the U.S. population. There was a significant association of vWF and blood type O but not with the delta storage pool. There is a preponderance of blood type O in the study population compared to the U.S. population. There is no statistically significant link between blood type O and lower dense granule numbers in this study.

ABO Blood Group Differentials on Survival in Hepatocellular Carcinoma Patients Treated with Chemoembolization.

BACKGROUND: The association between ABO blood group and the prognosis of hepatocellular carcinoma (HCC) remains unclear. We investigated the impact of ABO blood groups as a prognostic factor in HCC patients treated with transarterial chemoembolization (TACE). MATERIALS AND METHODS: We revisited records of all HCC patients who underwent TACE between January 2007 and December 2019 at a tertiary care hospital. The inclusion criteria were HCC patients, Child-Pugh score A5-B7, and treated with TACE monotherapy. The baseline characteristics of each patient were compared against their blood group and the survival analysis was carried out using Cox's regression. With Bonferroni adjustment for multiple comparisons, P-values <.0125 were considered statistically significant. RESULTS: Of 211 eligible patients, the frequencies of blood groups O, A, B, and AB were 89, 54, 56, and 12, respectively. Their respective months of median survival were 41, 20, 21, and 42. After adjustments in the six-and-twelve criteria and Child-Pugh scores, and using blood group O as the referent group, the coefficients (SE) of groups A, B, and AB were 0.69 (0.24), 0.47 (0.23), and 0.49 (0.49), respectively. A significant difference in survival was found only between patients with blood group O vs A (hazard ratio, 2.00; confidence interval, 1.25-3.21). CONCLUSIONS: ABO blood group is associated with the prognosis of HCC patients treated with TACE monotherapy. In our data, patients with blood group O tended to have the best survival. However, only blood group A patients had a significantly shorter survival rate comparing to blood group O.

Analysis of ABO grouping discrepancies among patients from a tertiary hospital in Korea.

BACKGROUND: Accurate ABO typing is essential for preventing ABO incompatibility reactions. However, the causes of ABO grouping discrepancy has not been sufficiently studied, and it may vary among different ethnic populations. Thus, the aim of this retrospective study was to investigate the causes of ABO discrepancy in the East Asian population. MATERIALS AND METHODS: A retrospective observational study on ABO typing discrepancy among patients in a tertiary hospital was carried out using the electronic medical record database of Samsung Medical Center (Seoul, Korea) between July 2016 and May 2019. RESULTS: ABO grouping was performed on 551,959 blood samples during the study period; 1468 events of serologic ABO discrepancy were determined from 1334 (0.24 %) samples. A total of 134 samples (0.02 %) presented multiple causes of ABO discrepancy. Weak/missing serum reactivity (594, 40.5 %) was the most frequent reason for ABO discrepancy, followed by extra serum reactivity (370, 25.2 %), weak/missing red cell reactivity (267, 18.2 %), mixed-field red cell reactivity (176, 12.0 %), and extra red cell reactivity (61, 4.2 %). In the category of weak/missing red cell reactivity, ABO subgroup was the most common reason, and using ABO genotyping, 26.2 % of the cases genotyped were found to be related to the cis-AB allele. CONCLUSIONS: Our results suggest that the incidence and cause of ABO typing discrepancies vary among institutes and ethnic groups. Our data helps to better understand and facilitate the resolution of ABO typing discrepancies in patients.

The rebirth of the cool: a narrative review of the clinical outcomes of cold stored low titer group O whole blood recipients compared to conventional component recipients in trauma.

There has been renewed interest in the use of low titer group O whole blood (LTOWB) for the resuscitation of civilian casualties. LTOWB offers several advantages over conventional components such as providing balanced resuscitation in one bag that contains less additive/preservative solution than an equivalent volume of conventional components, is easier and faster to transfuse than multiple components, avoids blood product ratio confusion, contains cold stored platelets, and reduces donor exposures. The resurgence in its use in the resuscitation of civilian trauma patients has led to the publication of an increasing number of studies on its use, primarily amongst adult recipients but also in pediatric patients. These studies have indicated that hemolysis does not occur amongst adult and pediatric non-group O recipients of a modest quantity of LTOWB. The published studies to date on mortality have shown conflicting results with some demonstrating a reduction following LTOWB transfusion while most others have not shown a reduction; there have not been any studies to date that have found significantly increased overall mortality amongst LTOWB recipients. Similarly, when other clinical outcomes, such as venous thromboembolism, sepsis, hospital or intensive care unit lengths of stay are evaluated, LTOWB recipients have not demonstrated worse outcomes compared to conventional component recipients. While definitive proof of the trends in these morbidity and mortality outcomes awaits confirmation in randomized controlled trials, the evidence to date indicates the safety of transfusing LTOWB to injured civilians.

