Chapter 8 When the results do not fit the rules
As you become more proficient at interpretation and report writing, and increase the volume of reports you are writing, you will come across the occasional case that does not easily fit accepted interpretation strategies. This adds complexity to report writing and increases uncertainty. How do we account for:
Borderline results? For example, a forced vital capacity (FVC) measured at 3.95 L with a lower limit of normal (LLN) of 4.00 L when all other parameters of spirometry are within normal limits. A response to inhaled bronchodilator (BD) that has a large absolute volume increase, but not a 12% increase? For example, an increase in FEV1 by 10% and 0.45 L in response to inhaled bronchodilator in an individual with known asthma. Errors associated with extrapolating reference equations? For example, an extrapolated reference value may suggest a result is within normal limits, but in fact, the absolute value is low and may impact on function. Lung function interpretation is not black and white, and there will be exceptions to the rules. Subjectivity, as discussed in Chapter 1, now comes into play. Often, it is the clinical background that brings context to allow a judgement to be made regarding normality or abnormality or change or no change. Sometimes, you may need to express your uncertainty in the significance of findings made. This last chapter focuses on cases that are not straightforward.
Case 1 Ms Ava X is a 39-year-old female who first presented for respiratory review 14 months prior to the current visit with breathlessness. After multiple investigations she was diagnosed with pulmonary vasculitis. She also has iron-deficient anaemia, hypertension and obstructive sleep apnoea (OSA). She is currently taking oral corticosteroids (which have been problematic with weight gain), immunosuppressives, antihypertensives and iron supplements. She is due for a review. Lung function results are as follows:
Previous results:
This visit Date 13/02/2012 16/07/2011 14/11/2010 FEV1 2.88 3.24 3.02 FVC 3.20 3.75 3.58 FEV1 /FVC 90 86 84 TLC 4.81 4.89 RV 1.70 1.39 FRC 1.92 2.11 RV/TLC 35 28 V A 4.2 4.7 4.5 TL CO 13.5 8.6 8.7 TL COHb corr 13.2 8.9 10.5 KCO 3.2 1.8 1.9 KCOHb corr 3.1 1.9 2.3
Cautionary statements :The test is of good quality. Technical interpretation :There appears to be a restrictive ventilatory defect on baseline spirometry; this is confirmed by a reduced TLC on static lung volumes. FRC is reduced in keeping with known obesity (BMI 56 kg/m2 ). Alveolar volume is reduced and carbon monoxide transfer factor, corrected for haemoglobin, is within normal limits (markedly elevated).Hb corr is elevated markedly. ?Current pulmonary haemorrhage. Possibly also a component of incomplete alveolar expansion. Clinical context :In comparison to previous results on 16/7/2011, there has been a significant fall in FVC and a significant increase in TL COHb corr . The possibility of current pulmonary haemorrhage should be considered in the light of the markedly elevated TL CO and KCO.
Final report : The test is of good quality. There is a restrictive ventilatory defect. FRC is reduced in keeping with known obesity (BMI 56 kg/m2 ). Alveolar volume is reduced, and carbon monoxide transfer factor, corrected for haemoglobin, is within normal limits, but higher than expected. KCO is markedly elevated. In comparison with previous results from 16/7/2011, there has been a significant fall in FVC and a significant increase in TL CO. In view of patient’s history of pulmonary haemorrhage, current pulmonary haemorrhage should be considered (TL CO and KCO z -scores > 1.96) as part of the clinical correlation.
Commentary : This case illustrates an example of when a finding in the normal range is actually abnormal. Most pathologies affecting gas exchange result in an abnormally low TL CO, hence, generally only a LLN for TL CO is set. In this case, the TL CO is markedly elevated (z -score > +3), KCO is above the upper limit of normal (ULN) (z -score > +6) and the alveolar volume is reduced (z -score < −2). These findings may represent incomplete alveolar expansion (e.g. chest wall restriction due to weight), microvascular dilation/congestion, increased pulmonary blood flow (e.g. post exercise, post pneumonectomy, obesity) or alveolar haemorrhage (1). Knowing the patient’s history, current pulmonary haemorrhage should be considered. Even though the usefulness of the KCO is somewhat controversial (Chapter 4), this case is an example, although relatively rare, of when it can be useful.
