scholarly journals Comparison of various principles of coagulation tests in handling hemolysed blood samples

2021 ◽  
Vol 7 (4) ◽  
pp. 188-193
Author(s):  
Dr. Vani Krishnamurthy ◽  
◽  
Rubiya Ahmad ◽  
Keyword(s):  
Prothrombin Time ◽  
Test Results ◽  
Coagulation Test ◽  
Predictive Values ◽  
Background Rejection ◽  
Coagulation Testing ◽  
Coagulation Tests ◽  
The Mean ◽  
Repeat Sampling ◽  
Lost Opportunity

Background: Rejection of hemolysed samples for coagulation test is the standard practice.However, when clinicians deal with extremely sick patients where repeat sampling is difficult toobtain, rejection of the sample is a lost opportunity for the lab physician to assist inpatient care.Proceeding with the test and providing a clinically helpful interpretation of the results will ensure theactive participation of the laboratory physician. Different principles of coagulation testing handle thehemolysed samples differently. It is essential to know the best principle to proceed with thehemolysed sample if need be. This study set out to estimate the predictive values of post-hemolyticsample coagulation test results with various coagulation test principles. Methods: This is aprospective experimental study where the non-hemolysed samples were processed for coagulationtests. Part of the sample was deliberately hemolysed, and the coagulation tests were repeated.Results: Two hundred and forty-eight samples were studied. A median of 11% hemolysis wasachieved experimentally. The mean difference in prothrombin time between pre and post hemolyticsamples with normal PT was 0.9 and with abnormal PT, it was 1.1 seconds. The same for APTT was4.9 and 1.1 seconds, respectively. The majority of the samples showed prolonged coagulation posthemolysis. Positive (PPV) and negative (NPV) predictive values for prothrombin time are 97.3 and73.4%, respectively. Similarly, PPV and NPV for APTT are 97.4 and 47.1%, respectively.Conclusions: Samples with normal values after hemolysis are more likely to be normal.

The effects of transport by car on coagulation tests

2017 ◽  
Vol 55 (12) ◽  
Author(s):  
Merve Ergin ◽  
Serpil Erdogan ◽  
Onur Akturk ◽  
Ozcan Erel
Keyword(s):  
Clinical Decision ◽  
Control Group ◽  
Test Results ◽  
Mechanical Agitation ◽  
Blood Samples ◽  
Decision Level ◽  
Baseline Group ◽  
Coagulation Tests ◽  
The Mean ◽  
Clinically Significant

AbstractBackground:This research investigated the effects of the transport of blood samples between centers/laboratories by car on coagulation tests.Methods:Five tubes of blood samples were taken from 20 healthy volunteers. The samples consisted of a baseline (control) group, centrifuged and noncentrifuged transported samples; centrifuged and noncentrifuged untransported samples. The groups of centrifuged and noncentrifuged samples were transported by car for 2 h. The centrifuged and noncentrifuged untransported samples were incubated in the laboratory until the transported samples arrived. Prothrombin time (PT) and activated partial thromboplastin time (APTT) tests were conducted for all samples.Results:Significant differences between the baseline group and the centrifuged and noncentrifuged transported samples and the noncentrifuged untransported samples were found for APTT levels (p<0.05, for all). In addition, significant mean percentage differences in PT values were found between the baseline group and the noncentrifuged transported samples (p<0.001) and the noncentrifuged untransported samples (p=0.005). The mean level of PT in the noncentrifuged transported samples was outside the upper limit of the clinical decision level.Conclusions:Noncentrifuged transported samples showed clinically significant differences in PT test results that may have stemmed from mechanical agitation during transportation. Therefore, we recommend not transporting noncentrifuged specimens for PT testing by car.

Monitoring Treatments with Unfractionated Heparin: CTAD Must Be Used Instead of Citrate as the Anticoagulant Solution When Using Partial-Draw Collection Tubes.

