Stroke (STK) Initial Patient Population
The STK measure set is unique in that there are two distinct Initial Patient Populations (or sub-populations) within the measure set, each identified by a specific group of diagnosis codes, or lack thereof. The patients in each sub-population are counted in the Initial Patient Population of multiple measures. Hospitals utilizing STK for Joint Commission certification purposes will be required to use both the Ischemic and Hemorrhagic sub-populations. Hospitals utilizing STK for only CMS and/or Joint Commission accreditation purposes will use just the Ischemic sub-population.
The population of the STK measure set is identified using 4 data elements:
- ICD-10-CM Principal Diagnosis Code
- Admission Date
- Birthdate
- Discharge Date
The following is the STK Initial Patient Population’s measure breakdown:
Measures |
Initial Patient Population definition |
STK-2, 3, 4, 5, and 6 |
The count of all patients in sub-population 1 |
STK-1, 8, and 10 |
The count of all patients in sub-population 1 and 2 |
STK-1, 2, 3, 4, 5, 6, 8 and 10 are used for TJC Certification program and STK-4 is used for TJC Accreditation program.
Patients admitted to the hospital for inpatient acute care are included in one of the STK ICD sub-populations and are eligible to be sampled if they have:
1 –
Ischemic sub-population – Patients with an ICD-10-CM Principal Diagnosis Code for ischemic stroke as defined in Appendix A, Table 8.1, a Patient Age (Admission Date minus Birthdate) greater than or equal to 18 years and a Length of Stay (Discharge Date minus Admission Date) less than or equal to 120 days are included in the STK Initial Patient Population and are eligible to be sampled.
2 –
Hemorrhagic sub-population – Patients with an ICD-10-CM Principal Diagnosis Code for hemorrhagic stroke as defined in Appendix A, Table 8.2, a Patient Age (Admission Date minus Birthdate) greater than or equal to 18 years and a Length of Stay (Discharge Date minus Admission Date) less than or equal to 120 days are included in the STK Initial Patient Population and are eligible to be sampled.
NOTE: For CMS and Joint Commission accreditation purposes, hospitals will only be abstracting and submitting STK-4; therefore, only sub-population 1 (Ischemic patients) will be identified by the STK Initial Patient Population to be eligible for sampling.
NOTE: For Joint Commission certification purposes, hospitals will be abstracting and submitting data on all measures in the STK set; therefore, both sub-population 1 (Ischemic patients) and 2 (Hemorrhagic patients) will be identified by the STK Initial Patient Population to be eligible for sampling.
Stroke (STK) Initial Patient Population Algorithm Narrative
Variable Key: Patient Age, Initial Patient Population Reject Case Flag, and Length of Stay.
- Start STK Initial Patient Population logic sub-routine. Process all cases that have successfully reached the point in the Transmission Data Processing Flow: Clinical which calls this Initial Patient Population Algorithm. Do not process cases that have been rejected before this point in the Transmission Data Processing Flow: Clinical.
- Calculate Patient Age. Patient Age, in years, is equal to the Admission Date minus the Birthdate. Use the month and day portion of admission date and birthdate to yield the most accurate age.
- Check Patient Age:
- If the Patient Age is less than 18 years, the patient is not in the STK Initial Patient Population and is not eligible to be sampled for the STK measure set. Set the Initial Patient Population Reject Case Flag to equal Yes. Return to Transmission Data Processing Flow: Clinical in the Data Transmission section.
- If the Patient Age is greater than or equal to 18 years, continue processing and proceed to Length of Stay Calculation.
- Calculate the Length of Stay. Length of Stay, in days, is equal to the Discharge Date minus the Admission Date.
- Check Length of Stay:
- If the Length of Stay is greater than 120 days, the patient is not in the STK Initial Patient Population and is not eligible to be sampled for the STK measure set. Set the Initial Patient Population Reject Case Flag to equal Yes. Return to Transmission Data Processing Flow: Clinical in the Data Transmission section.
- If the Length of Stay is less than or equal to 120 days, continue processing and proceed to ICD-10-CM Principal Diagnosis Code Check.
- Check ICD-10-CM Principal Diagnosis Code
- If the ICD-10-CM Principal Diagnosis Code is on Table 8.1, the patient is in the first Ischemic Stroke sub-population and is eligible to be sampled for the first STK sub-population. Set the Initial Patient Population Reject Case Flag to equal No. Include the patient in the Initial Patient Population for the appropriate measures. Return to Transmission Data Processing Flow: Clinical in the Data Transmission section.
- For Joint Commission Only, if submitting data for STK Certification Program: If the ICD-10-CM Principal Diagnosis Code is on Table 8.2, the patient is in the second Hemorrhagic Stroke sub-population and is eligible to be sampled for the second STK sub-population. Set the Initial Patient Population Reject Case Flag to equal No. Include the patient in the Initial Patient Population for the appropriate measures. Return to Transmission Data Processing Flow: Clinical in the Data Transmission section.
