Scottish Bowel Screening Programme colonoscopy quality - scope for improvement?

AIM

The delivery of the Scottish Bowel Screening Programme (SBoSP) is rooted in the provision of a high quality, effective and participant-centred service. Safe and effective colonoscopy forms an integral part of the process. Additional accreditation as part of a multi-faceted programme for participating colonoscopists, as in England, does not exist in Scotland. This study aimed to describe the quality of colonoscopy in the SBoSP and compare this to the English national screening standards.

METHODS

Data were collected from the SBoSP between 2007 and 2014. End-points for analysis were caecal intubation, cancer, polyp and adenoma detection, and complications. Overall results were compared with 2012 published English national standards for screening and outcomes from 2006 to 2009.

RESULTS

During the study period 53 332 participants attended for colonoscopy. The colonoscopy completion rate was 95.6% overall. The mean cancer detection rate was 7.1%, the polyp detection rate was 45.7% and the adenoma detection rate was 35.5%. The overall complication rate was 0.47%.

CONCLUSION

Colonoscopy quality in the SBoSP has exceeded the standard set for screening colonoscopy in England, despite not adopting a multi-faceted programme for screening colonoscopy. However, the overall adenoma detection rate in Scotland was 9.1% lower than that in England which has implications for colonoscopy quality and may have an impact on cancer prevention rates, a key aim of the SBoSP.

Participation in bowel screening among men attending abdominal aortic aneurysm screening

BACKGROUND

Uptake of population-based screening for colorectal cancer in Scotland is around 55 per cent. Abdominal aortic aneurysm (AAA) screening has recently been introduced for men aged 65 years and the reported uptake is 78 per cent. The aim was to determine the impact of a brief intervention on bowel screening in men who attended AAA screening, but previously failed to complete bowel screening.

METHODS

Men invited for AAA screening between September 2015 and March 2016 within NHS Tayside were included. Attendees who had not responded to their latest bowel screening invitation were seen by a colorectal cancer clinical nurse specialist. Reasons for not completing the faecal occult blood test (FOBT) were recorded; brief information on colorectal cancer screening was communicated, and participants were offered a further invitation to complete a FOBT. Those who responded positively were sent a further FOBT from the Scottish Bowel Screening Centre. Subsequent return of a completed FOBT within 6 months was recorded.

RESULTS

A total of 556 men were invited for AAA screening, of whom 38·1 per cent had not completed a recent FOBT. The primary reason stated for not participating was the time taken to complete the test or forgetting it (35·1 per cent). Other reasons included: lack of motivation (23·4 per cent), confusion regarding the aim of screening (16·2 per cent), disgust (19·8 per cent), fear (6·3 per cent) and other health problems (9·9 per cent). Following discussion, 81·1 per cent agreed to complete the FOBT and 49 per cent subsequently returned the test.

CONCLUSION

A substantial proportion of previous bowel screening non-responders subsequently returned a completed FOBT following a brief intervention with a nurse specialist. Attendance at non-bowel screening appointments may provide a valuable opportunity to improve bowel screening uptake.

Patterns of uptake in a biennial faecal occult blood test screening programme for colorectal cancer

AIM

The patterns of response in faecal occult blood test (FOBT) screening were studied.

METHOD

A total of 251,578 people invited three times for faecal occult blood testing were categorized according to how they responded to the invitations, as follows: YNN, NYN, NNY, NYY, YNY, YYN, YYY or NNN (Y = response; N = no response).

RESULTS

Overall, 163,038 (64.8%) responded at least once, and of those the biggest category was YYY (98,494, 60.4%). Of 1927 cancers diagnosed in the age group eligible for screening, there were 405 screen-detected cancers, 529 interval cancers and 993 cancers arising in people who had not been screened for over 2 years (i.e. falling outside the interval cancer category). In the YYY group, 79 screen-detected cancers would have been missed had the members of this group responded YNN and 65 had they responded YYN. In the YYN group, 104 screening cancers would have been missed if they had followed the YNN pattern. In most cases, the screen-detected cancers were diagnosed at the last invitation accepted, indicating that, after a diagnosis of cancer, further screening invitations were rarely accepted. Accordingly, the numbers of screen-detected and interval cancers were adjusted for likely pattern of response according to the proportion of the whole population falling into each pattern. With this adjustment, 40.9% of the cancers in the YYY group were screen detected compared with 29.3% in the YYN group and 20.7% in the YNN group (P < 0.001). Among those who responded once, twice and three times, the stage distribution of screen-detected cancers was similar, indicating that the prognosis of screen-detected cancer is unlikely to be poorer if not detected at the first screen.