Blood ◽  
2009 ◽  
Vol 114 (22) ◽  
pp. 2091-2091
Author(s):  
Pierre A. Toulon ◽  
Lién Abecassis ◽  
Motalib Smahi ◽  
Catherine Ternisien
Keyword(s):  
Unfractionated Heparin ◽  
Platelet Activation ◽  
Conflicts Of Interest ◽  
Vitamin K Antagonists ◽  
Heparin Therapy ◽  
Factor V ◽  
Test Results ◽  
Coagulation Testing ◽  
Coagulation Tests ◽  
Routine Coagulation

Abstract Abstract 2091 Poster Board II-68 Collecting small volumes of blood may be necessary, particularly in pediatrics, or in case of difficult or recurrent sampling. The aim of this multicenter study, involving four hemostasis laboratories, was to compare hemostasis test results in plasma samples obtained using partial- and full-draw evacuated polymer collection tubes containing 0.109 M sodium citrate (1 vol./9 vol.) as the anticoagulant solution (VenoSafeTM, Terumo Europe, Leuven, Belgium). For that purpose, blood was collected into one full- and one partial-draw tube from patients on vitamin K antagonists (VKA, n=100), unfractionated heparin (UFH, n=89), or a low molecular weight derivative (LMWH, n=52), as well as from 136 untreated patients, including 13 hemophiliacs. Routine coagulation tests i.e. PT/INR, aPTT, fibrinogen, and factor V, as well as factor VIII and anti-FXa activity when applicable, were measured using the routine techniques at each participating center. In addition, plasma PF-4 level, evaluated using an ELISA, was investigated in a subset of 36 healthy controls. In untreated patients incl. hemophiliacs as well as in those on either VKA or LMWH, no significantly relevant discrepancy (Bland-Altman) was found between tests results obtained using full- and partial-draw tubes. In contrast, anti-FXa activity in patients on UFH was significantly lower in partial- than in full-draw tubes [median=0.33 IU/mL (range: 0.00-1.11) vs. 0.39 (range: 0.05-1.32) respectively, p<0.0001]. Similarly, aPTT was significantly shorter in partial- than in the full-draw tubes, whereas other test results were not significantly different in the two tubes. That discrepancy was likely to be related to higher amount of PF4 released in plasma after increased platelet activation in partial-draw than in full-draw tubes [392 U/mL (range: 138-971) vs. 177 (range: 52-460) respectively, n=36; p<0.005)]. To further support that hypothesis, blood was collected, from 101 patients on UFH and from 104 untreated patients, into one partial-draw collection tube containing CTAD, a mixture of citrate and inhibitors of platelet activation, as the anticoagulant solution and one full-draw citrated tube, obtained from the same manufacturer. Comparison performed according to Bland-Altman of anti-FXa obtained in the two tubes failed to demonstrate any relevant difference, with a mean bias of +0.02 IU/mL that was identical throughout the measuring range of values [median=0.22 IU/mL (range: 0.06-1.16) vs. 0.20 (range: 0.03-1.15) respectively, n=101]. Moreover, in those patients on UFH, aPTT and other routine coagulation tests were not significantly different in the two tubes and the same applied to test results obtained in the plasma from untreated patients. These results suggest that samples collected into partial-draw citrated tubes allow accurate routine coagulation testing in all patients but those requiring UFH assessment, in which their use could lead to a significant underestimation of anticoagulation. In such cases, partial-draw tubes containing CTAD could be validly used to monitor heparin therapy, as well as to perform routine coagulation testing. Disclosures: No relevant conflicts of interest to declare.

Coagulation Testing in Acute Ischemic Stroke Patients Taking Non-Vitamin K Antagonist Oral Anticoagulants

2020 ◽  
Vol 154 (Supplement_1) ◽  
pp. S101-S102
Author(s):  
Y S Kamel
Keyword(s):  
Ischemic Stroke ◽  
Acute Ischemic Stroke ◽  
Oral Anticoagulants ◽  
False Negative ◽  
International Normalized Ratio ◽  
Vitamin K Antagonist ◽  
Activated Partial Thromboplastin Time ◽  
Test Results ◽  
Coagulation Testing ◽  
Coagulation Tests