STK Sample Size Requirements
Hospitals that choose to sample have the option of sampling quarterly or sampling monthly. A hospital may choose to use a larger sample size than is required.
Hospitals whose Initial Patient Population size is less than the minimum number of cases per quarter/month for the sub-population cannot sample that sub-population. Hospitals that have five or fewer discharges for the Ischemic STK sub-population (both Medicare and non-Medicare combined) in a quarter are not required to submit STK patient level data to the CMS Clinical Warehouse or the Joint Commission’s Data Warehouse if STK is being used for accreditation only purposes. Hospitals utilizing this measure set with the Joint Commission for certification purposes and have five or fewer discharges for the two combined STK sub-populations (both Medicare and non-Medicare combined) in a quarter are not required to submit STK patient level data to the Joint Commission’s Data Warehouse.
Regardless of the option used, hospital samples must be monitored to ensure that sampling procedures consistently produce statistically valid and useful data. Due to exclusions, hospitals selecting sample cases MUST submit AT LEAST the minimum required sample size.
The following sample size tables for each option automatically build in the number of cases needed to obtain the required sample sizes. For information concerning how to perform sampling, refer to the Population and Sampling Specifications section in this manual.
Quarterly Sampling
A modified sampling procedure is required for hospitals performing quarterly sampling for STK. The measure set contains two independent sub-populations: Ischemic STK patients and Hemorrhagic STK patients. The two sub-populations must be sampled independently from each other.
CMS Clinical Warehouse and the Joint Commission’s Data Warehouse for accreditation only purposes: To determine if a hospital may choose to not submit STK patient level data, the count of the Ischemic sub-population discharges, for the quarter, must be five or less.
Joint Commission certification purposes: To determine if a hospital may choose to not submit STK patient level data, the count of the discharges, for the quarter, for the two sub-populations must be five or less (i.e., the combined count of discharges equals the count of all patients in the Ischemic Patient Sub-population [1] plus the count of all patients in the Hemorrhagic Patient Sub-population [2].
1.Hospitals selecting sample cases for the Ischemic sub-population must ensure that its Initial Patient Population and sample size for the Ischemic sub-population meets the following conditions:
Quarterly Sample Size
Based on Initial Patient Population Size
for Ischemic Patient Sub-Population
Hospital’s Measure
Average Quarterly Initial Patient Population N |
Minimum Required Sample Size n |
≥ 900 |
180 |
226-899 |
20% of the Initial Patient Population |
45-225 |
45 |
6 - 44 |
No sampling; 100% of the Initial Patient Population is required |
0 - 5 |
Submission of patient level data is not required; if submission occurs, 100% Initial Patient Population required. |
2.Hospitals submitting STK data for Joint Commission certification purposes will select sample cases for the Hemorrhagic sub-population, ensuring that its Initial Patient Population and sample size for the Hemorrhagic sub-population meets the following conditions:
Quarterly Sample Size
Based on Initial Patient Population Size
for Hemorrhagic Patient Sub-Population
Hospital’s Measure
Average Quarterly Initial Patient Population N |
Minimum Required Sample Size n |
≥ 900 |
180 |
226-899 |
20% of the Initial Patient Population |
45-225 |
45 |
6 - 44 |
No sampling; 100% of the Initial Patient Population is required |
0 - 5 |
Submission of patient level data is not required; if submission occurs, 100% Initial Patient Population required. |
Monthly Sampling
A modified sampling procedure is required for hospitals performing monthly sampling for STK. The measure set contains two independent sub-populations: Ischemic STK patients and Hemorrhagic STK patients. The two sub-populations must be sampled independently from each other.
1. Hospitals selecting sample cases for the Ischemic sub-population must ensure that its Initial Patient Population and sample size for the Ischemic sub-population meets the following conditions:
Monthly Sample Size
Based on Initial Patient Population Size
for Ischemic Patient Sub-Population
Hospital’s Measure
Average Monthly Initial Patient Population N |
Minimum Required Sample Size n |
≥ 300 |
60 |
76-299 |
20% of the Initial Patient Population |
15-75 |
15 |
< 15 |
No sampling; 100% Initial Patient Population required |
2. Hospitals submitting STK data for Joint Commission certification purposes will select sample cases for the Hemorrhagic sub-population, ensuring that its Initial Patient Population and sample size for the Hemorrhagic sub-population meets the following conditions:
Monthly Sample Size
Based on Initial Patient Population Size
for Hemorrhagic Patient Sub-Population
Hospital’s Measure
Average Monthly Initial Patient Population N |
Minimum Required Sample Size n |
≥ 300 |
60 |
76-299 |
20% of the Initial Patient Population |
15-75 |
15 |
< 15 |
No sampling; 100% Initial Patient Population required |
Sample Size Examples
Note: Hospitals utilizing STK for Joint Commission certification purposes must include all sampled STK sub-populations in the calculation of all STK measures. All of the STK measures’ specific exclusion criteria are used to filter out cases that do not belong in the measure denominator. Hospitals utilizing STK for CMS purposes or Joint Commission accreditation only purposes will use the Ischemic sub-population [1] in the calculation of STK-4.
