Chapter 7
The importance of quality tests

Assessment of test quality is an essential step in the interpretation strategy. A suboptimal quality result reported as a good quality result may result in misclassification and incorrect management of a patient. Some might say a lung function test that has been done poorly is worse than not having the test done at all.

Test quality may be impacted by patient-related factors and/or equipment-related/technical factors (Table 7.1).

Table 7.1 Examples of factors that affect test quality.

Patient related	Equipment/technical related
Patient cooperation	Lack of calibration
Patient coordination	Incorrect ambient conditions entered
Patient cognition	Poor linearity of analysers/flow sensors
Patient effort	Inaccurate/imprecise devices
Language barriers	Drift
Pain	Leak
Inability to meet test acceptability criteria	Operator-related issues
Inability to meet test repeatability criteria	Lack of knowledge of acceptability and repeatability criteria Unable to elicit a maximal effort from subject Poor attention to detail with respect to inspection of individual efforts Poor feedback provided to patients on how to improve test quality

Assessment of test quality depends on the following:

Ability and skills of test operator
Accurate technical comments regarding test quality from test operator
Reporter’s knowledge of the principles of test measurement
Reporter’s knowledge of the impact of suboptimal quality test on interpretation of results

The test operator’s role in test quality includes the following:

Ensuring the equipment is calibrated and performing within its specifications
Having a sound knowledge of the test methodologies and the within-test acceptability and repeatability criteria
Providing instruction to the subject to elicit maximal effort, inspecting the raw data for acceptability and repeatability criteria and providing feedback to the subject to maximise test quality
Knowledge of between-test quality indicators
Documenting the test quality and specific factors that may affect test quality, often referred to as a technical comment. To promote consistency between test operators, some laboratories use quality rating scales (Table 7.2) (1, 2).

Table 7.2 An example of a spirometry quality rating scale (1,2).

Rating	Description	Interpretation
Good	3 acceptable efforts AND, of these acceptable efforts:	Good representation of the patient’s true lung function
	Best two FEV₁s match to within 150 mL AND Best two FVCs match to within 150 mL
Fairly good	2 acceptable efforts AND, of these acceptable efforts:	Fairly good representation of the patient’s true lung function
	Best two FEV₁s match to within 150 mL AND Best two FVCs match to within 150 mL
Fair	≥2 acceptable efforts AND, of these acceptable efforts:	Fair representation of the patient’s true lung function—interpret using some caution
	Best two FEV₁s are not within 150 mL OR Best two FVCs are not within 150 mL
Fairly poor	Only one acceptable test	Use caution in interpretation of the results—not satisfied that results are representative of the patient’s true lung function
Poor	No acceptable tests	Interpretation of the results is probably not possible, but may be able to say, for example, ‘VC is at least …’

The reporter’s role in assessment of test quality includes the following:

Inspection of raw data and/or inspection of technical comments
Understanding the principles of measurement
Understanding the within-test quality factors (see test-specific chapters for details)
Knowledge of between-test quality indicatorsSome simple between-test indicators of good quality (spirometry, T_LCO, static lung volumes) include the following:
- The inspiratory vital capacity (IVC) (from T_LCO) should be within 85% of the maximum vital capacity (VC) measured. If IVC < 85% of maximum VC, this may impact on V_A and T_LCO (see Case 5).
- The slow vital capacity (SVC) measured as part of static lung volumes (total lung capacity (TLC)-residual volume (RV)) should be greater than FVC-150 mL. This is a check of repeatability—that the SVC and the FVC are similar. In individuals with significant airflow limitation, SVC ≫ FVC, but it is unusual for FVC ≫ SVC, and when seen, this often reflects suboptimal test performance or technical issues (see Case 4).
- The TLC-RV should be greater than V_I (from T_LCO)-150 mL. As for the point earlier, this is a check of repeatability.
- The TLC should be greater than V_A (from T_LCO), especially in patients with airflow obstruction. Because of differences between devices and test methodologies, V_A may occasionally be just larger than TLC. However, if V_A is markedly higher than TLC, test performance or technical issues should be considered.
Identifying the impact of suboptimal quality tests on interpretation of results in the report.

To report or not to report suboptimal quality tests?

Although tests of good quality are said to provide a good representation of a patient’s true lung function, tests of suboptimal quality may not.

Sometimes, no test results are better than providing suboptimal test results that may lead to misclassification. However, some aspects of a suboptimal quality result may provide useful information that is worth reporting.

For example: A patient with cognitive impairment has difficulties producing maximal expiratory efforts during a spirometry test. The patient is unable to blow fast, but seems to be blowing from TLC to RV. As the patient is not blowing maximally, the FEV₁ reported is unlikely to be a true FEV₁ (as the manoeuvre is not forced), so it should not be reported. However, the total volume exhaled indicates that the VC is at least a certain amount.

If considering using tests of suboptimal quality, then consider the following:

The risk of misclassification
The impact of the quality on the interpretation

Use cautionary statements in the report to make it clear to the reader that there is an issue that may impact the interpretation. If you are able to determine the size and direction of the impact, then this should also be noted.