The association of ABO blood group with the asymptomatic COVID-19 cases in India.

The COVID-19 pandemic resulted in multiple waves of infection worldwide. The large variations in case fatality rate among different geographical regions suggest that the human susceptibility against this virus varies substantially. Several studies from different parts of the world showed a significant association of ABO blood group and COVID-19 susceptibility. It was demonstrated that individuals with blood group O are at the lower risk of coronavirus infection. To establish the association of ABO blood group in SARS-CoV-2 susceptibility, we for the first time analysed SARS-CoV-2 neutralising antibodies among 509 individuals, collected from three major districts of Eastern Uttar Pradesh region of India. Interestingly, we found neutralising antibodies in a significantly higher percentage of people with blood group AB (0.36) followed by B (0.31), A (0.22) and lowest in people with blood group O (0.11). We further estimated that people with blood group AB are at comparatively higher risk of infection than other blood groups. Thus, among the asymptomatic SARS-CoV-2 recovered people blood group AB has highest, whilst individuals with blood group O has lowest risk of infection.

Safety profile of low-titer group O whole blood in pediatric patients with massive hemorrhage.

BACKGROUND: Low-titer Group O Whole Blood (LTOWB) is used with increasing frequency in adult and pediatric trauma and massive bleeding transfusion protocols. There is a risk of acute hemolytic reactions in non-group O recipients due to the passive transfusion of anti-A and anti-B in the LTOWB. This study investigated the hemolysis risk among pediatric recipients of LTOWB. STUDY DESIGN AND METHODS: Blood bank records were queried for pediatric recipients of LTOWB between June 2016 and August 2020 and merged with clinical data. The primary outcome was laboratory evidence of hemolysis as manifested by changes in lactate dehydrogenase (LDH), haptoglobin, total bilirubin, reticulocyte count, potassium, and creatinine. Per protocol, these values were collected on hospital days 0-2 for recipients of LTOWB. Transfusion reactions were reported to the hospital's blood bank. RESULTS: Forty-seven children received LTOWB transfusion between 2016 and 2020; 21 were group O and 26 were non-group O. The groups were comparable in terms of the total volume of transfused blood products, demographics, and clinical outcomes. The most common indication for LTOWB transfusion was hemorrhagic shock due to trauma. There were no clinically or statistically significant differences in baseline, post-transfusion day 1, or post-transfusion day 2 hemolysis markers between the group O and non-group O LTOWB recipients. There were no adverse events or transfusion reactions reported. DISCUSSION: Use of up to 40 ml/kg of LTOWB appears to be serologically safe for children in hemorrhagic shock.

Survey to inform trial of low-titer group O whole-blood compared to conventional blood components for children with severe traumatic bleeding.

BACKGROUND: Low-titer group O whole-blood (LTOWB) is being used for children with life-threatening traumatic bleeding. A survey was conducted to determine current LTOWB utilization and interest in participation in a randomized control trial (RCT) of LTOWB versus standard blood component transfusion in this population. STUDY DESIGN AND METHODS: Transfusion medicine (TM) directors and pediatric trauma directors at 36 US children's hospitals were surveyed by e-mail in June 2020. Hospitals were selected by participation in the Massive Transfusion Epidemiology and Outcomes in Children Study or being among the largest 30 children's hospitals by bed capacity per the Becker Hospital Review. RESULTS: The response rate was 83.3% (30/36) from TM directors and 88.9% (32/36) from trauma directors. The median of massive transfusion protocol activations for traumatic bleeding was reported as 12 (IQR 5.8-20) per year by TM directors. LTOWB was used by 18.8% (6/32) of trauma directors. Survey responses indicate that 86.7% (26/30) of TM directors and 90.6% (29/32) of trauma directors either moderately or strongly agree that a LTOWB RCT is important to perform. About 83.3% (25/30) of TM directors and 93.8% (30/32) of trauma directors were willing to participate in the proposed trial. About 80% (24/30) of TM directors and 71.9% (23/32) of trauma directors would transfuse RhD+ LTOWB to male children, but fewer would transfuse Rh + LTOWB to females [20% (6/30) TM directors and 37.5% (12/32) of trauma directors]. CONCLUSIONS: A majority of respondents supported an RCT comparing LTOWB to component therapy in children with severe traumatic bleeding.