CONCLUSION

This study is the first to examine patterns of response to screening invitations and confirms the importance to individuals of continuing to accept repeated screening invitations.

Low faecal haemoglobin concentration potentially rules out significant colorectal disease

AIM

The study aimed to determine whether faecal haemoglobin (Hb) concentration can assist in deciding who with lower abdominal symptoms will benefit from endoscopy.

METHOD

Faecal Hb concentrations were measured on single samples from 280 patients referred for lower gastrointestinal tract endoscopy from primary care in NHS Tayside who completed a faecal immunochemical test (FIT) for Hb and underwent subsequent endoscopy.

RESULTS

Among 739 invited patients, FIT and endoscopy were completed by 280 (median age 63 (18-84) years; 59.6% women), with a median time between FIT and endoscopy of 9 days. Six (2.1%) participants had cancer, 23 (8.2%) had high-risk adenoma (HRA) (more than three adenomas or any > 1 cm), 31 (11.1%) low-risk adenoma (LRA) and 26 (9.3%) inflammatory bowel disease (IBD) as the most serious diagnosis. Those with cancer had a median faecal Hb of > 1000 ng Hb/ml buffer. Those with cancer + HRA + IBD had a median faecal Hb concentration of 75 ng Hb/ml buffer (95% CI 18-204), which was significantly higher than that of all remaining participants without significant colorectal disease (P < 0.0001). Using a cut-off faecal Hb concentration of 50 ng Hb/ml buffer, negative predictive values of 100.0%, 94.4%, 93.4% and 93.9% were found for cancer, HRA, LRA and IBD. Patients with reasons for referral other than rectal bleeding and family history did not have high faecal Hb concentrations.

CONCLUSION

Faecal Hb concentration measurements have considerable potential to contribute to reducing unnecessary endoscopy for the majority of symptomatic patients.

Negative screening colonoscopy after a positive guaiac faecal occult blood test: not a contraindication to continued screening

AIM

In guaiac faecal occult blood test (gFOBT) screening at least 50% of positive individuals will have a colonoscopy negative for colorectal neoplasia. The question of continuing screening in this group has not been addressed.

METHOD

Data on participants aged 50-69 years with a positive gFOBT result and a negative colonoscopy were followed through the biennial screening pilot conducted between 2000 and 2007 in Scotland.

RESULTS

In the first screening round, 1527 colonoscopies were negative for neoplasia. 1300 were re-invited in the second round, 905 accepted, and 157 had a positive gFOBT result, giving a positivity rate of 17.4%. Colonoscopy revealed 20 subjects with adenoma and six with invasive cancer. In the third screening round 1031 were invited for a third time and 730 accepted: 55 had a positive gFOBT test, giving a positivity rate of 7.5%. In this group, six colonoscopies revealed adenomas but there were no cancers diagnosed. In the third screening round, 108 individuals had had two positive gFOBT results and two subsequent negative colonoscopies. Eighty-four were invited for a third gFOBT, 66 accepted and 19 (25.6%) had a positive result none of whom had an adenoma or carcinoma.

CONCLUSION

These data indicate that a negative colonoscopy following a positive gFOBT is not a contraindication for further screening, although this is likely to have a low yield of neoplastic pathology after two negative colonoscopies.

The impact of population-based faecal occult blood test screening on colorectal cancer mortality: a matched cohort study

Background:

Randomised trials show reduced colorectal cancer (CRC) mortality with faecal occult blood testing (FOBT). This outcome is now examined in a routine, population-based, screening programme.

Methods:

Three biennial rounds of the UK CRC screening pilot were completed in Scotland (2000–2007) before the roll out of a national programme. All residents (50–69 years) in the three pilot Health Boards were invited for screening. They received a FOBT test by post to complete at home and return for analysis. Positive tests were followed up with colonoscopy. Controls, selected from non-pilot Health Boards, were matched by age, gender, and deprivation and assigned the invitation date of matched invitee. Follow-up was from invitation date to 31 December 2009 or date of death if earlier.

Results:

There were 379 655 people in each group (median age 55.6 years, 51.6% male). Participation was 60.6%. There were 961 (0.25%) CRC deaths in invitees, 1056 (0.28%) in controls, rate ratio (RR) 0.90 (95% confidence interval (CI) 0.83–0.99) overall and 0.73 (95% CI 0.65–0.82) for participants. Non-participants had increased CRC mortality compared with controls, RR 1.21 (95% CI 1.06–1.38).

