FREE
The free Clinical Research Planner — protocol snapshot with space for visit windows, daily clinical flow, PI signature tracking, and monitor-readiness checklists.
Download the free planner →Clinical research coordinators work at the intersection of medicine, science, and documentation, and that intersection is full of unit mismatches. A protocol written by a European sponsor may express weight in kilograms and lab values in SI units (mmol/L, µmol/L), while your institution's lab reports results in conventional US units (mg/dL, mEq/L). Eligibility criteria, dose calculations, and safety assessments all depend on using the right units, and a conversion error can mean a missed eligibility finding, an incorrect dose, or a misinterpreted lab value.
The most dangerous unit errors are the ones that look plausible. A serum creatinine of 1.2 mg/dL is normal. A serum creatinine of 1.2 µmol/L would be an impossibly low value (typical range is 50–110 µmol/L). If a number looks wrong for the patient in front of you, check your units before proceeding — it may simply be a unit mismatch between the protocol and the lab report. When transcribing values into CRFs or eligibility worksheets, always note the unit alongside the value. A lab result recorded as "1.0" without a unit is an incomplete entry.
The International System of Units (SI) is the standard in most of the world and in international regulatory submissions. The United States commonly uses conventional (non-SI) units for many clinical measurements. When working with multinational trials or sponsor-originated documents, always confirm which unit system the protocol is using. When in doubt, include both values with their respective units in your source documentation — it adds seconds of work and can prevent hours of query resolution later.
Unit conversion errors are a category of clinical trial error that disproportionately generates protocol deviations relative to the effort required to prevent them. The math involved is simple. The consequences — enrolling an ineligible participant, administering the wrong dose, misinterpreting a safety value — are not. Understanding the specific conversions that most frequently cause problems in clinical research, and the documentation standard that prevents them from becoming deviations, is more practical than knowing the conversion factors by heart.
Serum creatinine is the most clinically significant unit mismatch in clinical research. US laboratories report creatinine in milligrams per deciliter (mg/dL). European and international laboratories, and many academic centers, report in micromoles per liter (µmol/L). The conversion factor is 88.4: 1 mg/dL = 88.4 µmol/L.
The dangerous scenario: a participant's eligibility creatinine comes back as 106 µmol/L. The protocol requires creatinine ≤ 1.5 mg/dL. Without converting, 106 looks like it might be close to 106 mg/dL, which would be catastrophically elevated. But 106 µmol/L is actually 1.2 mg/dL, well within normal range and well within the eligibility criterion. The inverse error — treating 1.2 mg/dL as if it were 1.2 µmol/L (which would be impossibly low) — would cause an unnecessary screen failure.
Both error directions exist. The solution is to verify the unit on every creatinine result before entering it into an eligibility calculation, and to document the unit alongside the value in your eligibility worksheet and source documentation. "Creatinine 1.2 mg/dL" is a complete entry. "Creatinine 1.2" is not.
Most investigational product doses in oncology and many other therapeutic areas are weight-based: a fixed number of milligrams or micrograms per kilogram. US participants are typically weighed in pounds at clinical sites; protocols specify doses in mg/kg. The conversion is 1 kg = 2.20462 lbs, or equivalently, lbs ÷ 2.205 = kg.
The error pattern here is simple but serious: using the weight in pounds directly in a mg/kg dose calculation. A participant weighing 165 lbs is 74.8 kg. A dose of 2 mg/kg should be 149.7 mg. If the pounds value of 165 is used instead, the calculated dose would be 330 mg, more than double the correct dose. This error is less common than it once was because most electronic scales and EDC systems prompt for weight unit, but it still occurs when weight is recorded in source and transcribed manually into a dose calculation worksheet.
Temperature conversions appear in two distinct clinical trial contexts: adverse event assessment and drug storage. The conversion is °F = (°C × 9/5) + 32, or equivalently °C = (°F − 32) × 5/9.
For adverse event assessment, many oncology protocols define fever as an adverse event threshold in Celsius: "Grade 1 fever: 38.0°C–39.0°C." Your participant's temperature was documented in Fahrenheit: 101.5°F. Converting: (101.5 − 32) × 5/9 = 38.6°C — a Grade 1 fever that must be recorded as an adverse event. Without converting, the documentation may simply record "101.5°F" with no AE entry, leaving the clinical interpretation to whoever next reviews the chart, and creating a source documentation inconsistency if the protocol's AE definitions are in Celsius.
For drug storage, protocols typically specify temperature ranges in Celsius: "Store at 2°C–8°C (36°F–46°F)." If your site's refrigerator temperature log records in Fahrenheit, verify that the acceptable range has been correctly converted and posted. A storage temperature of 40°F is within range (4.4°C). A storage temperature of 40°C (104°F) is a critical excursion. When reviewing temperature logs, always confirm which unit is being recorded.
Blood glucose is reported in mg/dL in the United States and in mmol/L internationally. The conversion is 1 mmol/L = 18.0 mg/dL. This conversion matters in trials involving metabolic endpoints, diabetes populations, or drugs with glucose-related safety profiles. A fasting glucose of 7.0 mmol/L is 126 mg/dL — meeting the ADA threshold for diabetes. Misreading 7.0 as 7.0 mg/dL (a physically implausible value for blood glucose) would cause obvious confusion; misreading 126 mg/dL as 126 mmol/L (equivalent to 2,268 mg/dL — incompatible with life) would also generate an alert. The unit mismatch that actually causes problems is subtler: using an unconverted value in an eligibility calculation or AE grading table that uses the opposite unit system.
Under ALCOA+ principles, as described in FDA's data integrity guidance — Attributable, Legible, Contemporaneous, Original, Accurate, plus Complete, Consistent, Enduring, and Available, all data entered into source documents must be complete and accurate. A lab value without its unit is not complete. A converted value without documentation of the original value and conversion method is not attributable.
The practical standard: when you convert a value for use in an eligibility calculation or CRF entry, document the original value with its unit, the converted value with its unit, and the conversion used. "Creatinine: 106 µmol/L (= 1.2 mg/dL per conversion factor 88.4)" is an adequate source documentation entry. It is traceable, verifiable, and leaves no ambiguity for a monitor reviewing the eligibility worksheet months later.