Blood group AB increases risk for surgical necrotizing enterocolitis and focal intestinal perforation in preterm infants with very low birth weight.

Necrotizing enterocolitis (NEC) and focal intestinal perforation (FIP) are two of the most common emergencies of the gastrointestinal tract in preterm infants with very low birth weight (VLBW, birth weight < 1500 g). Identification of risk factors among these children is crucial for earlier diagnosis and prompt intervention. In this study, we investigated a relationship between ABO blood groups and the risk for surgical NEC/FIP. We genotyped the ABO locus (rs8176746 and rs8176719) in VLBW infants enrolled in a prospective, population-based cohort study of the German Neonatal Network (GNN). Of the 10,257 VLBW infants, 441 (4.3%) had surgical NEC/FIP. In univariate analyses, the blood group AB was more prevalent in VLBW infants with surgical NEC/FIP compared to non-AB blood groups (OR 1.51, 95% CI 1.07-2.13, p = 0.017; absolute risk difference 2.01%, 95% CI 0.06-3.96%). The association between blood group AB and surgical NEC/FIP was observed in a multivariable logistic regression model (OR of 1.58, 95% CI 1.10-2.26, p = 0.013) as well. In summary, our study suggests that the risk of surgical NEC and FIP is higher in patients with blood group AB and lower in those having non-AB blood groups.

Genomic Association vs. Serological Determination of ABO Blood Types in a Chinese Cohort, with Application in Mendelian Randomization.

ABO blood system is an inborn trait determined by the ABO gene. The genetic-phenotypic mechanism underneath the four mutually exclusive and collectively exhaustive types of O, A, B and AB could theoretically be elucidated. However, genetic polymorphisms in the human populations render the link elusive, and importantly, past studies using genetically determined rather than biochemically determined ABO types were not and could not be evaluated for the inference errors. Upon both blood-typing and genotyping a cohort of 1008 people of the Han Chinese population, we conducted a genome-wide association study in parallel with both binomial and multinomial log-linear models. Significant genetic variants are all mapped to the ABO gene, and are quantitatively evaluated for binary and multi-class classification performances. Three single nucleotide polymorphisms of rs8176719, rs635634 and rs7030248 would together be sufficient to establish a multinomial predictive model that achieves high accuracy (0.98) and F1 scores (micro 0.99 and macro 0.97). Using the set of identified ABO-associated genetic variants as instrumental variables, we demonstrate the application in causal analysis by Mendelian randomization (MR) studies on blood pressures (one-sample MR) and severe COVID-19 with respiratory failure (two-sample MR).

Pre-transplant donor-type red cell transfusion is a safe and effective strategy to reduce isohemagglutinin titers and prevent donor marrow infusion reactions in major ABO-mismatched transplants.