Abstract Introduction/Objective In patients who present with acute ischemic stroke while on treatment with non-vitamin K antagonist oral anticoagulants (NOACs), coagulation testing is necessary to confirm the eligibility for thrombolytic therapy. We evaluated the current use of coagulation testing in routine clinical practice in patients who were on NOAC treatment at the time of acute ischemic stroke. Methods Prospective multicenter observational RASUNOA registry (Registry of Acute Stroke Under New Oral Anticoagulants). Results of locally performed nonspecific (international normalized ratio, activated partial thromboplastin time, and thrombin time) and specific (antifactor Xa tests, hemoclot assay) coagulation tests were documented. The implications of test results for thrombolysis decision-making were explored. Results In the 290 patients enrolled, nonspecific coagulation tests were performed in ≥95% and specific coagulation tests in 26.9% of patients. Normal values of activated partial thromboplastin time and international normalized ratio did not reliably rule out peak drug levels at the time of the diagnostic tests (false-negative rates 11%-44% [95% confidence interval 1%-69%]). Twelve percent of patients apparently failed to take the prescribed NOAC prior to the acute event. Only 5.7% (9/159) of patients in the 4.5-hour time window received thrombolysis, and NOAC treatment was documented as main reason for not administering thrombolysis in 52.7% (79/150) of patients. Conclusion NOAC treatment currently poses a significant barrier to thrombolysis in ischemic stroke. Because nonspecific coagulation test results within normal range have a high false-negative rate for detection of relevant drug concentrations, rapid drug-specific tests for thrombolysis decision-making should be established.

scholarly journals Comparison of the New Viscoelastic Coagulation Analyzer ClotPro® With ROTEM® Delta and Conventional Coagulation Tests in Critically Ill Patients With COVID-19

2021 ◽  
Vol 8 ◽  
Author(s):  
Lukas Infanger ◽  
Christoph Dibiasi ◽  
Eva Schaden ◽  
Stefan Ulbing ◽  
Marion Wiegele ◽  
...  
Keyword(s):  
Critically Ill ◽  
Critically Ill Patients ◽  
Factor Xa ◽  
Test Results ◽  
Strong Correlations ◽  
Strength Parameters ◽  
Clot Strength ◽  
Viscoelastic Parameters ◽  
Coagulation Testing ◽  
Coagulation Tests

Background: Viscoelastic coagulation testing has been suggested to help manage coagulopathy in critically ill patients with COVID-19. However, results from different viscoelastic devices are not readily comparable. ClotPro® is a novel thromboelastometry analyzer offering a wider range of commercially available assays.Methods: We compared the results from ClotPro with results from the well-established ROTEM® Delta device and conventional coagulation tests in critically ill patients with COVID-19.Results: Viscoelastic parameters indicated the presence of a potentially hypercoagulable state in the majority of patients. In up to 95 paired measurements, we found strong correlations between several parameters routinely used in clinical practice: (i) EX test vs. EXTEM CT, A5, A10, MCF, (ii) IN test vs. INTEM A5, A10, MCF, and (iii) FIB test vs. FIBTEM A5, A10, MCF (all R &gt; 0.7 and p &lt; 0.001). In contrast, IN test CT vs. INTEM CT showed only a moderate correlation (R = 0.53 and p &lt; 0.001). Clot strength parameters of both devices exhibited strong correlations with platelet counts and fibrinogen levels (all R &gt; 0.7 and p &lt; 0.001). Divergent correlations of intrinsically activated assays with aPTT and anti-factor Xa activity were visible. Regarding absolute differences of test results, considerable delta occurred in CT, CFT, and clot strength parameters (all p &lt; 0.001) between both devices.Conclusions: Several parameters obtained by ClotPro show strong correlations with ROTEM Delta. Due to weak correlations of intrinsically activated clotting times and considerable absolute differences in a number of parameters, our findings underline the need for device-specific algorithms in this patient cohort.

Enhancing Appropriate Utilization of Coagulation Tests at St. Michael's Hospital

Blood ◽  
2016 ◽  
Vol 128 (22) ◽  
pp. 5922-5922
Author(s):  
Amy Skitch ◽  
Natalya E O'Neill ◽  
Aziz Jiwajee ◽  
Hina Chaudhry ◽  
Michael Fralick ◽  
...  
Keyword(s):  
Rate Ratio ◽  
Cost Savings ◽  
Coagulation Test ◽  
Educational Materials ◽  
Process Change ◽  
Simple Process ◽  
Institutional Level ◽  
Coagulation Testing ◽  
Coagulation Tests ◽  
Unnecessary Testing