Examples of assessment of test quality

Steps in assessing test quality:

Read technical comment
Perform the simple between-test assessments of quality described earlier
Inspect raw data if able or where necessary
Evaluate impact of suboptimal quality on interpretation of results
Include a statement regarding test quality in the report based on the evidence
Where suboptimal quality is present—the statement should be cautionary and describe the impact of the issue on the interpretation of results.

Case 1

Technical comment:	Test performance was fairly poor. Poor technique, glottic interference, tongue occluding mouthpiece, back extrapolation error. FVC likely to be underestimated. FEV₁ may be impacted.
Cautionary statements:	Results should be interpreted with caution as test performance was fairly poor with FEV₁ and FVC likely to be underestimated.
Technical interpretation:	Despite the fairly poor test performance, baseline spirometry appears to be within normal limits.
Clinical context:

Final report: Results should be interpreted with caution as test performance was fairly poor with FEV₁, and FVC was likely to be underestimated. Despite this, baseline spirometry appears to be within normal limits.

Commentary: The superimposed flow–volume loops show the lack of acceptability and repeatability of the results. Some efforts lack maximal effort; others appear to have artefact related to tongue occluding the mouthpiece and glottic interference with early termination. There is concern about whether the FEV₁ is accurate, and the FVC is probably underestimated. The VC from an effort with a submaximal start provides the largest VC value and has been quoted as such. Although we are unable to be certain that the results are an accurate reflection of the patient’s true lung function, the results appear to be within normal limits and this is useful information for the referring physician. It should also be noted that no clinical context is provided in this case due to the uncertainty in the results.

Case 2

Gender:	Female
Age (yr):	20	Weight (kg):	65.8
Height (cm):	157.5	Race:	Caucasian
Clinical notes:	Asthma.
	Normal range	Baseline	z-score	Post-bronchodilator(BD)	Change (%)
Spirometry
FEV₁ (L)	>2.59
FVC (L)	>2.89
VC (L)	>2.89	2.55	−2.51	2.53	−2.56
FEV₁/(F)VC (%)	>77

Cautionary statements:	Results should be interpreted with caution as test performance was fairly poor. FEV₁ and FVC not quoted as likely to have been impacted by glottic interference (underestimated). Post-bronchodilator spirometry had similar pattern.
Technical interpretation:	The VC appears to be reduced; however, this may be underestimated due to test performance. The loop shape does not appear to show evidence of obstruction.
Clinical context:

Final report: Results should be interpreted with caution as test performance was fairly poor. FEV₁ and FVC not quoted as they are likely to have been underestimated due to glottic interference. The VC appears to be reduced; however, this may be underestimated due to test performance. Static lung volumes may assist with confirming restriction. The loop shape does not appear to show evidence of obstruction.

Commentary: The flow volume loops shown here represent the baseline efforts. Although the beginning of each effort meets start of test acceptability criteria, glottic interference leads to a disruption to airflow and affects FEV₁ and probably FVC. The best FVC has been quoted as the VC, as this provides some information. The shape of the flow volume curve does not suggest airflow limitation related to asthma, though there is obstruction related to glottic interference. It is difficult to provide a clinical context when test performance is submaximal.

Case 3

Cautionary statements:	Results should be interpreted with caution as baseline FVC is not repeatable, though this would not necessarily impact on overall results. Chest tightness noted by patient during baseline tests.
Technical interpretation:	There is an obstructive ventilatory defect with a reduced FVC. The response to inhaled bronchodilator is not significant, but returns FVC to within the normal range, suggesting FVC is possibly reduced due to airflow limitation. Static lung volumes could be performed to further elucidate results.
Clinical context:	Results are consistent with the spirometric definition of COPD.

Final report: Results should be interpreted with caution as baseline FVC is not repeatable, although the impact on overall results is likely to be small. There appears to be an obstructive ventilatory defect with a reduced FVC. The response to inhaled bronchodilator is not significant, but returns FVC to within the normal range, suggesting FVC is probably reduced due to airflow limitation. Static lung volumes could be performed to further elucidate results. Results are consistent with the spirometric definition of COPD.

Commentary: The flow volume loops shown here represent the baseline efforts. Although the baseline FVC is not repeatable, that is, the highest and second highest FVC from acceptable baseline efforts are more than 150 mL apart, the impact on the overall results is likely to be small. There was no significant increase in FVC with bronchodilator (though results come to within normal limits) and post-bronchodilator FVC results are repeatable, suggesting that the highest recorded FVC from baseline efforts was probably a close reflection of true lung function. Results with poor repeatability should not be excluded from reports and interpretation (3), but the person undertaking the interpretation needs to determine the impact of the lack of repeatability.

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Tags: Interpreting Lung Function Tests

Aug 21, 2016 | Posted by admin in RESPIRATORY | Comments Off

Gender:	Male
Age (yr):	60	Weight (kg):	78.8
Height (cm):	173.5	Race:	Caucasian
Clinical notes:	Chronic cough. ?COPD
	Normal range	Baseline	z-score	Post-BD	Change (%)
Spirometry
FEV₁ (L)	>2.65	1.55	−4.05	1.70	+10
FVC (L)	>3.60	3.47	−1.89	3.64	+5
FEV₁/(F)VC (%)	>66	45	−5.27	47
Technical comment:		Test performance was fair. Baseline FVC not repeatable—patient complained of chest tightness. Post-bronchodilator values repeatable.

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The importance of quality tests

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