ABO incompatibility is not a barrier to allogeneic stem cell transplant but may result in acute hemolytic reactions. As stem cell product manipulation is cumbersome, we are reporting the effectiveness and safety of donor-type red cell infusion as a method of reducing acute hemolytic reaction while using marrow as stem cell source. In major ABO-mismatched bone marrow transplants, manipulation of marrow product requires expertise and expensive equipment, which may not be readily available to transplant centers in low- and middle-income regions. The aim behind our study is to report a safe and effective strategy to reduce isohemagglutinin titers and prevent donor marrow infusion reactions in major ABO-mismatched transplants. We retrospectively analyzed 303 consecutive allogeneic bone marrow transplants (BMTs) for beta thalassemia major, between August 2015 and March 2020, with either major (n = 41) or bidirectional (n = 14) mismatches. When isohemagglutinin titers were 1:32 or higher, donor-type packed red blood cell was divided into 4 aliquots, irradiated and administered over 4 days at incremental volumes. Patients were observed for hemolytic reaction, and if no reaction, bone marrow was infused without manipulation. Out of 55 patients, 20 received donor-type blood infusion. Twelve patients showed evidence of mild hemolysis. None developed severe hemolytic or anaphylactic reaction. Titers were rechecked in 14 patients and all had reduction in titers, except for one. Our experience demonstrated that donor-type PRBC infusion is safe and effective in preventing acute hemolysis in major ABO-mismatched stem cell transplants even with bone marrow as graft source.

Impact of ABO blood group on bleeding complications after surgery for acute type A aortic dissection.

Excessive bleeding is a serious complication associated with impaired survival after surgery for acute type A aortic dissection (ATAAD). Different ABO blood groups are associated with variable levels of circulating von Willebrand factor and therefore potentially altered risks of surgical haemorrhage. The current study aimed to assess the impact of blood group on bleeding complications after ATAAD surgery. This was a retrospective cohort study including 336 patients surgically treated for ATAAD between January 2004 and January 2019. Patients with blood group O were compared with non-O patients. In total, 152 blood group O patients were compared with 184 non-O patients. There were no differences in rates of massive bleeding (27.0 vs. 25.5%, P = 0.767) or re-exploration for bleeding (16.4 vs. 13.0%, P = 0.379) in blood group O and non-O patients, respectively. Median chest tube output 12 h after surgery was 520 ml (350-815 ml) in blood group O and 490 ml (278-703 ml) in non-O patients (P = 0.229). Blood group O patients received more fibrinogen concentrate (6.1 ±â€Š4.0 vs. 4.9 ±â€Š3.3 g, P = 0.023) but administered units of packed red blood cells [5 (2-8) vs. 4 (2-9) U, P = 0.736], platelets [4 (2-4) vs. 3 (2-5) U, P = 0.521] or plasma [4 (1-7) vs. 4 (0-7) U, P = 0.562] were similar. This study could not demonstrate any association between blood group and bleeding after surgery for ATAAD. It cannot be ruled out that potential differences were levelled out by blood group O patients receiving significantly more fibrinogen concentrate.

Blood group O convalescent plasma donations have significantly lower levels of SARS-CoV-2 IgG antibodies compared to blood group A donations.

BACKGROUND: COVID-19 convalescent plasma (CCP) is plasma collected from individuals who have recovered from SARS-CoV-2 infection. The FDA Emergency Use Authorization restricts use of CCP to high-titer units only. The purpose of this study was to determine if donor ABO blood group was associated with SARS-CoV-2 antibody response, and subsequent qualification as high-titer CCP. METHODS: All CCP donations collected from April 21, 2020 to September 1, 2020 were included. The Abbott ARCHITECT semi-quantitative chemiluminescent microparticle immunoassay was used to assess IgG antibodies to the nucleocapsid protein of SARS-CoV-2. Units with a S/C value ≥4.5 were considered high titer. RESULTS: A total of 232 CCP donations were evaluated. There were no significant differences in the distribution of sex, age, and interval from symptom resolution to donation by ABO blood group. The mean SARS-CoV-2 IgG antibody S/C value was significantly lower in blood group O donations (3.6), compared to blood group A (5.0) donations (p < .001). There was no difference in antibody response between the other blood group pairings. Blood group O donations resulted in a lower percentage of high-titer units (35%), compared to blood group A (60%), B (58%), and AB (65%) donations. CONCLUSION: Blood group O donations were found to have significantly lower levels of SARS-CoV-2 IgG nucleocapsid antibodies compared to blood group A donations and were less likely to produce CCP units that qualified as high titer. These findings may aid donor recruitment to promote availability of high-titer CCP to meet patient needs.

Adverse events after low titer group O whole blood versus component product transfusion in pediatric trauma patients: A propensity-matched cohort study.

