What is the first-line investigation for acute interstitial nephritis?

The first-line investigation for acute interstitial nephritis is indeed a full blood count along with urea and electrolytes. This testing is essential as it provides fundamental insights into kidney function, including assessing renal impairment and evaluating electrolyte balance.

Specifically, a full blood count can help identify any underlying systemic conditions, such as infection or inflammation, which may contribute to acute interstitial nephritis. Monitoring urea and electrolytes is critical in understanding the degree of renal dysfunction, which can guide further management.

In acute interstitial nephritis, the condition often manifests as an increase in serum creatinine and disturbances in electrolyte levels. Initial laboratory tests like urea and electrolytes allow for a quick assessment of kidney function and help rule out other causes of acute kidney injury.

Other options like urine culture might be useful for ruling out infections, but they are not the first step in diagnosing acute interstitial nephritis. Similarly, a CT scan might be considered in cases of suspected obstruction but is not specific for acute interstitial nephritis. A renal biopsy, while definitive for diagnosis, is usually reserved for cases where the diagnosis remains uncertain after non-invasive tests are performed. Therefore, the combination of a full blood count and urea/electrolytes is