Urine Test Strips as a Bedside Diagnostic Aid to Rule out Blood in CSF: A Validation

Patients presenting to the emergency department with acute-onset, atypical headaches require an evaluation for subarachnoid hemorrhage (SAH). The standard evaluation for SAH includes noncontrast computed tomography of the head and, if negative, a lumbar puncture to determine the presence of blood in the cerebrospinal fluid (CSF). In austere environments without full laboratory capabilities, a rapid bedside diagnostic test allowing clinicians to rule out SAH would reduce costly transfers of patients requiring further evaluation. CSF samples obtained while evaluating patients for potential SAH were tested with the blood panel of Bayer Multistix urine test strips.

We compared the test strip color change to the number of red blood cells per high power field found on laboratory analysis of the CSF.

The sensitivity of the Multistix for detecting red blood cells in the CSF was 100%, with a specificity of 56%. The positive predictive value was 37%, and the negative predictive value was 100%.

These results are encouraging and may form the basis for potential use of urine test strips as a tool to rule out subarachnoid blood in austere environments, but the test strips' low specificity limits their usefulness as a practical clinical tool at this time.