Conclusion:

There was a 10% relative reduction in CRC mortality in a routine screening programme, rising to 27% in participants.

Interval cancers in a FOBT-based colorectal cancer population screening programme: implications for stage, gender and tumour site

BACKGROUND

Between 2000 and 2007, a demonstration pilot of biennial guaiac faecal occult blood test (GFOBT) screening was carried out in Scotland.

METHODS

Interval cancers were defined as cancers diagnosed within 2 years (ie, a complete screening round) of a negative GFOBT. The stage and outcome of the interval cancers were compared with those arising contemporaneously in the non-screened Scottish population. In addition, the gender and site distributions of the interval cancers were compared with those in the screen-detected group and the non-screened population.

RESULTS

Of the cancers diagnosed in the screened population, interval cancers comprised 31.2% in the first round, 47.7% in the second, and 58.9% in the third, although this was due to a decline in the numbers of screen-detected cancers rather than an increase in interval cancers. There were no consistent differences in the stage distribution of interval cancers and cancers from the non-screened population, and, in all three rounds, both overall and cancer-specific survival were significantly better for patients diagnosed with interval cancers (p<0.01). The percentage of cancers arising in women was significantly higher in the interval cancer group (50.2%) than in either the screen-detected group (35.3%, p<0.001) or the non-screened group (40.6%, p<0.001). In addition, the proportion of both right-sided and rectal cancers was significantly higher in the interval cancer group than in either the screen-detected (p<0.001) or non-screened (p<0.004) groups.

CONCLUSIONS

Although GFOBT screening is associated with substantial interval cancer rates that increase with screening round, the absolute numbers do not. Interval cancers are associated with a better prognosis than cancers arising in a non-screened population, and GFOBT appears to preferentially detect cancers in men and the left side of the colon at the expense of cancers in women and in the right colon and rectum.

Experience with a wipe guaiac-based faecal occult blood test as an alternative test in a bowel screening programme

The format of the traditional guaiac faecal occult blood test (gFOBT), particularly the collection technique, might cause difficulties for some. A multistage evaluation of alternative tests was performed. Firstly, four tests with different faecal collection approaches were assessed: a focus group recommended further investigation of a wipe gFOBT. Secondly, 100 faecal samples were analysed using two wipe tests and the routine gFOBT: no differences were found. Thirdly, a wipe gFOBT was introduced. Over 21 months, 400 requests were made and 311 wipe kit sets were submitted for analysis: 153 (49.2%) were negative, 21 (6.8%) positive (all 3 kits positive), 96 (30.9%) weak positive (1 or 2 positive) and 41 (13.2%) un-testable. Forty-three participants were referred for colonoscopy. Outcome data were provided on 39 participants: nine declined colonoscopy, two were judged unsuitable, two did not attend, two were already in follow-up, 13 had normal colonoscopy and two normal barium enema, two had diverticular disease, two had a metaplastic polyp, four had a low-risk adenoma and one had a high-risk adenoma. No participant had cancer. Detection of significant neoplasia was small. The use of the wipe gFOBT was ceased: it cannot be recommended as a screening test for bowel cancer.

Analytical goals for haematology tests

All analytical methods can be defined in terms of their practicability and reliability performance characteristics. Desirable standards of performance, or analytical goals, are required for these, particularly for imprecision and inaccuracy. Goals for imprecision have been set using a variety of methods including reference values, opinions of clinicians, views of individuals, and data on biological variation. The last approach is currently favoured; desirable imprecision is equal to or less than one-half of the biological within-subject variation. If this goal is met, total variability of test results is increased by less than about 10% due to analytical variability. Valid estimates of within-subject variability are available for the complete blood count. The goal for inaccuracy is that methods should have no bias so that results are comparable over time and geography; goals based on biological variation should be viewed and used, therefore, as goals for total error. In current practice, some of the goals cannot be met; they should be considered as targets worthy of achievement, not as inflexible criteria of acceptance or rejection of methods.

Results from the first three rounds of the Scottish demonstration pilot of FOBT screening for colorectal cancer

OBJECTIVES

To assess the effects of the first three rounds of a pilot colorectal screening programme based on guaiac faecal occult blood testing (gFOBT) and their implications for a national population-based programme.