When comparing current results to previous results, we note that the difference in FEV1 measurements taken between 13/02/2012 and 16/07/2011 is 11% and 360 mL. This does not strictly satisfy the criteria for a significant change over time, but is a 360 mL fall in FEV1 of clinical significance in this case? Possibly, and it may be worth mentioning. Alternatively, as the change in FVC during the same period is considered to be clinically significant, the borderline fall in FEV1 may be of little consequence.
Case 2 Mrs Jenny Y, aged 74, presents for respiratory follow-up of her known asthma and bronchiectasis. Previous measurement of lung function has revealed a ‘restrictive’ pattern on spirometry.
Gender: Female Date: 21/4/2012 Age (yr): 74 Weight (kg): 60 Height (cm): 150.2 Race: Caucasian Clinical notes: Asthma/bronchiectasis. Restriction on spirometry Normal range Baseline z -scorePost-BD Change (%) Spirometry FEV1 (L) >1.20 1.06 −2.10 1.27 +20 FVC (L) >1.69 1.51 −2.14 1.67 +11 FEV1 /FVC (%) >65 70 −0.82 76 FEV1 /VC (%) >65 66 −1.55 58 Static lung volumes TLC (L) 3.45–5.20 4.10 −0.42 4.04 RV (L) <2.65 2.49 +1.22 1.86 FRC (L) 1.60–3.31 2.83 +0.72 2.23 RV/TLC (%) <54 60 +2.72 46 VC (L) >1.69 1.61 −1.86 2.18 +16 Single breath carbon monoxide transfer factor V I (L)1.52 V A (L)>3.1 2.5 −2.68 TL CO (mmol/min/kPa) >3.7 3.6 −1.65 TL CO Hb corr (mmol/min/kPa) 3.6 −1.73 KCO (mmol/min/kPa/L) 0.8–1.6 1.5 +1.18 KCOHb corr (mmol/min/kPa/L) 1.4 +1.01 Hb (g/dL) 14.1 Technical comment: Test performance was good. Note: Age > 70 years – reference values for SLV and gas transfer have been extrapolated.
Previous results:
Date 21/4/2012a 21/8/2011 17/11/2010 FEV1 – baseline 1.06 1.19 1.21 Post-BD 1.27 1.21 1.42 FVC – baseline 1.51 1.51 1.97 Post-BD 1.67 1.63 2.10 FEV1 /FVC – baseline 70 78 61 Post-BD 76 74 68 FEV1 /VC – baseline 66 Post-BD 58 65 V A 2.5 3.2 TL CO 3.6 5.5 TL COHb corr 3.6 5.6 KCO 1.5 1.7 KCOHb corr 1.4 1.7
Cautionary statements :The test is of good quality. Subject is >70 years and reference values for gas transfer and static lung volumes have been extrapolated and should be used with caution. Technical interpretation :There appears to be a restrictive ventilatory defect on baseline spirometry, however, baseline TLC is within normal limits and static lung volumes suggest gas trapping. There is a significant response to inhaled bronchodilator and post-BD FEV1 /VC<LLN, suggesting obstruction. Post-BD static lung volumes reveal resolution of gas trapping. Both alveolar volume and carbon monoxide transfer factor, corrected for haemoglobin, are reduced. As the KCO is in the normal range, the TL CO may be reduced due to the reduction in alveolar volume, parenchymal or pulmonary vascular disease or a combination of these. Clinical context :In comparison to previous results on 21/8/2011, there has been no significant change in spirometry. However, in comparison to results from 17/11/2010, there has been a significant fall in FVC and TL COHb corr . Results on this occasion suggest an obstructive ventilatory defect with a reversible component. Gas exchange impairment is evident, but the cause is unclear.
Final report : Reference values for gas transfer and static lung volumes have been extrapolated for age and should be used with caution. The test is of good quality. Although there appears to be a restrictive ventilatory defect on baseline spirometry, TLC is within normal limits and static lung volumes show evidence of gas trapping. The response to inhaled bronchodilator is significant and reveals an obstructive ventilatory defect. Gas trapping appears to be resolved on post-bronchodilator static lung volumes. Both alveolar volume and carbon monoxide transfer factor, corrected for haemoglobin, appear to be reduced. Results suggest that the TL CO may be reduced due to the reduction in alveolar volume, parenchymal or pulmonary vascular disease or a combination of these. In comparison to previous results on 21/8/2011, there has been no significant change in spirometry. However, in comparison to results from 17/11/2010, there has been a significant fall in FVC and TL COHb corr .