Abstract Introduction and Objective The activated partial thromboplastin time (aPTT) and prothrombin time/ international normalized ratio (PT/INR) are the most commonly used coagulation tests (Chee et al 2008) and have become ubiquitous in medical practice despite only having been validated for very specific clinical indications (Capoor et al 2015, Pilsczek et al 2005). Indiscriminate use of these tests increases costs with little anticipated benefit for patients, and reliance on these test results to predict bleed risk may mislead care (Chee et al 2008). While staff education and development of revised practice guidelines may reduce unnecessary testing (Shojania & Grimshaw 2005), a simple process change to order panels has been shown to be associated with meaningful reductions in coagulation testing and associated costs without obvious adverse effects (Merkeley et al 2016). A prospective quality improvement initiative was conducted in the Emergency Department (ED) at St. Michael's Hospital in Toronto Canada. The ED was targeted as this was an area where coagulation test volumes were particularly high. The following strategies were implemented in order to enhance appropriate utilization of coagulation tests: PT/PTT testing options were uncoupled, ED order panels were revised, and educational materials were distributed to relevant stakeholders. These simple process changes resulted in significant reductions in unnecessary testing and meaningful cost savings. Weekly rates of PT/INR testing and aPTT per 100 ED patients decreased (17.2 vs. 38.4, rate ratio=0.45 (95% CI 0.43-0.47), p<0.001; 16.6 vs. 37.8, rate ratio=0.44 (95% CI 0.42-0.46), p<0.001, respectively). This decrease in coagulation testing was associated with $CAN 6,000 in direct cost savings per month and a one-year projected savings of $55,000. This intervention focused on one area in our institution, and its success highlights how a simple process change, when implemented with educational supports, can reduce unnecessary testing. We will now broaden this initiative to other departments in our institution where high coagulation test volumes occur. We aim to enhance appropriate utilization of coagulation testing and reduce associated expenditures at an institutional level. Materials and Methods We identified three additional departments at St. Michael's Hospital where coagulation test volumes are high: Inpatient wards, outpatient clinics, and the preoperative clinic. Stakeholders in each department were identified, and department-specific change strategies were developed the in outpatient and preoperative clinics thus far. Educational sessions were held and educational materials/prompts were developed for healthcare staff in these areas. Modifications to the preoperative clinic orders sets are currently under review. Results Similar to the ED, the main outcomes are aPTT/PT test volumes and costs. Same day alternate test volumes and perioperative blood transfusions (for the preoperative clinic and inpatient wards) are balance measures. Process control charting will be used to track utilization. We plan to monitor knowledge and attitudes through focus groups and surveys. The process for changes to order sets varies by department and we believe this process change to be imperative for maximum benefit. We will be sharing our change strategy and educational materials across all hospital departments in a priority sequence. Preliminary utilization data will also be presented. Comparisons will be made both within and between departments. Conclusions Changing aPTT/PT usage is a challenge due to the plethora of stakeholders involved; however, success achieved in the ED is expected to be a predictor of success in other departments within our institution. Clinicians in the inpatient, outpatient and preoperative clinics have acknowledged the history of unnecessary testing and have demonstrated a keen willingness to address this issue. Laboratory data has facilitated the identification of areas where there appears to be substantial overuse. We anticipate that our project will result in an important decrease in aPTT/PT utilization and associated expenditures at an institutional level with no evidence of harm. Lessons learned and educational materials will be shared with the hope of reducing indiscriminate coagulation testing on a larger scale. Disclosures Sholzberg: Shire (previously Baxter, Baxalta): Honoraria, Research Funding; Novonordisk: Honoraria.

scholarly journals Use of an Automated Coagulation Analyzer to Perform Heparin Neutralization With Polybrene in Blood Samples for Routine Coagulation Testing: Practical, Rapid, and Inexpensive

2013 ◽  
Vol 137 (11) ◽  
pp. 1641-1647 ◽  
Author(s):  
Panutsaya Tientadakul ◽  
Chulalak Kongkan ◽  
Wimol Chinswangwatanakul
Keyword(s):  
Prothrombin Time ◽  
Blood Samples ◽  
Coagulation Testing ◽  
Coagulation Tests ◽  
Clinically Significant ◽  
Aptt Reagent ◽  
Heparin Neutralization ◽  
Coagulation Analyzer ◽  
Suitable Sequence ◽  
Routine Coagulation