METHODS

A demonstration pilot programme was conducted in three Scottish NHS Boards. Residents aged between 50 and 69 years registered on the Community Health Index were included in the study.

RESULTS

In the first round, the uptake was 55.0%, the positivity rate was 2.07% and the cancer detection rate was 2.1/1000 screened. In the second round, these were 53.0%, 1.90% and 1.2/1000, respectively, and in the third round, 55.3%, 1.16% and 0.7/1000, respectively. In the first round, the positive predictive value of the gFOBT was 12.0% for cancer and 36.5% for adenoma; these fell to 7.0% and 30.3% in the second round and were maintained at 7.5% and 29.1% in the third round. The percentage of screen-detected cancers diagnosed at Dukes' stage A was 49.2% in the first round, 40.1% in the second round and 36.3% in the third round.

CONCLUSIONS

These results are compatible with those of previous randomised trials done in research settings, demonstrating that population-based colorectal cancer screening is feasible in Scotland and should lead to a comparable reduction in disease-specific mortality.

Automated immunochemical quantitation of haemoglobin in faeces collected on cards for screening for colorectal cancer

BACKGROUND

Simple card collection systems are becoming available for faecal immunochemical tests (FITs) as well as guaiac faecal occult blood tests (gFOBTs). FITs are now obtainable that allow quantitation of haemoglobin, so that the analytical detection limit can be set to give a positivity rate that is manageable in terms of the available colonoscopy. A combination of a card collection device and an automated FIT analytical system could be advantageous.

METHODS

The quantitation of haemoglobin in samples collected on cards with a new analytical system and the relationship between faecal haemoglobin concentration and pathology were investigated in a cohort of gFOBT-positive individuals.

RESULTS

All groups had large ranges of haemoglobin concentration and there was overlap between the groups. Median haemoglobin concentrations in participants with normal findings on colonoscopy (167), diverticular disease (43), hyperplastic polyps (41), low risk adenoma (63), higher risk adenoma (35) and cancer (27) were 13.5, 15.6, 16.8, 15.2, 65.6 and 168.9 ng/ml haemoglobin, respectively. Those with diverticular disease, hyperplastic polyps and low risk adenoma were not significantly different from the normal group (p>0.2), but those with higher risk adenoma had significantly higher concentrations (p<0.001), as did those with cancer (p<0.001). Receiver operating characteristic analysis demonstrates that the cut-off concentration can be set to give appropriate clinical characteristics; optimum sensitivity and specificity are achieved at 26.7 ng/ml.

CONCLUSIONS

The haemoglobin in faeces on simple FIT card collection devices can be immunoturbidimetrically analysed quantitatively, and the concentration relates to the presence or absence of significant neoplastic disease.

The case of the floating gel

In patients with chronic renal failure, blood samples for laboratory analysis are often taken via dialysis catheters. This report describes a case of gross spurious hypernatraemia in a blood sample collected from a patient undergoing haemodialysis. After centrifugation of the blood sample in question, the separator gel formed the topmost layer, with the serum in the middle and the clot at the bottom. Subsequent analysis of the serum showed severe hypernatraemia (serum sodium, 744 mmol/litre). It was established that the blood sample had been taken from the patient's dialysis catheter into which 3 ml of Citra-Lock (46.7% trisodium citrate) had been instilled previously as a "catheter locking" solution. The hypernatraemia seen in this case was recognised immediately as an artefact, but it was found that even minimal contamination of blood samples with Citra-Lock may significantly affect sodium concentrations. This contamination may be missed, with potentially adverse consequences for patient management.

Green-coloured results on guaiac-based faecal occult blood testing should be considered positive

BACKGROUND

In guaiac-based faecal occult blood tests (FOBT), blue colours are considered positive. Blue-green colours should also be considered positive. Distinct green colours are said to be due to bile and it is stated that these should be interpreted as negative. The purpose of this study was to determine the clinical outcomes in individuals in whom the FOBT had difficult-to-interpret green colours that did not wash out on addition of developer.

METHODS

During the examination of 134 844 FOBT received in the Scottish laboratory in the first screening round of the UK Colorectal Cancer Screening Pilot, samples with green colour that did not wash out during development were identified. The clinical outcomes were determined from the comprehensive data set collected for each participant.

RESULTS

A small number (77) of FOBT were recorded as green-coloured on development. These were reported as positive and the usual investigation algorithm followed. Significant pathology was present in 31 of the 77 participants (40.3%). Negative outcomes encompassed 39 of the 77 participants (50.6%). The outcome could not be determined accurately for seven of the 77 participants (9.1%). Importantly, 17 of the participants (22.1%) had polyps.

