Breast cancer – standardised 30-day in-hospital mortality ratio following surgery

Metric

The ratio of the observed number of deaths to the expected number of deaths, multiplied by 100.

Numerator

All spells with method of discharge as death (DISMETH=4 or 5), within 30 days of the procedure date.

Denominator

Expected number of in-hospital deaths for patients having a breast excision procedure with breast cancer as a primary diagnosis.
Any inpatient with a primary procedure of one of the following OPCS codes:

• B27 Total excision of breast
• B28 Other excision of breast

Equivalent to combining “Excision of breast” and “Excision of breast lump” procedure groups in the DFI tools

And a primary diagnosis of one of the following ICD10 codes:

• C50 Malignant neoplasm of breast

Data Source

SUS – CDS

Time frame

April 2010 – March 2011

Basis

Acute trust

Statistical methods used

Expected counts are derived from logistic regression, adjusting for:

• Sex
• Age on admission (in five year bands up to 90+)
• Admission method (non-elective or elective)
• Socio-economic deprivation quintile of the area of residence of the patient (based on the Carstairs Index)
• Procedure subgroup
• Co-morbidities (Dr Foster methodology)
• Number of previous emergency admissions in last 12 months
• Year of discharge (financial year)
• Palliative care (if any episode in the spell has the treatment function code 315 or contains ICD10 code Z515 in any of the diagnoses fields)
• Month of admission
• Source of admission

Logistic regression

The ratio is calculated by dividing the actual number of readmissions by the expected number and multiplying the figure by 100. It is expressed as a relative risk, where a risk rating of 100 represents the national average. If the trust has a SRR of 100, that means that the number of patients who were readmitted is exactly as would be expected taking into account the standardisation factors. A SRR above 100 means more patients were readmitted than would be expected; one below 100 means that fewer than expected were readmitted.

Control limits

Control limits tell us the range of values which are consistent with random or chance variation. Data points falling within the control limits are consistent with random or chance variation and are said to display ‘common-cause variation’; for data points falling outside the control limits, chance is an unlikely explanation and hence they are said to display ‘special-cause variation’ – that is, where the trust’s rate diverges significantly from the national rate.

Data points falling above the upper 99.8% control limit are said to be significantly ‘higher than expected’, data points falling below the lower 99.8% control limit are said to be significantly ‘lower than expected’, otherwise ‘within expected range’.

Notes

ICD10 contains no TNM staging information therefore we have tried to reproduce the essence using primary and secondary diagnosis fields. ‘Local spread’ requires the presence of a code for a local lymph node AND the absence of codes for distant nodes or organs. ‘Distant spread’ requires the presence of a code for distant nodes or organs (there may also be codes for local node or organ involvement present).

The denominator procedure groups “Excision of breast” and “Excision of breast lump” will both be organised to contain the following procedure subgroups within the DFI tools and for the purposes of risk adjustment. This indicator is a collation of the first 3 subgroups.

Subgroup title	Primary diagnosis codes	Secondary diagnosis codes
1. Breast only, no nodes	C50	No other C
2. Breast only, local nodes	C50	C773 (axillary and upper limb lymph nodes) and no other C77-C79
3. Breast only, distant spread	C50	C77-C79 excl C773
4. All other diseases	Not C50	Any

Comment from the Dr Foster Hospital Guide Team

We suggest further refining the table above to provide greater definition. The new codes would be:

Subgroup title	Primary diagnosis codes	Secondary diagnosis codes
1. Breast, no nodes	C50	Any excl C77-C79
2. Breast, local spread	C50	C773 (axillary and upper limb lymph nodes) if no other C77-C79
3. Breast, distant spread	C50	Any C excl C773
4. All other diseases (includes ca in situ in breast)	Any except C50	Any