Results on this occasion suggest an obstructive ventilatory defect with a reversible component. Gas exchange impairment is evident, but the cause is unclear.
Commentary : This is a complex set of results with a number of competing issues. Firstly, the subject is 74 years old and the reference sets used in this book for gas transfer and static lung volumes are relevant for the age range 20–70 years. As we are extrapolating (or forecasting) how the reference values vary past this point, we need to add a cautionary statement to the report. Secondly, the baseline spirometry results suggest a restrictive ventilatory defect, while static lung volume measurements suggest an obstructive ventilatory defect. This highlights the limitations of using spirometry alone to diagnose restriction. Thirdly, the significant response in FEV1 and the decrease in RV/TLC with inhaled bronchodilator give clarity that the predominant abnormality is indeed airflow obstruction. Although not routinely performed in many laboratories, repeating the static lung volume measurements post-BD is, in this case, very useful. All of this needs to be reported in the context that the reference values being used for gas transfer and static lung volumes may not be correct.
Case 3 Ms Heidi R is a 71-year-old female with late-onset asthma. She has been noted to have a borderline low FVC on a previous spirometry test. She is referred for spirometry and static lung volume measurements.
Gender: Female Date: 12/2/2012 Age (yr): 71 Weight (kg): 69.5 Height (cm): 159 Race: Caucasian Clinical notes: Asthma. FVC borderline on last spirometry. ?TLC Normal range Baseline z -scorePost-BD Change (%) Spirometry FEV1 (L) >1.55 1.42 −2.02 1.50 +6 FVC (L) >2.13 2.12 −1.67 2.18 +3 FEV1 /FVC (%) >66 67 −1.47 69 FEV1 /VC (%) >66 53 −3.79 Static lung volumes TLC (L) 3.96–5.72 5.90 +1.97 RV (L) <2.76 3.23 +2.87 FRC (L) 1.90–3.62 3.51 +1.43 RV/TLC (%) <53 55 +2.04 VC (L) >2.13 2.67 Technical comment: Test performance was good.
Previous results:
Date 12/2/2012a 16/3/2011 FEV1 – baseline 1.42 1.37 Post-BD 1.52 1.60 FVC – baseline 2.12 2.17 Post-BD 2.18 2.12 FEV1 /FVC – baseline 67 63 Post-BD 69 75 FEV1 /VC – baseline 53 – Post-BD – –
Cautionary statements :The test is of good quality. Reference values for static lung volumes have been extrapolated for age (>70 years) and should be used with caution. Technical interpretation :There is an obstructive ventilatory defect (FEV1 /VC<LLN). Static lung volumes suggest possibly a large lung size with some evidence of gas trapping. The response to inhaled bronchodilator is not significant. Clinical context :Results suggest obstruction with no response to inhaled bronchodilator on this occasion. In comparison to previous results on 13/3/2011, there has been no significant change in spirometry.
Final report : Reference values for static lung volumes have been extrapolated for age and should be used with caution. The test is of good quality. There is an obstructive ventilatory defect with evidence of gas trapping. Static lung volumes also suggest large lung size. The response to inhaled bronchodilator is not significant. In comparison to previous results on 13/3/2011, there has been no significant change in spirometry.
Commentary : On examination of the forced spirometry results alone, there appears to be a borderline spirometry result – FVC and FEV1 /FVC at LLN. This makes interpretation difficult. The addition of static lung volumes reveals that FVC is likely to be reduced due to airflow limitation (TLC > LLN and RV/TLC > ULN) and confirms obstruction as FEV1 /VC (from static lung volumes) is reduced. TLC is elevated, but FRC is not – this suggests large lung size also.
In addition to these findings, the age of the subject and its impact on the reference values need to be considered. The reference sets used in this book for static lung volumes are relevant for the age range 20–70 years.
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