CONCLUSIONS

Any green colour that does not wash out to the periphery of the guaiac tape on development of FOBT should be reported as a positive result, and manufacturers should clarify their instructions on interpretation.

Angiotensin converting enzyme activity in infancy is related to birth weight

AIMS

(a) To measure infant angiotensin converting enzyme (ACE) activity in healthy term infants at birth and during the first three months of life. (b) To determine the relation between serum ACE activity and infant feeding practice during this period. (c) To investigate the relation between serum ACE activity and birth weight and other potential contributing factors including acid-base status at birth, gestation, and maternal ACE genotype.

METHODS

Prospective study of term infants, with clinical and feeding data collected from parents and medical records, and serum ACE measured in the infant at birth and 1 and 3 months of age, and in the mother at the time of birth and one to three months after birth.

RESULTS

At birth and 1 and 3 months of age, infant serum ACE activity was twice that of maternal ACE activity. Infant ACE activity at birth and 1 and 3 months did not significantly differ between breast and formula fed infants. There was a highly significant negative correlation between infant ACE activity at 3 months and birth weight (r = -0.52; p < 0.001). This persisted after the conversion of birth weights to z scores (r = -0.34; p = 0.03). ACE activity at 3 months was also related to placental weight (r = -0.30; p = 0.02) and maternal age (r = -0.30; p = 0.05). The strong correlation between serum ACE activity and birth weight z score persisted after adjustment for maternal age and placental weight (r = -0.34; p = 0.03).

CONCLUSION

As ACE is increasingly identified as a risk factor for cardiovascular disease, serum ACE activity in infancy may contribute to the link between low birth weight and later cardiovascular events.

Optimal analytical performance for point of care testing

Quality specifications for the reliability of performance characteristics of laboratory testing, particularly precision and bias, are necessary prerequisites for creation and control of analytical quality. Many strategies have been promulgated for setting these specifications. Recently, the available approaches have been fixed into a hierarchical framework that has now been accepted by experts in the field to be the best current approach to a global strategy for setting quality specifications in laboratory medicine. They should be incorporated into quality planning strategies everywhere irrespective of the settings in which laboratory medicine is practised, including the point of care testing (POCT). Models higher in the hierarchy are preferred to lower approaches but lower approaches are better than none and should be used as the minimum standard.

Influence of index of individuality on false positives in repeated sampling from healthy individuals

The index of individuality is defined as the ratio of the within-subject biological variation to the between-subject variation, i.e., the variation between the biological set-points. It has been disputed whether the index of individuality has influence on the usefulness of conventional population-based reference intervals. In this investigation we found that, as long as only a single sample is taken, for a certain change in an individual's set-point, the index of individuality has no influence on the usefulness of reference intervals. When two or more samples are taken into account, however, the outcome of the measurement is highly dependent on the index of individuality. For a low index, repeat measurement has only limited effect on the fraction of false-positive results, as the next result will be close to the first, but, when the index is high, the fraction of false-positive results will be reduced considerably through repeating the test. Moreover, the distribution of biological set-points for which the fraction of false-positive results originate is described and the influence of analytical imprecision is discussed. The calculations are performed for values of the index of individuality from 0 to 2.0 for the traditional 95% reference interval based on x +/- 2*s(total) (s(total) = total biological variation), and also for a decision limit (cut-off point) x +/- 3*s(total). The numbers are, of course, different, but the effects of the index of individuality are the same, independent of the chosen cut-off point. This concept is related to the clinical classification (diagnosis, prognosis, screening) and the difference from different principles of monitoring is discussed. Further, five examples are evaluated and aspects of index of individuality in relation to false-positive results are discussed.

A model for setting analytical quality specifications and design of control for measurements on the ordinal scale

A model for characterization of measurements on the ordinal scale is presented. It is based on transformation of the calculated fractions (fractiles) of positives from measurements on samples with known concentrations to a probit-natural log (probit-ln) scale. Such measurements could be made by other methods on ratio or difference scales but, for convenience (for example for speed or low cost), are measured on the ordinal scale by "simple" methods. The model is examined, and verified, using three examples from published data (haemoglobin, glucose, and leukocytes) and an external quality assessment survey on measurements of streptococcus. We show that it is possible to obtain reliable analytical quality specifications and to establish design of control systems for measurements on the ordinal scale. It is concluded that the presented probit-ln model for the ordinal scale is a tool which can improve and facilitate (i) characterizing methods with measurements on the ordinal scale, (ii) defining analytical quality specifications, (iii) designing external assessment as well as internal control schemes, (iv) validation of methods with measurements on the ordinal scale according to the analytical quality specifications, and further, (v) reduction of the number of samples required for method validation and the number of replicate measurements needed.