BACKGROUND: Low titer group O whole blood (LTOWB) is used as the initial resuscitative fluid in an increasing number of pediatric trauma and massive bleeding transfusion protocols. There is little data on adverse events following its transfusion in pediatric trauma patients. STUDY DESIGN AND METHODS: Blood bank records were queried for pediatric recipients of at least one unit of red blood cells (RBCs) (component group) or LTOWB (LTOWB group) within 24 h of admission between May 2013 and August 2020. Subjects with early death (<72 h) were excluded. Propensity-score matching of LTOWB and component groups was performed. Adverse events were recorded, including transfusion reaction, thromboembolism, acute kidney injury, sepsis, and organ failure based on PELOD-2 score, along with hospital and ICU length of stay (LOS) and ventilator days. RESULTS: Thirty-six LTOWB recipients were matched to 36 conventional component recipients. Subjects were 52% male, with blunt injury mechanism (82%), median (IQR) injury severity score = 27 (21-35), and 26% in-hospital mortality. The groups were well matched in terms of demographics and injury characteristics. There were no clinically or statistically significant differences in adverse outcomes including reported transfusion reaction, organ failure, acute kidney injury, sepsis/bacteremia, and venous thromboembolism. Hospital LOS, ventilator days, mortality, and functional disability at discharge were also not significantly different. The LTOWB group had significantly shorter ICU LOS compared to the component group. CONCLUSION: LTOWB transfusion did not increase the risk of adverse events in children. However, larger studies are required to confirm these results.

Does blood type affect the COVID-19 infection pattern?

Among the many aspects that characterize the COVID-19 pandemic, two seem particularly challenging to understand: i) the great geographical differences in the degree of virus contagiousness and lethality that were found in the different phases of the epidemic progression, and, ii) the potential role of the infected people's blood type in both the virus infectivity and the progression of the disease. A recent hypothesis could shed some light on both aspects. Specifically, it has been proposed that, in the subject-to-subject transfer, SARS-CoV-2 conserves on its capsid the erythrocytes' antigens of the source subject. Thus these conserved antigens can potentially cause an immune reaction in a receiving subject that has previously acquired specific antibodies for the source subject antigens. This hypothesis implies a blood type-dependent infection rate. The strong geographical dependence of the blood type distribution could be, therefore, one of the factors at the origin of the observed heterogeneity in the epidemics spread. Here, we present an epidemiological deterministic model where the infection rules based on blood types are taken into account, and we compare our model outcomes with the exiting worldwide infection progression data. We found an overall good agreement, which strengthens the hypothesis that blood types do play a role in the COVID-19 infection.

Variation of anti-A and anti-B titers in group O potential blood donors: A pilot study.

BACKGROUND: Resuscitation with fresh whole blood is vital to preserving life on the battlefield. Transfusing low titer O whole blood (LTOWB), defined as anti-A and anti-B titer levels of <1:256, is safe because LTOWB alleviates the risk for hemolytic transfusion reactions. Because of possible variations in titer levels over time, a study was needed using US Navy and Marine Corps personnel to assess how these titers change across two assessments. METHODS: Retrospective data from group O marines and sailors (M = 25 years of age; range, 19-35 years) stationed in the San Diego region were acquired from the Armed Services Blood Program and the Composite Health Care System. Of 972 group O donors between January 2016 and November 2019, 55 donors with 2 samples were identified (N = 55). Analysis included contrasting rates of high (≥1:256) and low (<1:256) anti-A and anti-B titers on the initial and second blood tests, along with the time between testings. RESULTS: The average time between testing was 332 days (range, 35-1,121 days), which far exceeded the recommended 90-day interval (p < 0.00001). Only 45% met the 90-day recommendation. Titer status changed frequently, from low to high (anti-A, 18%; anti-B, 13%; LTOWB to not LTOWB, 21%) or from high to low (anti-A, 62%; anti-B, 78%; not LTOWB to LTOWB, 62%). CONCLUSIONS: Anti-A and anti-B titers change frequently enough to warrant testing immediately before deployment and even during deployment. The observed time elapsed between testing is unacceptably long. The present pilot study provides a foundation for a larger formal study to more fully characterize titer changes over repeated testing. LEVEL OF EVIDENCE: Diagnostic test, level IV.