Context.—Heparin contamination in blood samples may cause false prolongation of activated partial thromboplastin time (aPTT) and prothrombin time results. Polybrene can neutralize heparin, but it affects coagulation by itself. Objectives.——To determine the optimal concentration of polybrene to neutralize heparin, to determine the suitable sequence of reagents for the neutralization method performed on the analyzer at the same time as prothrombin time and aPTT testing, and to detect the heparin contamination in blood samples for coagulation tests in our hospital using this method. Design.—Various concentrations of heparin were added to 10 normal and 76 abnormal plasma samples to study the efficacy of polybrene. Two programs of reagent sequencing for aPTT with polybrene performed on the analyzer were tested. Samples suspected of heparin contamination according to our criteria were selected for neutralization during a 3-month period. Results.——The optimal final concentration of polybrene was 25 μg/mL. Polybrene should be added after the aPTT reagent to minimize its interference effect. Even though results of prothrombin time and aPTT after neutralization did not equal those before the spike of heparin, the differences might not be clinically significant. Eighty-one of 4921 samples (1.6%) were selected for aPTT with the neutralization method, and the detection rate of heparin contamination was 84% (68 of 81), giving an overall incidence of 1.4% (68 of 4921). Conclusions.—This method is inexpensive and can be performed rapidly with prothrombin time and aPTT on the automated analyzer, which makes it easy to practice with no need for extra plasma volumes.

Prothrombin Time Standardization: Report of the Expert Panel on Oral Anticoagulant Control

1979 ◽  
Vol 42 (04) ◽  
pp. 1073-1114 ◽  
Keyword(s):  
Prothrombin Time ◽  
Expert Panel ◽  
The Other ◽  
Rabbit Brain ◽  
Calibration Constant ◽  
Freeze Dried ◽  
The Mean ◽  
Point Of Intersection ◽  
And Control ◽  
Standardization Report

SummaryIn collaborative experiments in 199 laboratories, nine commercial thromboplastins, four thromboplastins held by the National Institute for Biological Standards and Control (NIBS & C), London and the British Comparative Thromboplastin were tested on fresh normal and coumarin plasmas, and on three series of freeze-dried plasmas. One of these was made from coumarin plasmas and the other two were prepared from normal plasmas; in each series, one plasma was normal and the other two represented different degrees of coumarin defect.Each thromboplastin was calibrated against NIBS&C rabbit brain 70/178, from the slope of the line joining the origin to the point of intersection of the mean ratios of coumarin/normal prothrombin times when the ratios obtained with the two thromboplastins on the same fresh plasmas were plotted against each other. From previous evidence, the slopes were calculated which would have been obtained against the NIBS&C “research standard” thromboplastin 67/40, and termed the “calibration constant” of each thromboplastin. Values obtained from the freeze-dried coumarin plasmas gave generally similar results to those from fresh plasmas for all thromboplastins, whereas values from the artificial plasmas agreed with those from fresh plasmas only when similar thromboplastins were being compared.Taking into account the slopes of the calibration lines and the variation between laboratories, precision in obtaining a patient’s prothrombin time was similar for all thromboplastins.

scholarly journals Ex vivo evaluation of a multilayered sealant patch for watertight dural closure: cranial and spinal models

2021 ◽  
Vol 32 (8) ◽  
Author(s):  
A. Kinaci ◽  
S. van Thoor ◽  
S. Redegeld ◽  
M. Tooren ◽  
T. P. C. van Doormaal
Keyword(s):  
Ex Vivo ◽  
Resistance Test ◽  
Burst Pressure ◽  
Cerebrospinal Fluid Leakage ◽  
Computer Assisted ◽  
Dural Defect ◽  
Test Results ◽  
Physiological Conditions ◽  
Dural Attachment ◽  
The Mean

AbstractCerebrospinal fluid leakage is a frequent complication after cranial and spinal surgery. To prevent this complication and seal the dura watertight, we developed Liqoseal, a dural sealant patch comprising a watertight polyesterurethane layer and an adhesive layer consisting of poly(DL-lactide-co-ε-caprolactone) copolymer and multiarmed N-hydroxylsuccinimide functionalized polyethylene glycol. We compared acute burst pressure and resistance to physiological conditions for 72 h of Liqoseal, Adherus, Duraseal, Tachosil, and Tisseel using computer-assisted models and fresh porcine dura. The mean acute burst pressure of Liqoseal in the cranial model (145 ± 39 mmHg) was higher than that of Adherus (87 ± 47 mmHg), Duraseal (51 ± 42 mmHg) and Tachosil (71 ± 16 mmHg). Under physiological conditions, cranial model resistance test results showed that 2 of 3 Liqoseal sealants maintained dural attachment during 72 hours as opposed to 3 of 3 for Adherus and Duraseal and 0 of 3 for Tachosil. The mean burst pressure of Liqoseal in the spinal model (233 ± 81 mmHg) was higher than that of Tachosil (123 ± 63 mmHg) and Tisseel (23 ± 16 mmHg). Under physiological conditions, spinal model resistance test results showed that 2 of 3 Liqoseal sealants maintained dural attachment for 72 hours as opposed to 3 of 3 for Adherus and 0 of 3 for Duraseal and Tachosil. This novel study showed that Liqoseal is capable of achieving a strong watertight seal over a dural defect in ex vivo models.