General strategies to set quality specifications for reliability performance characteristics

Many strategies have been promulgated for the setting of quality specifications in laboratory medicine. Based on the analysis of the effect of error on clinical decision making, general quality specifications for precision, bias, the allowable difference between two analytical methods, drugs, fixed limits for use in external quality assessment and reference methods seem best derived from components of biological variation.

The index of individuality is often a misinterpreted quantity characteristic

The concept of the "index of individuality" was introduced by Eugene Harris in 1974. The index of individuality, calculated as (CV(A)2 + CV(I)2)(1/2)/CV(G), where CV(A), CV(I), and CV(G) are analytical, within-subject, and between-subject coefficients of variation respectively, has been used by many to investigate the utility of conventional population-based reference values. For a high index of individuality, > 1.4, it has been said that reference intervals will be more useful than for a low index, < 0.6. The validity of these concepts is investigated here and a number of our findings are at odds with the generally held opinion. The index of individuality has no impact on the fraction of individuals classified using population-based reference values, as long as the change in concentration from the usual state is of the same absolute magnitude and one sample is assayed to detect disease. However, when a measurement falling outside a reference limit is repeated in order to verify the finding, the index of individuality has considerable influence. For quantities with very low indices, the repeat test result, will be close to the first and give no new information, whereas for quantities with high indices, a repeat test will decrease the number of true positives and false positives.

Biological variation of cardiac markers: analytical and clinical considerations

The analytical, within-subject and between-subject components of variation were estimated for serum total creatine kinase (TCK) activity, CK-MB (creatine kinase-MB) activity, CK-MB mass, ratios of CK-MB activity and CK-MB mass to TCK activity and myoglobin concentration in a cohort of 16 apparently healthy subjects over 5 days. Analytical goals based on biological variation showed that, for all quantities except CK-MB mass, methodological improvement is warranted. All cardiac markers showed marked individuality which casts doubt on the utility of conventional population-based reference values as interpretative criteria. The critical differences required for significance of changes in serial results differ markedly from marker to marker and the data allow generation of objective criteria for monitoring individuals.

The influence of analytical bias on diagnostic misclassifications

Quality specifications for analytical imprecision and bias based on the state of the art; 'biology' and 'analysis of clinical situations' have been proposed by several scientists. Most interesting is the assessment of 'diagnostic misclassifications' based on direct evaluation of the consequences of analytical bias on the percentage of false positives and false negatives from a clinical decision situation, or based on the percentage of healthy individuals outside each reference limit when common reference intervals are used. With use of graphical or computer simulations assuming increasing (positive or negative) analytical bias, the expected percentage of misclassifications can be estimated- and, for the error for which the outcome (the fraction of misclassifications) is considered unacceptable, the maximum allowable analytical bias can be defined. An overview is given of previous proposals for specification of allowable analytical bias, and new examples are presented: (i) for S-transferrin. an analytical bias of +10% will increase the percentage of healthy individuals with measured concentration values above the upper reference limit from 2.5 to 10% (ii) the percentage of healthy men with concentration values for S-cholesterol above 6.2 mmol/l (240 mg/dl) will vary between 25 and 85% for analytical bias from - 1.0 to +1.0 mmol/l (+/- 16%): (iii) for glycated haemoglobin, two examples are given which illustrate the effect of analytical bias on the risk of retinopathy and so-called 'microalbuminuria' for measured values identical to the target 7.5% and 10.1% glycated haemoglobin, respectively. It is concluded that analytical bias may have significant impact on diagnostic performance, better standardization is needed, and quality specifications for allowable analytical bias should be based on medical usefulness criteria or, if such data are not available, on biological criteria.

