CKiD Summary Files & Codebooks

Below are the codebooks for and descriptions of the main summary files used in the CKiD Study. We have also provided a combined version of all the codebooks, a folder of all the individual codebooks, as well as a document with all the CKiD study forms, which can all be found below.


VERT_DATEBASE is an ID-visit file. It provides visit numbers, corresponding study dates and status of visit. The status of each visit (file record) is defined as regular (occurring per study protocol), irregular (occurring on an accelerated schedule due to an anticipated transition to renal replacement therapy), disenrollment due to participant withdrawal, initiation of RRT, or death (documented via the disenrollment form), or phone-follow-up or in-person interview (non-clinical visit). This file also includes date of first transplant or dialysis (if this has occurred). 


KIDHIST is a horizontally structured data file with one record for each participant. It contains key clinical and date variables describing each participant’s kidney disease history. Clinical variables include primary CKD diagnosis, current CKD status (no history of RRT, on dialysis, transplant recipient, and in rare cases, death), study status at last visit, and parametric estimates of each participant’s baseline GFR and percentage change in GFR over follow-up. Date variables document the following occurrences: birth, date of kidney disease onset, study baseline, last date RRT free, first transplant, first dialysis, last date known alive (i.e., last contact date), and in rare cases, date of death. This file also includes participant sex. 


SOCDEM is an ID-visit file, containing sociodemographic variables such as race, ethnicity, household income, maternal education, family size, and marital status of birth parents. Please note that household income, maternal education, family size and marital status are not fixed at baseline; they can change throughout the course of study participation. 


GFRCALIBRATEDSUMMARY is an ID-visit file. It provides a complete description of all variables related to both the measurement and estimation of a participant’s glomerular filtration rates (GFR). This includes all variables related to the iohexol-infusion protocol (iGFR) as well as the biomarkers (serum creatinine, BUN and Cystatin C) that are used to estimate GFR. Estimated GFR (eGFR) variables includes both eGFR2012 eGFR (defined as 41.3*[ht/serum creatinine]) based on equations from Schwartz et al. 2012 in Kidney International, and CKiD Under 25 (U25) eGFR based on equations from Pierce et al. 2021 in Kidney International.


OUTCOMES is an ID file, with one entry per participant. This file includes information on important study outcomes, such as dialysis, transplant, or death (in rare cases). It also includes information on the initiation of PIP visits (visits for continued follow-up completed by phone, in-person or by mail), ePIP visits (PiPs completed electronically), or date of disenrollment. 


LABMARKERS is an ID-visit file containing variables for laboratory markers. The file includes basic metabolic panel, complete blood count (CBC), urine analysis, intact parathyroid, c-reactive protein, lipid panel and iron results, as well as calculated proteinuria, acidosis, hypoalbuminemia, abnormal calcium and phosphate (based on KDOQI thresholds), calcium-phosphate product, elevated CRP, anemia and hemoglobin z-scores and percentiles based on age, sex and race per CDC guidelines. 


CARDIO is an ID-visit file containing variables summarizing blood pressure variables from the clinic and ambulatory blood pressure monitoring (ABPM) protocol. Summary clinic BP measurements include SBP and DBP index (based on age, sex and height), and z-scores and percentiles adjusted to age, sex and height. Blood pressure staging, based on 2017 American Academy of Pediatrics guidelines, are also included. Summary ABPM variables include mean systolic and diastolic BP over 24 hour monitoring, load (i.e. % of readings that are over the 95% Soergel limit), dipping status and success rates.


NEUROSUMMARY is an ID-visit file containing key variables from the Neurocognitive battery, the Behavioral battery as well as Quality of Life (QoL) measurements. Key variables include: 1) Verbal IQ, Performance IQ and Full Scale IQ as measured by the Mullen, WPPSI-III or WASI; 2) scaled overall achievement score as measured by the WIAT-II-A; 3) scaled attention scores as measured by the K-CPT or CPT-II; 4) scaled executive functioning summary scores as measured by the BRIEF-P or BRIEF and 5) parent and child QoL sub-scale and overall scores as measured by the PedsQL inventory. Additional variables are added as the need arises. 


GROWTH is an ID-visit file, which contains key variables describing markers of growth, such as height, weight, body mass index (BMI), body surface area (BSA), and Tanner staging, as well as variables on birth history, such as low birth weight (<2500 grams), premature birth (gestational age <36 weeks), small for gestational age (birth weight <10th percentile for gestational age), and intensive care unit immediately after delivery. Age and sex adjusted percentiles and z-scores are calculated based on CDC growth charts with normative data. 


MEDSUM_FULL contains one record per medication per participant-visit, and provides more detailed information for each medication, including dosing amounts and schedules, as well as a set of variables that describe the participant’s adherence to the medication. 


MEDSUM_SHORT data file is structured as one record per participant-visit, and summarizes whether or not (yes/no) the study participant has been prescribed any medication during the past 30 days that falls into one of several major medication or supplement classes, such as antihypertensives, ESA’s, growth hormones, immunosuppressives, anticholinergics, and antidepressants (to name a few). 


ECHO is an ID-visit dataset of summarized echocardiogram scans, collected at biennial visits. The following variables are included in this dataset: left ventricular mass (LVM, including LVM z-score adjusted for lean body mass), left ventricular geometry, left ventricular hypertrophy, ascending aortic distensibility, ascending aortic stiffness, and shortening fraction abnormalities. 


GRIPSTRENGTH is an ID-visit data file. It includes data on grip strength tests, including grip strength (in kilograms and pounds), and maximum grip strength (for left and right hand in pounds). 


NUTRIENTS is an ID-visit data file. It includes data on participant nutrient intake, such as total energy intake, total fat, carbohydrates, proteins, sodium, potassium, calcium, omega-3 fatty acids, dietary fiber, vitamins, and caffeine, among others. These data were generated from FFQs (food frequency questionnaires).  


CIMT is an ID-visit file with data on Carotid Intima-Media Thickness (cIMT) tests. It also includes data on  carotid artery distensibility, stiffness, and pressure strain modulus. 


CENSUS is an ID-visit file. It includes census data for the corresponding participant from CBG (Census Block Group), such as FIPS code, total population, average household size, owner vs. renter occupied housing units, median and average household income.