Quarterly sampling
- Quarterly sampling for the Ischemic sub-population:
- A hospital’s Ischemic sub-population is 392 during the first quarter. Using the quarterly sampling table for the Ischemic sub-population, the sample size required is 20% of this sub-population, or 79 cases for the quarter (twenty percent of 392 equals 78.4 rounded up to the next whole number equals 79)
- A hospital’s Ischemic sub-population is 100 during the first quarter. The required quarterly sample is 45 cases.
- For CMS purposes and Joint Commission accreditation only purposes: A hospital’s Ischemic sub-population is 4 patients during the first quarter. Since the Initial Patient Population for STK is 4, the hospital may choose to not submit patient level data.
- If the hospital chooses to submit patient level data:
- CMS: the quarterly sample size would be 1-4 of the total STK cases.
- Joint Commission accreditation only: the required quarterly sample size would be 100% of the patient population or 4 cases for the quarter.
- For Joint Commission certification purposes: A hospital’s Ischemic sub-population is 5 patients during the first quarter. Using the quarterly sampling table for the Ischemic sub-population, the sample size is less than the minimum required quarterly sample size, so 100% of this sub-population is sampled.
- Quarterly sampling for the Hemorrhagic sub-population for Joint Commission certification purposes:
- A hospital’s Hemorrhagic sub-population is 392 during the first quarter. Using the quarterly sampling table for the Hemorrhagic sub-population, the sample size required is 20% of this sub-population, or 79 cases for the quarter (twenty percent of 392 equals 78.4 rounded up to the next whole number equals 79).
- A hospital’s Hemorrhagic sub-population is 3 patients during the first quarter. Using the quarterly sampling table for the Hemorrhagic sub-population, the sample size is less than the minimum required quarterly sample size, so 100% of this sub-population is sampled.
- A hospital’s Hemorrhagic sub-population is 100 during the first quarter. The required quarterly sample is 45 cases.
- Quarterly sampling for the two combined populations for Joint Commission certification purposes.
- The STK Initial Patient Population sizes for a hospital are 392 and 5 patients respectively per the sub-populations for the quarter. Since the total Initial Patient Population for STK is 397, the hospital must submit patient level data. The required quarterly sample sizes for each sub-population would be 79 and 5.
- The Ischemic sub-population has 392 patients per quarter, which requires a 20% sample size, or 79 cases (twenty percent of 392 equals 78.4 rounded to the next highest whole number equals 79).
- The Hemorrhagic sub-population is less than the minimum required quarterly sample size, so 100% of this sub-population is sampled.
- The STK Initial Patient Population sizes for a hospital are 1 and 3 patients respectively per the sub-populations for the quarter. Since the total Initial Patient Population for STK is 4, the hospital may choose to not submit patient level data. If the hospital chooses to submit patient level data:
- The Joint Commission: the required quarterly sample size would be 100% of the patient population or 4 cases for the quarter.
Monthly Sampling
- Monthly sampling for the Ischemic sub-population:
- A hospital’s Ischemic sub-population is 228 during March. Using the monthly sampling table for the Ischemic sub-population, the sample size required is 20% of this sub-population, or 46 cases for the quarter (twenty percent of 228 equals 45.6 rounded up to the next whole number equals 46).
- A hospital’s Ischemic sub-population is 316 during January. The required quarterly sample is 60 cases.
- A hospital’s Ischemic sub-population is 5 patients during February. Using the monthly sampling table for the Ischemic sub-population, the sample size is less than the minimum required monthly sample size, so 100% of this sub-population is sampled.
- Monthly sampling for the Hemorrhagic sub-population for Joint Commission certification purposes:
- A hospital’s Hemorrhagic sub-population is 228 during March. Using the monthly sampling table for the Hemorrhagic sub-population, the sample size required is 20% of this sub-population, or 46 cases for the quarter (twenty percent of 228 equals 45.6 rounded up to the next whole number equals 46).
- A hospital’s Hemorrhagic sub-population is 3 patients during January. Using the monthly sampling table for the Hemorrhagic sub-population, the sample size is less than the minimum required quarterly sample size, so 100% of this sub-population is sampled.
- A hospital’s Hemorrhagic sub-population is 316 during February. The required monthly sample is 60 cases.