Characterization and classification of external quality assessment schemes (EQA) according to objectives such as evaluation of method and participant bias and standard deviation. External Quality Assessment (EQA) Working Group A on Analytical Goals in Laboratory Medicine

Within the scope of this paper, the Working Group has attempted to place external quality assessment (EQA) within the whole context of quality management in laboratory medicine. First, the objectives of EQA schemes are defined and current EQA schemes evaluated. In most schemes, the objectives are not defined a priori and do not allow the definition of the origin of unacceptable individual results from participants. There is an ongoing trend for making traditional EQA schemes more interesting for the participants. Analysis of the factors involved in analytical quality allow the definition of the essential analytical tasks of educational EQA schemes. Beside these quality control tasks, educational EQA also includes quality assurance elements. EQA today has not only an important role to play in the assessment of each participant's performance but also in the assessment of the method. Efficiency of the schemes and educational impact can be improved by appropriate scheme designs according to objectives. After this theoretical approach, some practical examples of problem related EQA designs are given.

Serum tumor markers in monitoring patients: interpretation of results using analytical and biological variation

During cancer monitoring, data on biological and analytical variation are required in order to define the critical difference which provides an objective means to interpret serial values. We evaluated four tumor markers on serial samples collected from healthy subjects and patients. Analytical coefficients of variation (CV(A)), were obtained from "precision profiles" based on the differences between duplicates cumulated from assay runs in the laboratory. We defined the mean intrasubject biological variation (CV(I)) for CA 19-9 and TPA, separately for healthy people and patients; since the differences between the two groups were not statistically significant, we pooled the results and re-evaluated CV(I) in the combined groups (CA 19-9: CV(I) = 15.9%; TPA: CV(I) = 25.7%). In addition, we evaluated CV(I) for CEA (10.9%) and for TPS (25.9%) in patients. We then evaluated the inter-subject biological variations (CV(G)); the calculated indices of individuality for the four markers were less than 0.6 which shows conventional reference values to be of little utility for interpretation. We finally evaluated the critical differences (p < 0.05) for CA 19-9 (CD = 44.7%), for TPA (CD = 72.5%), CEA (CD = 32.7%) and TPS (CD = 72.5%); these are generally applicable since there was no heterogeneity in intra-subject biological variability.

Desirable performance standards for imprecision and bias in alternate sites. The views of laboratory professionals

Many strategies exist for the delineation of desirable performance standards for imprecision and inaccuracy (bias). All have disadvantages and advantages. Currently, the professional consensus is that the favored approach is based on biology: desirable imprecision is less than one half of the within-subject biological variation and desirable inaccuracy is less than one quarter of the group (within-subject plus between-subject) biological variation. Current laboratory performance allows these goals to be met for many quantities. In the past, analyses done at sites other than the laboratory achieved poorer results, but recent advances in technology appear to allow some biology-based goals, which in our view are the appropriate standards, to be met. Further advances in setting and widely promulgating goals, making good calibrants widely available, and developing quality control, assessment, and management are all required to ensure that the desirable performance standards are obtained in all locations in the future.

Desirable routine analytical goals for quantities assayed in serum. Discussion paper from the members of the external quality assessment (EQA) Working Group A on analytical goals in laboratory medicine

The aim of the Working Group was to describe guidelines for deriving desirable analytical goals in laboratory medicine. First, a literature review is given of the different approaches used until now, and some of the most important studies are presented in detail. These approaches are then discussed critically, and the analytical goals proposed by the group are outlined with respect to monitoring and diagnostic testing. The group recommends that, most realistically, analytical quality specifications be biologically based. For diagnostic testing, the aim is achievement of accuracy, allowing the use of common reference intervals when populations are homogeneous for a given quantity. For monitoring (within an individual laboratory and performed with the same instrument), analytical performance should aim at stable operation and low imprecision compared with the within-subject biological variation. Method accuracy is also very important for the comparability of results from different laboratories or instruments.

Acute effects of captopril on the renal actions of furosemide in patients with chronic heart failure

This study examined the effects of conventional doses of oral captopril on the renal responses to oral furosemide in ambulant patients with stable chronic heart failure. Twenty-five men (mean age 63 years) were randomized to one of two groups. Group 1 received placebo on days 1 and 2 before furosemide. Group 2 received placebo on day 1 before furosemide and captopril thereafter (i.e., captopril before furosemide on day 2). Urine was collected after either placebo or captopril and after furosemide (taken after placebo or captopril pretreatment). Captopril by itself did not affect renal function. Captopril did, however, significantly affect the renal response to furosemide. The increase in urine flow rate after furosemide in group 2 was decreased from 225% with placebo to 128% with captopril (p < 0.02). The increase in sodium excretion after furosemide was decreased from 623% with placebo to 242% with captopril (p < 0.001). Pretreatment with captopril abolished the increase in creatine clearance after furosemide. The increase in urinary albumin excretion (used as a marker of glomerular function) after furosemide was also significantly blunted by captopril. Conventional doses of captopril acutely inhibit the natriuretic and diuretic responses to furosemide at the glomerular level in ambulant patients with stable chronic heart failure.