Validity of hearTest Smartphone-Based Audiometry for Hearing Screening in Workers Exposed to Noise

2020 ◽  
Author(s):  
Luma Cordeiro Rodrigues ◽  
Silvia Ferrite ◽  
Ana Paula Corona
Keyword(s):  
Hearing Loss ◽  
High Specificity ◽  
Hearing Screening ◽  
Youden Index ◽  
Hearing Level ◽  
Predictive Values ◽  
Auditory Thresholds ◽  
The Mean ◽  
Low Sensitivity ◽  
Sensitivity Specificity

Abstract Purpose This article investigates the validity of a smartphone-based audiometry for hearing screening to identify hearing loss in workers exposed to noise. Research Design This is a validation study comparing hearing screening with the hearTest to conventional audiometry. The study population included all workers who attended the Brazilian Social Service of Industry to undergo periodic examinations. Sensitivity, specificity, the Youden index, and positive (PPV) and negative predictive values (NPV) for hearing screening obtained by the hearTest were estimated according to three definitions of hearing loss: any threshold greater than 25 dB hearing level (HL), the mean auditory thresholds for 0.5, 1, 2, and 4 kHz greater than 25 dB HL, and the mean thresholds for 3, 4, and 6 kHz greater than 25 dB HL. Note that 95% confidence intervals were calculated for all measurements. Results A total of 232 workers participated in the study. Hearing screening with the hearTest presented good sensitivity (93.8%), specificity (83.9%), and Youden index (77.7%) values, a NPV (97.2%), and a low PPV (69.0%) for the identification of hearing loss defined as any auditory threshold greater than 25 dB HL. For the other definitions of hearing loss, we observed high specificity, PPV and NPV, as well as low sensitivity and Youden index. Conclusion The hearTest is an accurate hearing screening tool to identify hearing loss in workers exposed to noise, including those with noise-induced hearing loss, although it does not replace conventional audiometry.

scholarly journals Distances between mandibular posterior teeth and the WALA ridge in Peruvians with normal occlusion

2017 ◽  
Vol 22 (6) ◽  
pp. 56-60 ◽  
Author(s):  
Carla Y. Kong-Zárate ◽  
Marcos J. Carruitero ◽  
Will A. Andrews
Keyword(s):  
Age Groups ◽  
Test Results ◽  
Posterior Teeth ◽  
Normal Occlusion ◽  
Tooth Type ◽  
The Mean ◽  
Student’S T ◽  
Mandibular Posterior Teeth ◽  
Digital Caliper ◽  
Student’S T Test

ABSTRACT Objective: The purposes of this investigation were to determine the horizontal distances between the mandibular posterior teeth and the WALA ridge in a sample of Peruvians with normal occlusion and to compare them by tooth type, sex, arch side, and age groups. Methods: 65 dental casts of subjects with normal occlusion were collected. Posterior teeth, except for third molars, were evaluated. The horizontal distances between the occluso-gingival midpoints of the buccal surfaces (FA points) of each tooth and the WALA ridge were measured using a modified digital caliper. The values between each different tooth type within the sample were compared using the ANOVA and Scheffe tests, while comparisons by sex, arch side and age groups, using the Student’s t-test. Results: The mean distances in the sample was 0.96 mm for first premolars, 1.45 mm for second premolars, 2.12 mm for first molars and 2.55 mm for second molars. Statistically significant differences between each of the four tooth types were found. There were no significant differences found between sex, arch side and age groups. Conclusion: The horizontal distances between the mandibular posterior teeth and the WALA ridge increased progressively from the first premolars to the second molars in Peruvians with normal occlusion. The WALA ridge was a good landmark to evaluate the positions of posterior teeth in Peruvians with normal occlusion.

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