Desirable standards for laboratory tests if they are to fulfill medical needs

Many strategies to define desirable standards for laboratory tests to fulfill medical needs have been proposed over the last three decades. Traditional approaches are based on reference (normal) values, opinions of clinicians, the state of the art, views of experts, data on biological variation, and assessment of the effect of error on clinical use. All these approaches have advantages and disadvantages, but the consensus of experts reached over a decade ago that imprecision desirably be less than one-half of the within-subject biological variation still seems to provide the best set of generally applicable performance standards. Desirable bias is less than one-quarter of the group (within-subject plus between-subject) biological variation. Recent proposals are either restatements of traditional recommendations, further empirical suggestions, or models based on assessment of clinical needs, and have not been widely accepted. Both old and new studies on clinical opinions, sought by using structured questionnaires containing clinical vignettes designed to seek views on the magnitude of significant change, are flawed in design, execution, and data analysis. Until clinicians are more aware of test-result variability and clinical chemists gain quantitative knowledge on the interpretation of test results, it will be difficult to set desirable standards that fulfill actual medical needs, except in a few well-defined screening situations.

Biological variation of acute phase proteins

The analytical, within-subject and between-subject components of variation were estimated for serum albumin, transthyretin, alpha 1-acid glycoprotein, alpha 1-antichymotrypsin, haptoglobin, beta 2-microglobulin and C-reactive protein in a cohort of 19 apparently healthy subjects over 20 weeks. Desirable analytical goals based on biological variation should be able to be met except for serum albumin and beta 2-microglobulin for which methodological improvement is warranted. All proteins showed marked individuality which casts doubt on the utility of conventional population-based reference values as interpretative criteria. The critical differences required for significance of changes in serial results differ markedly from protein to protein and the data presented allow generation of objective criteria for monitoring individuals.

Desirable standards for laboratory tests if they are to fulfill medical needs

Many strategies to define desirable standards for laboratory tests to fulfill medical needs have been proposed over the last three decades. Traditional approaches are based on reference (normal) values, opinions of clinicians, the state of the art, views of experts, data on biological variation, and assessment of the effect of error on clinical use. All these approaches have advantages and disadvantages, but the consensus of experts reached over a decade ago that imprecision desirably be less than one-half of the within-subject biological variation still seems to provide the best set of generally applicable performance standards. Desirable bias is less than one-quarter of the group (within-subject plus between-subject) biological variation. Recent proposals are either restatements of traditional recommendations, further empirical suggestions, or models based on assessment of clinical needs, and have not been widely accepted. Both old and new studies on clinical opinions, sought by using structured questionnaires containing clinical vignettes designed to seek views on the magnitude of significant change, are flawed in design, execution, and data analysis. Until clinicians are more aware of test-result variability and clinical chemists gain quantitative knowledge on the interpretation of test results, it will be difficult to set desirable standards that fulfill actual medical needs, except in a few well-defined screening situations.

Age-related changes in laboratory test results. Clinical implications

Many quantities assayed in clinical laboratories demonstrate age-related changes. Particularly important periods are early life, adolescence, old age, and after the menopause in females. The changes that occur until adulthood are well documented. Fewer data are available on elderly people even though they consume a large component of healthcare resources. In diagnosis, and prior to initiation of drug therapy, when no previous results are available, reference values must be available to aid interpretation. Reference intervals generated from elderly people are sometimes wider than in younger adults. It is suggested that conventional adult reference values should be used in general for the very elderly since, at least in part, the wider intervals are probably due to inclusion of individuals who are unhealthy in the reference sample group. Most quantities have marked individuality, and serial values for an individual span only a part of the reference interval. Individuals can have values which are very unusual for them but still lie within the reference limits; this implies that clinical laboratory tests will be less than ideal in the detection of latent or early disease. The average within-subject variation in healthy elderly people and younger adults is similar. Therefore, the large database on biological variation can be used, with analytical imprecision, to calculate critical differences for serial results in an elderly individual which must be exceeded before significance can be claimed. These critical differences are of value in monitoring the effects of drug therapy.